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Clinical and Epidemiological Aspects of Clostridium difficile
Clinical Microbiology Newsletter Vol. 30, No. 12
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June 15, 2008
Clinical and Epidemiological Aspects of Clostridium difficile Matthew T. Oughton, MD, FRCPC1 and Mark A. Miller, MD, FRCPC,1,2,3 1Faculty of Medicine, McGill University, 2 Division of Clinical Microbiology and 3Division of Infectious Diseases, Department of Medicine, SMBD-Jewish General Hospital, Montreal, Quebec, Canada
Abstract Clostridium difficile-associated disease (CDAD) has increased in frequency and severity throughout North America and Europe over the last 5 years, largely due to the emergence of the NAP1 epidemic strain. This transformation of a formerly mild disease into one that can cause severe morbidity and mortality within a few days has challenged our entire approach to this serious infection. Institutions require accurate and rapid diagnostics for early detection of cases and possible outbreaks in order to initiate specific therapy and implement effective infection control. The optimal hand hygiene techniques, barrier methods and environmental cleaning practices that would diminish transmission remain uncertain. Clinicians need reliable research that can pinpoint the most important factors determining severity of disease and relapse. Epidemiologic and molecular analyses are vital in order to understand the local and international transmission of this disease, as well as its recent change in pathogenicity. As well, further examination of this infection is crucial in order to find effective prophylactic maneuvers and optimal therapies. This review discusses the changing epidemiology of CDAD across North America and internationally, as well as the common diagnostic methods and molecular typing tools for this pathogen. Finally, the current evidence supporting conventional, novel, and non-antimicrobial preventative and therapeutic options is examined.
Introduction A new era for Clostridium difficile began early this millennium, causing problems for patients and challenges for health care workers that continue to the present day. Symptomatic disease caused by C. difficile has been called “C. difficile-associated diarrhea,” “C. difficile-associated disease” (both abbreviated as “CDAD”), or “C. difficile infection.” What had been considered largely a “nuisance disease,” causing mild diarrhea and responding to withdrawal of the inciting antibiotic or a short course of metronidazole, turned quickly into epidemics that closed down hospital wards, left
Mailing Address: Mark A. Miller, M.D., FRCPC, SMBD-Jewish General Hospital, 3755 Cote-Ste-Catherine Road, Suite G-139, Montreal, Quebec, Canada H3T 1E2. Tel: 514-340-8294. Fax: 514-340-7546. E-mail: [email protected]
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patients in intensive care facing total colectomies, and dramatically illustrated the importance of basic infection control precautions. This rapidly evolving epidemiology gave new importance to some lingering clinical questions: “What factors have driven this sudden change in disease frequency and severity?” Which patients would benefit from surgical intervention?” “What is the optimal therapy?” “How should recurrent disease be managed?” This paper will review the data that has begun to provide some answers to these questions.
Epidemiology
rise in regional and national epidemiologic studies from countries across North America, Europe, and southeastern Asia. These outbreaks have been largely, although not exclusively, driven by the newly recognized North American pulsed-field type 1 (NAP1) strain, alternately known as ribotype 027, restriction endonuclease type BI, toxinotype III, or the “hypervirulent strain” (depending on the typing methodology and nomenclature used), which carries (i) genetic mutations in the tcdC toxin regulator gene, (ii) binary toxin genes, and (iii) fluoroquinolone resistance mutations.
Prior to 2001, comprehensive epidemiologic studies of C. difficile and CDAD were limited, as might be expected for a disease lacking mandatory reporting due to its low severity and inexpensive treatment. The current era of increased CDAD frequency and severity has prompted a concomitant © 2008 Elsevier
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United States CDAD incidence across America has been increasing, as seen in analyses of two large national medical databases. In hospitals participating in the National Nosocomial Infections Surveillance System from 1987 to 2001 (1), CDAD incidence gradually increased in the intensive care units (ICUs) of large (>500-bed) hospitals. With ICU data excluded, incidence rates increased only in smaller (<250-bed) hospitals, particularly on medical wards; the cause of this apparent discrepancy remains unclear. A recent cohort analysis of patients from the Nationwide Inpatient Sample, representing 1,000 hospitals across 35 states, found a doubling of the C. difficile colitis incidence rate from 261 cases per 100,000 discharged patients in 1993 to 546 cases per 100,000 discharged patients in 2003 (2); half of that increase occurred in the final 2 years of the study. Most recently, population-based estimates of C. difficile mortality rates rose more than fourfold, from 5.7 per million population in 1999 to 23.7 per million population in 2004 (3). The presence of the NAP1 strain had been identified in at least 27 states as of April 2007 (4) and has been reported as the main cause of out-breaks in several states (5,6). The impacts of CDAD on individuals and healthcare institutions in America are considerable. One prospective follow-up of 271 patients at a teaching hospital in Boston determined that hospital-acquired CDAD resulted in a median 54% increase in hospital costs (an additional $3,669) and a median 3.6-day-longer hospital admission compared to patients without CDAD (7). It should be noted that this study used data from patients with predominantly mild to moderate CDAD admitted from January to May 1998; thus, it likely
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underestimates costs and lengths of stay due to the more severe disease caused by NAP1 and related strains. A recent summary of case reports across four states identified severe CDAD in community-dwelling patients and peripartum women, groups usually considered as low risk for CDAD (8); however, the C. difficile strains in these cases were not typed, and therefore, the cases were not necessarily due to the NAP1 strain.
Canada The baseline for CDAD frequency, severity, and cost to the healthcare system in Canada was established in the Canadian Nosocomial Infection Surveillance Program (CNISP) survey of 2,062 patients from 19 institutions in eight provinces during 1997 (9). Thirteen percent of all inpatients tested for diarrhea met the case definition for CDAD, yielding an incidence of 5.9 cases per 1,000 patient admissions. Complications occurred in 8% of these patients, with 1.5% of all mortality being attributed directly or indirectly to CDAD. Increases in CDAD frequency and mortality were first widely reported in mid-2004 (10), although recent studies have retrospectively identified increases from as early as December 2002 (11). A study of 12 Quebec hospitals during the first half of 2004 (12) determined the incidence to be 22.5 per 1,000 patient admissions, with an attributable mortality rate of 6.9%; both rates represented approximately fourfold increases compared to historic rates determined by the CNISP study. The mortality burden varied directly with patient age, increasing from 1.2% in patients aged 41 to 50 to 10% in patients aged 81 to 90 and 14% in patients older than 90. Although the NAP1 strain predominated in this study, case severity was significantly associated not with strain type, but rather with the presence
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of two putative virulence factors: binary toxin and a partial deletion in the negative toxin regulator gene tcdC. A later prospective study involving 88 Quebec hospitals found that severe disease was twice as frequent in patients infected by strains possessing these two virulence factors (13). A fivefold increase in CDAD incidence was described in a population-based retrospective study from one teaching hospital in Quebec over the 12-year period from 1991 to 2003 (14). This study found a concomitant doubling in the proportion of CDAD complications (death, toxic megacolon, intestinal perforation, colectomy, or shock requiring vasopressors); the increases in incidence and complication rates largely occurred in the last year of the study. The same group subsequently reported that the risk of recurrent CDAD at 60 days more than doubled, from 21% during 1991 to 2002 to over 47% in 2003 to 2004 (15). These findings demonstrated that CDAD in Quebec had suddenly and dramatically increased in severity, supporting the argument that emergence of a highly virulent strain or strains was largely responsible. Another survey across three Canadian provinces documented the absence of C. difficile ribotype 027 in Quebec isolates during 2000 to 2001, followed by its abrupt rise 3 years later (16). A follow-up CNISP survey of 34 hospitals across nine provinces during November 2004 to April 2005 revealed an unchanged overall mean CDAD incidence at 6.4 per 10,000 patient days (17). However, the incidence in Quebec, at 11.9 per 10,000 patient days, remained almost double the historic rate.
Europe and Asia The recent European experience with CDAD has largely followed the patterns seen in North America. One
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recent review stated that C. difficile was responsible for twice as many deaths as methicillin-resistant Staphylococcus aureus in the United Kingdom during 2003 (18). The same article claimed the attributable mortality rate had increased 2.3-fold from 1999 to 2004. The NAP1 strain has been recognized as the cause of outbreaks across six European countries (United Kingdom, Netherlands, Belgium, France, Austria, and Ireland) and has been detected sporadically in at least six more (Switzerland, Luxembourg, Poland, Denmark, Sweden, and Finland) (19,20). The exact origin of the NAP1 strain is uncertain, although historic examples of the strain appear in at least two large European collections. It was identified in a Swedish strain collection of isolates dating from as early as 1997 (19), and it is stored as isolate CD 196 (21) in a reference bank of the Institut Pasteur, originally isolated in France during 1984 (22) and the isolate in which binary toxin was first reported (23). The prevalence of the NAP1 strain varies widely by country; a survey of 149 randomly selected isolates collected throughout southeast Scotland from August to October 2005 found no ribotype 027 isolates (24). A frequent trend toward high frequency of fluoroquinolone resistance in C. difficile isolates has appeared in reports from the United Kingdom (25), The Netherlands (26), Spain (27), and Poland (28). There is less epidemiologic information on C. difficile and CDAD in Asian countries. One survey of isolates collected in Japan, Korea, and Indonesia found a wide variety of toxinotypes, with toxinotype 0 predominating (29). An analysis of 148 isolates from one Japanese teaching hospital identified an epidemic strain (PCR ribotype smz) responsible for outbreaks in multiple hospitals, along with a single isolate of NAP1 collected in 2001 that was fluoroquinolone susceptible and associated with community onset disease (30). The NAP1 isolate was again detected in Japan from a patient hospitalized in March 2005 (31). The authors noted that the isolate was also susceptible to fluoroquinolones, which may have explained its absence from outbreaks in Japanese healthcare facilities. Clinical Microbiology Newsletter 30:12,2008
Molecular Epidemiology As illustrated by the long list of names sometimes assigned to the virulent strain responsible for numerous outbreaks (ribotype 027/toxinotype III/pulsed-field gel electrophoresis [PFGE] pattern NAP1/restriction endonuclease analysis [REA] BI), several typing methodologies are used for C. difficile. Each methodology offers its own advantages and disadvantages, and several comparisons between some of these methods have been published (32-39), but no consensus exists on a standardized optimal typing method (40,41). Phenotypic typing methodologies rarely used by most modern laboratories include serology (42), plasmid profiling (39), bacteriophage-bacteriocin typing (43), and pyrolysis mass spectrometry (44). PFGE has remained a widely popular method for typing C. difficile strains for over 20 years (41), partially due to its applicability against a wide range of other bacterial pathogens. This method discriminates strains based on polymorphisms at restriction endonuclease sites across the organism’s genomic DNA that result in differences in DNA fragment lengths seen after electrophoresis. However, it remains a labor-intensive, low-throughput method that requires several days to produce results (35,45). PFGE patterns and the terminology used to describe them can vary between laboratories, making it difficult to compare results for determining strain relatedness. Furthermore, some researchers have reported that a subset of C. difficile isolates are untypeable by PFGE, although they remain typeable by other methods (32). PCR ribotyping has been a popular and sensitive method of strain typing, first described in 1993 (46) and popularized after methodological modifications described by O’Neill et al. (47). It requires the PCR-based amplification of the 16S-to-23S intergenic spacer region of rDNA gene. As the C. difficile genome has several non-identical copies of rDNA gene, this method produces amplicons of various lengths that can be separated by gel electrophoresis. As practiced in the United Kingdom Anaerobe Reference Unit since 1995, at least 116 distinct PCR ribotypes have been recognized in their collection of over 3,000 isolates (41). Compared to PFGE, PCR ribo© 2008 Elsevier
typing has similar discriminatory power and provides faster results but produces patterns that are more difficult to interpret (32). REA is an alternative method for typing C. difficile isolates. Similar to PFGE, genomic DNA is digested by a restriction endonuclease and the resulting fragments are separated by gel electrophoresis (33). It has been demonstrated to be a highly discriminatory and reproducible method (36), although its similarity to PFGE extends to its labor-intensiveness and difficulty in simultaneously processing large numbers of samples. The subjective interpretation of REA patterns often requires comparison to reference strains on the same gel, which limits the ability to match results between different laboratories (48). Toxinotyping has been developed and popularized by Rupnik et al. (49). It currently separates C. difficile isolates into 28 major toxinotypes based on polymorphisms in amplified fragments of the toxin genes tcdA and tcdB. It offers the unique advantage of combining strain typing with characterization of a known virulence factor in one method. Toxinotyping and PCR ribotyping have been found to correlate well in one comparison of 123 isolates (50). One frequent shortcoming of gelbased typing methodologies is their poor reproducibility between laboratories. Determining the DNA sequence of genes, non-coding regions, or even entire genomes offers a solution to this problem. The first genome sequence of C. difficile was published in 2006 by Sebaihia et al. (51). The strain chosen for sequencing, 630, was isolated from a hospitalized patient in Switzerland in 1982 and was resistant to multiple antibiotics and associated with severe disease. However, it was not representative of the NAP1 strain, lacking several of its characteristic genetic markers, such as functional binary toxin genes and deletions in tcdC (52). A notable finding in this strain was that mobile genetic elements, such as integrated bacteriophages and insertion elements, occupied 11% of its genome (51). Six more C. difficile genomes, including current and historic NAP1 isolates, have been submitted in draft form to NCBI by a Canadian group (52). Com0196-4399/00 (see frontmatter)
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parative analysis of these isolates have begun to define genetic diversity within and between strains, producing a set of open reading frames that discriminate NAP1 from non-NAP1 strains and could be used to improve nucleic acid amplification-based assays. Multi-locus sequence typing (MLST) characterizes isolates through comparing sequences of several housekeeping genes (53). When used against a group of 72 varied C. difficile isolates, it produced 34 different sequence types that correlated well with the presence or absence of genes for toxins A and B but did not recognize a distinct hypervirulent subpopulation (54). A subsequent analysis by the same group determined that MLST of virulence genes instead of housekeeping genes yielded higher discriminatory power (55). Multi-locus variable tandem repeat analysis is a recently developed method that appears to offer remarkably high discriminatory power. It requires amplification and sequencing of short nucleotide tandem-repeat units; one study found that its discriminatory power was equal to that of REA, but it had better throughput, with 12 samples giving final results after 36 hours (48). A recent analysis was able to detect 13 clusters within a group of 28 NAP1 isolates, suggesting a high resolution that could assist epidemiologic investigations (56).
Clinical Diagnostics Numerous methods presently exist for the diagnosis of CDAD by detecting C. difficile and/or its toxins, including bacterial culture, cell culture cytotoxicity assays, enzyme-linked immunoassays (EIAs), and nucleic acid amplification of specific gene fragments. Direct culture of stool specimens for C. difficile has limited applicability for routine diagnosis, as it requires a laboratory with anaerobic culturing facilities and is highly sensitive but non-specific unless used in conjunction with a method for detection of toxin production (57). However, it has been suggested that culture may be useful in certain circumstances: when clinical suspicion remains high despite a negative cytotoxicity assay, when strain typing and susceptibility testing may be required for epidemiological studies, or when new diagnostic assays need to be compared to existing methods (58). 90
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Tissue culture cytotoxicity assay (TCCA), with or without neutralization, is often considered the gold standard diagnostic test for CDAD. However, two-step methods combining culture with TCCA may challenge TCCA alone for gold standard status, as the former has been found to detect 15 to 23% more toxigenic C. difficile isolates (58,59). TCCA allows detection of both toxin A+/B+ strains as well as the toxin A– /B+ variants that have been the cause of several outbreaks (60-62). Furthermore, differences in cytopathic effect seen in TCCA have been correlated with some toxin variant strains (62-65), allowing early recognition of a potential outbreak. However, it requires 48 to 72 hours before final results and necessitates the effort and cost involved in purchasing or maintaining a tissue culture line. EIA has become an increasingly popular method for detection of C. difficile in recent years, and currently ranks as the most popular diagnostic test used by laboratories in America and Europe (66,67). Advantages include its ease of use, rapid turnaround time, and ability to produce results on batches of samples (68), although the cost per test remains a concern for laboratories that process many samples (69). Low sensitivity for toxin detection is a concern with many kits (70), although protocols that use toxin-directed EIA as a confirmatory method following a more sensitive C. difficile antigen-targeted screening test can address this concern (58). The target antigen in these assays is the enzyme glutamate dehydrogenase. EIAs are most specific when they detect a combination of targets; detection of toxin A alone risks missing toxin A– /B+ strains that have caused severe disease in several outbreaks (68), while detection of glutamate dehydrogenase alone does not discriminate between toxigenic and non-toxigenic isolates. PCR-based detection of gene targets specific for C. difficile has been more popular as a research tool than as a clinical diagnostic assay. Targets have included 16s rDNA gene, toxins A and B, other genes in the pathogenicity locus PaLoc, and binary toxin. Realtime PCR protocols for detection of C. difficile from clinical stool specimens have been developed (71,72). An observational validation study involving 1,368 stool specimens determined that © 2008 Elsevier
real-time PCR had greater sensitivity than EIA combined detection of toxins A and B (73), while a prospective multicenter study determined that real-time PCR had the highest concordance with TCCA (72).
Prevention The cornerstones of CDAD prevention remain infection control practices and judicious antimicrobial use. Standard infection control practices include handwashing, barrier precautions, and individual isolation with private washrooms, as described in previously published guidelines (74). Handwashing practices have been the subject of ongoing studies, with conflicting findings on the contribution of alcohol-based handrubs to the incidence of CDAD within facilities (75,76). Experimental evidence recently presented suggests that soap and water is superior to alcohol rubs or antiseptic wipes for the removal of C. difficile by handwashing (77). However, the use of alcohol-based hand rinses has not been associated with an increase in CDAD incidence (78). Other preventative strategies exist, including administration of probiotics (79), development of toxin-based vaccines (80), and co-administration of therapeutic agents for CDAD when other antimicrobials are being used. Of these, probiotics have been the most researched in several smaller studies, but systematic reviews and meta-analyses have produced conflicting results that are described in the section on nonantimicrobial therapeutics below. Prospective evidence for the remaining strategies is currently lacking, although vaccine trials are in the planning stages.
Therapeutics – Antimicrobials Standard therapy for CDAD is oral vancomycin or oral metronidazole. Although only vancomycin is currently approved by the FDA for this purpose, treatment guidelines and clinicians have usually supported the preferential use of metronidazole due to its low cost, perceived high efficacy, and concerns over vancomycin creating selective pressure favoring development of resistance in other nosocomial pathogens (e.g., enterococci) (81). Early comparative trials described equally high efficacy rates with both agents (82,83), although these trials lacked information on clinical disease severity and Clinical Microbiology Newsletter 30:12,2008
occurred prior to the current era of increased disease severity and frequency. One retrospective trial described a 71% rate of resolution of diarrhea within 6 days when metronidazole was used alone, with greater illness severity predictive of treatment failure (84). A recent comparison of these antimicrobials concluded that vancomycin was superior to metronidazole in severe CDAD, with clinical cure rates of 97% versus 76%, respectively (85). Similar findings were reported from the first phase III trial of tolevamer, which included metronidazole and vancomycin as direct, head-to-head comparators (86). In this trial, vancomycin was significantly superior to metronidazole (84.8% vs. 64.9%, P < 0.04) for patients with severe CDAD. Risk of recurrent disease has been found to be similar in both antimicrobials. The phase III tolevamer trial measured a recurrence risk of 23.4% for vancomycin and 27.1% for metronidazole, rates similar to those determined by a systematic review (85). However, one study in Quebec described higher relapse rates from metronidazole therapy than from vancomycin (15). Dosing schedules for both agents vary widely; a typical regimen for oral vancomycin is 125 mg four times daily, and a typical regimen for oral metronidazole is 250 mg four times daily. Higher doses of both agents are frequently used in more severe cases, although definitive proof of increased efficacy is lacking. The oral route for these antimicrobials is preferred, but for patients incapable of taking these medications orally, options include administration via nasogastric tube, intravenous metronidazole, and vancomycin retention enemas. Intravenous metronidazole has been demonstrated to produced high intracolonic levels of metronidazole in inflamed colonic tissue (87), while oral vancomycin achieves high intra-luminal levels due to lack of absorption (88). Several case reports and case series of intracolonic vancomycin delivered by enema (89, 90) or colonoscope (91) have claimed efficacy, but large-scale trials have not been performed. Other antimicrobial agents have been tested for efficacy, often in smaller trials lacking stratification for disease severity and typing of the causal C. difficile strains. A recent update of the Cochrane systematic review on C. difficile therapy Clinical Microbiology Newsletter 30:12,2008
concluded that there were no clear advantages to any one antimicrobial therapy for C. difficile (92), although the two most conclusive studies demonstrating superiority of vancomycin (85, 86) were not included in this analysis, and several abstracts from recent meetings were also not reviewed. A poorly absorbed oral antimicrobial that achieves high intraluminal concentrations, rifaximin has demonstrated an 89% efficacy rate and a 10% recurrence rate in an open-label study of 19 patients (93). It has also been shown in one case series of eight patients to be beneficial for treatment of recurrent CDAD (94). It should be noted that one of the patients required two courses of rifaximin for clinical cure and was subsequently found to be colonized with a rifaximinresistant isolate of C. difficile. Another survey of several hundred isolates from three sources found 18 strains resistant to rifaximin (95). Although treatment of CDAD is an off-label use of rifaximin, its minimal effects on gut flora (96) make it an intriguing potential therapeutic tool for the management of this challenging clinical problem, although the discovery of resistant strains is disquieting. The anti-parasitic agent nitazoxanide was claimed to be as efficacious as metronidazole in one randomized noninferiority trial (97), although the study has been questioned for its low statistical power and high exclusion rate (98). Ramoplanin, a glycolipodepsipeptide active against gram-positive bacteria (99), showed clinical cure rates for CDAD of 83 to 85%, comparable to the vancomycin patients in the study, but resulted in recurrence rates of 22 to 26% which were higher (but not statistically significant) than the 17% recurrent rate in the vancomycin patients (100). Another novel non-absorbable drug, OPT-80 (also called PAR-101), is an 18-member macrocyclic antibiotic with potent in vitro activity against C. difficile and poor inhibitory activity against gram-negative and anaerobic stool flora (101). A phase 2 open-label study showed 100% clinical effectiveness at the higher dose used, with recurrence in only 6% of patients (102). A large phase III multinational comparative study of OPT-80 and vancomycin is currently under way. © 2008 Elsevier
Therapeutics – Non-antimicrobials Tolevamer, a toxin-binding resin, showed some early promise as a novel therapeutic agent (103). However, a phase III trial found lower clinical cure rates than vancomycin and metronidazole (86). Subgroup analysis described a lower rate of recurrence in the tolevamer arm, but the disease severity of patients in this arm may have been dissimilar to that of the comparators. Further data on tolevamer will come from a second phase III trial currently nearing completion. Intravenous immunoglobulin (IVIG) is frequently used in patients with severe or refractory CDAD. One retrospective review of 14 cases between November 2003 and December 2005 found a 64% cure rate in patients who had received multiple previous courses of metronidazole or vancomycin, including six of eight patients with severe CDAD but zero of two patients with underlying hematological malignancy (104). There were no apparent adverse effects from IVIG therapy. Similar findings were reported in a series of five cases from the United Kingdom (105). Prospective trials of this expensive therapy have not yet been published, and the optimal dose, dosing schedule, and predictors of treatment success and failure remain undetermined. Probiotics have been frequently studied for prevention and treatment of CDAD, but the defining hallmark of trials in this field has been variability. Commonly used species include Lactobacillus acidophilus, L. bulgaricus, L. plantarum 299v, L. rhamnosus GG, and Saccharomyces boulardii, alone or in combination; dosing regimens differ between study protocols; finally, the results of these trials have been inconsistent. One randomized, placebo-controlled study of S. boulardii found it effective for treating recurrent CDAD but ineffective for treating initial episodes (106). Trials involving probiotics for prevention of antibiotic-associated diarrhea and treatment of CDAD have been pooled in one meta-analysis (107), but the validity of meta-analysis for such varied studies has been challenged (108). A systematic review of probiotics for CDAD concluded that “studies… provide insufficient evidence for the routine clinical use of probiotics to prevent or treat CDAD” (79). A 0196-4399/00 (see frontmatter)
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recent prospective trial showed effectiveness of probiotic-containing product to prevent CDAD (109), but criticisms exist of the study’s methodology and findings (110) Restoration of fecal flora has attracted attention for its novelty but deserves some consideration for use in recurrent or refractory CDAD. Several case series have documented impressive efficacy rates of 94 to 100% when enteral “stool transplants” were used in patients who had failed multiple courses of conventional therapy (111-114). Donor stool is the most common source of fecal flora, although it poses challenges, including screening for pathogens, storing and manipulating large volumes of stool, and preparation of the stool for transplant. One group avoided these difficulties by using enteral instillation of a slurry of 10 species of intestinal flora grown in vitro, which demonstrated clinical success in all five patients for whom it was used (114). Surgery remains an important therapy for treatment of severe CDAD. Total colectomy appears to be the procedure of choice, as subtotal colectomies have been associated with substantially higher mortality rates. However, there remain no well-defined criteria for determining which patients would benefit most from surgery or at what point in the course of their disease patients should proceed to surgery. One retrospective case series recommended surgery for patients with signs of toxicity, peritonitis, or intestinal perforation (115). Other criteria, including the need for vasopressors along with patient age of >74 years, APACHE score of >27, hyperlactatemia, and leukocytosis in the range of 20,000 to 50,000 cells/mm3, were presented in conference form but await validation (116).
Conclusions The emergence of the NAP1 strain of C. difficile has illustrated how suddenly a disease can change due to alterations in the pathogen and environment. By necessity, this new wave of CDAD has required improved tools for diagnosis, prognosis, and treatment. The international research community has started to provide some of these tools, such as more sensitive screening protocols, better understanding of pathogenicity mechanisms and risk factors for severe disease, and the relative efficacies of 92
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conventional therapeutic agents. Some important problems remain, including determining optimal strategies for prevention of disease, prediction and management of severe CDAD, and the treatment of recurrent disease. References 1. Archibald, L.K., S.N. Banerjee, and W.R. Jarvis. 2004. Secular trends in hospital-acquired Clostridium difficile disease in the United States, 1987-2001. J. Infect. Dis. 189:1585-1589. 2. Ricciardi, R. et al. Increasing prevalence and severity of Clostridium difficile colitis in hospitalized patients in the United States. Arch. Surg. 2007. 142:624-631. 3. Redelings, M.D., F. Sorvillo, and L. Mascola. 2007. Increase in Clostridium difficile-related mortality rates, United States, 1999-2004. Emerg. Infect. Dis. 13:1417-1419. 4. Centers for Disease Control and Prevention. 2007. Data and statistics about Clostridium difficile infections. http:// www.cdc.gov/ncidod/dhqp/id_Cdiff_ data.html. 5. McDonald, L.C. et al. 2005. An epidemic, toxin gene-variant strain of Clostridium difficile. N. Engl. J. Med. 353:2433-2441. 6. Tan, E.T. et al. 2007. Clostridium difficile-associated disease in New Jersey hospitals, 2000-2004. Emerg. Infect. Dis. 13:498-500. 7. Kyne, L. et al. 2002. Health care costs and mortality associated with nosocomial diarrhea due to Clostridium difficile. Clin. Infect. Dis. 34:346-353. 8. Chernak, E. et al. 2005. Severe Clostridium difficile-associated disease in populations previously at low risk — four states, 2005. MMWR Morb. Mortal. Wkly. Rep. 54:1201-1205. 9. Miller, M.A. et al. 2002. Morbidity, mortality, and healthcare burden of nosocomial Clostridium difficile-associated diarrhea in Canadian hospitals. Infect. Contr. Hosp. Epidemiol. 23:137-140. 10. Eggertson, L. and B. Sibbald. 2004. Hospitals battling outbreaks of C. difficile. CMAJ 171:19-21. 11. Weiss, K. et al. 2007. Clostridium difficile-associated diarrhoea rates and global antibiotic consumption in five Quebec institutions from 2001 to 2004. Int. J. Antimicrob. Agents 30:309-314. 12. Loo, V.G. et al. 2005. A predominantly clonal multi-institutional outbreak of Clostridium difficile-associated diarrhea with high morbidity and mortality. N. Engl. J. Med. 353:2442-2449.
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Dis. 35:690-696. 90. Surowiec, D. et al. 2006. Past, present, and future therapies for Clostridium difficile-associated disease. Ann. Pharmacother. 40:2155-2163. DOI 10.1345/aph.1H332. 91. Shetler, K. et al. 2001. Decompressive colonoscopy with intracolonic vancomycin administration for the treatment of severe pseudomembranous colitis. Surg. Endosc. 15:653-659. 92. Nelson, R. 2007. Antibiotic treatment for Clostridium difficile-associated diarrhea in adults. Cochrane Database Syst. Rev. Issue 3, Article no. CD004610. DOI 10.1002/14651858.CD004610.pub3. 93. Berenbaum, P.L. 2006. Oral rifaximin in treatment of Clostridium difficile-associated diarrhea. Am. J. Gastroenterol. 101:S199. 94. Johnson, S. et al. 2007. Interruption of recurrent Clostridium difficile-associated diarrhea episodes by serial therapy with vancomycin and rifaximin. Clin. Infect. Dis. 44:846-848. 95. Galang, M.A. et al. 2007. Rifampin susceptibility by agar dilution and Etest predicts susceptibility to rifaximin in Clostridium difficile, abstr. no. K-425. Abstr. 47th Intersci. Conf. Antimicrob. Agents Chemother., Chicago, IL, 17-20 September, 2007. American Society for Microbiology, Washington, D.C. 96. DuPont, H.L. et al. 2005. A randomized, double-blind, placebo-controlled trial of rifaximin to prevent travelers’ diarrhea. Ann. Intern. Med. 142:805-812. 97. Musher, D.M. et al. 2006. Nitazoxanide for the treatment of Clostridium difficile Colitis. Clin. Infect. Dis. 43:421-427. 98. Young, J.D. et al. 2007. Nitazoxanide versus metronidazole for Clostridium difficile-associated colitis. Clin. Infect. Dis. 44:152. 99. Farver, D.K., D.D. Hedge, and S.C. Lee. 2005. Ramoplanin: a lipoglycodepsipeptide antibiotic. Ann. Pharmacother. 39:863-868. 100. Leach, T., J. Pullman, and J. Prieto. 2004. Ramoplanin vs. vancomycin in the treatment of Clostridium difficile diarrhea: a phase 2 study, abstr. no. K-985a. Abstr. 44th Intersci. Conf. Antimicrob. Agents Chemother., Washington, DC., 30 October to 4 November, 2004. American Society for Microbiology, Washington, DC. 101. Ackermann, G. et al. 2004. In vitro activity of OPT-80 against Clostridium difficile. Antimicrob. Agents Chemother. 48:2280-2282. 102. Louie, T. et al. 2005. Safety, pharmacokinetics and outcomes of PAR-101 in
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Clinical and Epidemiological Aspects of Clostridium difficile Matthew T. Oughton, MD, FRCPC1 and Mark A. Miller, MD, FRCPC,1,2,3 1Faculty of Medicine, McGill University, 2 Division of Clinical Microbiology and 3Division of Infectious Diseases, Department of Medicine, SMBD-Jewish General Hospital, Montreal, Quebec, Canada
Abstract Clostridium difficile-associated disease (CDAD) has increased in frequency and severity throughout North America and Europe over the last 5 years, largely due to the emergence of the NAP1 epidemic strain. This transformation of a formerly mild disease into one that can cause severe morbidity and mortality within a few days has challenged our entire approach to this serious infection. Institutions require accurate and rapid diagnostics for early detection of cases and possible outbreaks in order to initiate specific therapy and implement effective infection control. The optimal hand hygiene techniques, barrier methods and environmental cleaning practices that would diminish transmission remain uncertain. Clinicians need reliable research that can pinpoint the most important factors determining severity of disease and relapse. Epidemiologic and molecular analyses are vital in order to understand the local and international transmission of this disease, as well as its recent change in pathogenicity. As well, further examination of this infection is crucial in order to find effective prophylactic maneuvers and optimal therapies. This review discusses the changing epidemiology of CDAD across North America and internationally, as well as the common diagnostic methods and molecular typing tools for this pathogen. Finally, the current evidence supporting conventional, novel, and non-antimicrobial preventative and therapeutic options is examined.
Introduction A new era for Clostridium difficile began early this millennium, causing problems for patients and challenges for health care workers that continue to the present day. Symptomatic disease caused by C. difficile has been called “C. difficile-associated diarrhea,” “C. difficile-associated disease” (both abbreviated as “CDAD”), or “C. difficile infection.” What had been considered largely a “nuisance disease,” causing mild diarrhea and responding to withdrawal of the inciting antibiotic or a short course of metronidazole, turned quickly into epidemics that closed down hospital wards, left
Mailing Address: Mark A. Miller, M.D., FRCPC, SMBD-Jewish General Hospital, 3755 Cote-Ste-Catherine Road, Suite G-139, Montreal, Quebec, Canada H3T 1E2. Tel: 514-340-8294. Fax: 514-340-7546. E-mail: [email protected]
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patients in intensive care facing total colectomies, and dramatically illustrated the importance of basic infection control precautions. This rapidly evolving epidemiology gave new importance to some lingering clinical questions: “What factors have driven this sudden change in disease frequency and severity?” Which patients would benefit from surgical intervention?” “What is the optimal therapy?” “How should recurrent disease be managed?” This paper will review the data that has begun to provide some answers to these questions.
Epidemiology
rise in regional and national epidemiologic studies from countries across North America, Europe, and southeastern Asia. These outbreaks have been largely, although not exclusively, driven by the newly recognized North American pulsed-field type 1 (NAP1) strain, alternately known as ribotype 027, restriction endonuclease type BI, toxinotype III, or the “hypervirulent strain” (depending on the typing methodology and nomenclature used), which carries (i) genetic mutations in the tcdC toxin regulator gene, (ii) binary toxin genes, and (iii) fluoroquinolone resistance mutations.
Prior to 2001, comprehensive epidemiologic studies of C. difficile and CDAD were limited, as might be expected for a disease lacking mandatory reporting due to its low severity and inexpensive treatment. The current era of increased CDAD frequency and severity has prompted a concomitant © 2008 Elsevier
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United States CDAD incidence across America has been increasing, as seen in analyses of two large national medical databases. In hospitals participating in the National Nosocomial Infections Surveillance System from 1987 to 2001 (1), CDAD incidence gradually increased in the intensive care units (ICUs) of large (>500-bed) hospitals. With ICU data excluded, incidence rates increased only in smaller (<250-bed) hospitals, particularly on medical wards; the cause of this apparent discrepancy remains unclear. A recent cohort analysis of patients from the Nationwide Inpatient Sample, representing 1,000 hospitals across 35 states, found a doubling of the C. difficile colitis incidence rate from 261 cases per 100,000 discharged patients in 1993 to 546 cases per 100,000 discharged patients in 2003 (2); half of that increase occurred in the final 2 years of the study. Most recently, population-based estimates of C. difficile mortality rates rose more than fourfold, from 5.7 per million population in 1999 to 23.7 per million population in 2004 (3). The presence of the NAP1 strain had been identified in at least 27 states as of April 2007 (4) and has been reported as the main cause of out-breaks in several states (5,6). The impacts of CDAD on individuals and healthcare institutions in America are considerable. One prospective follow-up of 271 patients at a teaching hospital in Boston determined that hospital-acquired CDAD resulted in a median 54% increase in hospital costs (an additional $3,669) and a median 3.6-day-longer hospital admission compared to patients without CDAD (7). It should be noted that this study used data from patients with predominantly mild to moderate CDAD admitted from January to May 1998; thus, it likely
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underestimates costs and lengths of stay due to the more severe disease caused by NAP1 and related strains. A recent summary of case reports across four states identified severe CDAD in community-dwelling patients and peripartum women, groups usually considered as low risk for CDAD (8); however, the C. difficile strains in these cases were not typed, and therefore, the cases were not necessarily due to the NAP1 strain.
Canada The baseline for CDAD frequency, severity, and cost to the healthcare system in Canada was established in the Canadian Nosocomial Infection Surveillance Program (CNISP) survey of 2,062 patients from 19 institutions in eight provinces during 1997 (9). Thirteen percent of all inpatients tested for diarrhea met the case definition for CDAD, yielding an incidence of 5.9 cases per 1,000 patient admissions. Complications occurred in 8% of these patients, with 1.5% of all mortality being attributed directly or indirectly to CDAD. Increases in CDAD frequency and mortality were first widely reported in mid-2004 (10), although recent studies have retrospectively identified increases from as early as December 2002 (11). A study of 12 Quebec hospitals during the first half of 2004 (12) determined the incidence to be 22.5 per 1,000 patient admissions, with an attributable mortality rate of 6.9%; both rates represented approximately fourfold increases compared to historic rates determined by the CNISP study. The mortality burden varied directly with patient age, increasing from 1.2% in patients aged 41 to 50 to 10% in patients aged 81 to 90 and 14% in patients older than 90. Although the NAP1 strain predominated in this study, case severity was significantly associated not with strain type, but rather with the presence
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of two putative virulence factors: binary toxin and a partial deletion in the negative toxin regulator gene tcdC. A later prospective study involving 88 Quebec hospitals found that severe disease was twice as frequent in patients infected by strains possessing these two virulence factors (13). A fivefold increase in CDAD incidence was described in a population-based retrospective study from one teaching hospital in Quebec over the 12-year period from 1991 to 2003 (14). This study found a concomitant doubling in the proportion of CDAD complications (death, toxic megacolon, intestinal perforation, colectomy, or shock requiring vasopressors); the increases in incidence and complication rates largely occurred in the last year of the study. The same group subsequently reported that the risk of recurrent CDAD at 60 days more than doubled, from 21% during 1991 to 2002 to over 47% in 2003 to 2004 (15). These findings demonstrated that CDAD in Quebec had suddenly and dramatically increased in severity, supporting the argument that emergence of a highly virulent strain or strains was largely responsible. Another survey across three Canadian provinces documented the absence of C. difficile ribotype 027 in Quebec isolates during 2000 to 2001, followed by its abrupt rise 3 years later (16). A follow-up CNISP survey of 34 hospitals across nine provinces during November 2004 to April 2005 revealed an unchanged overall mean CDAD incidence at 6.4 per 10,000 patient days (17). However, the incidence in Quebec, at 11.9 per 10,000 patient days, remained almost double the historic rate.
Europe and Asia The recent European experience with CDAD has largely followed the patterns seen in North America. One
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recent review stated that C. difficile was responsible for twice as many deaths as methicillin-resistant Staphylococcus aureus in the United Kingdom during 2003 (18). The same article claimed the attributable mortality rate had increased 2.3-fold from 1999 to 2004. The NAP1 strain has been recognized as the cause of outbreaks across six European countries (United Kingdom, Netherlands, Belgium, France, Austria, and Ireland) and has been detected sporadically in at least six more (Switzerland, Luxembourg, Poland, Denmark, Sweden, and Finland) (19,20). The exact origin of the NAP1 strain is uncertain, although historic examples of the strain appear in at least two large European collections. It was identified in a Swedish strain collection of isolates dating from as early as 1997 (19), and it is stored as isolate CD 196 (21) in a reference bank of the Institut Pasteur, originally isolated in France during 1984 (22) and the isolate in which binary toxin was first reported (23). The prevalence of the NAP1 strain varies widely by country; a survey of 149 randomly selected isolates collected throughout southeast Scotland from August to October 2005 found no ribotype 027 isolates (24). A frequent trend toward high frequency of fluoroquinolone resistance in C. difficile isolates has appeared in reports from the United Kingdom (25), The Netherlands (26), Spain (27), and Poland (28). There is less epidemiologic information on C. difficile and CDAD in Asian countries. One survey of isolates collected in Japan, Korea, and Indonesia found a wide variety of toxinotypes, with toxinotype 0 predominating (29). An analysis of 148 isolates from one Japanese teaching hospital identified an epidemic strain (PCR ribotype smz) responsible for outbreaks in multiple hospitals, along with a single isolate of NAP1 collected in 2001 that was fluoroquinolone susceptible and associated with community onset disease (30). The NAP1 isolate was again detected in Japan from a patient hospitalized in March 2005 (31). The authors noted that the isolate was also susceptible to fluoroquinolones, which may have explained its absence from outbreaks in Japanese healthcare facilities. Clinical Microbiology Newsletter 30:12,2008
Molecular Epidemiology As illustrated by the long list of names sometimes assigned to the virulent strain responsible for numerous outbreaks (ribotype 027/toxinotype III/pulsed-field gel electrophoresis [PFGE] pattern NAP1/restriction endonuclease analysis [REA] BI), several typing methodologies are used for C. difficile. Each methodology offers its own advantages and disadvantages, and several comparisons between some of these methods have been published (32-39), but no consensus exists on a standardized optimal typing method (40,41). Phenotypic typing methodologies rarely used by most modern laboratories include serology (42), plasmid profiling (39), bacteriophage-bacteriocin typing (43), and pyrolysis mass spectrometry (44). PFGE has remained a widely popular method for typing C. difficile strains for over 20 years (41), partially due to its applicability against a wide range of other bacterial pathogens. This method discriminates strains based on polymorphisms at restriction endonuclease sites across the organism’s genomic DNA that result in differences in DNA fragment lengths seen after electrophoresis. However, it remains a labor-intensive, low-throughput method that requires several days to produce results (35,45). PFGE patterns and the terminology used to describe them can vary between laboratories, making it difficult to compare results for determining strain relatedness. Furthermore, some researchers have reported that a subset of C. difficile isolates are untypeable by PFGE, although they remain typeable by other methods (32). PCR ribotyping has been a popular and sensitive method of strain typing, first described in 1993 (46) and popularized after methodological modifications described by O’Neill et al. (47). It requires the PCR-based amplification of the 16S-to-23S intergenic spacer region of rDNA gene. As the C. difficile genome has several non-identical copies of rDNA gene, this method produces amplicons of various lengths that can be separated by gel electrophoresis. As practiced in the United Kingdom Anaerobe Reference Unit since 1995, at least 116 distinct PCR ribotypes have been recognized in their collection of over 3,000 isolates (41). Compared to PFGE, PCR ribo© 2008 Elsevier
typing has similar discriminatory power and provides faster results but produces patterns that are more difficult to interpret (32). REA is an alternative method for typing C. difficile isolates. Similar to PFGE, genomic DNA is digested by a restriction endonuclease and the resulting fragments are separated by gel electrophoresis (33). It has been demonstrated to be a highly discriminatory and reproducible method (36), although its similarity to PFGE extends to its labor-intensiveness and difficulty in simultaneously processing large numbers of samples. The subjective interpretation of REA patterns often requires comparison to reference strains on the same gel, which limits the ability to match results between different laboratories (48). Toxinotyping has been developed and popularized by Rupnik et al. (49). It currently separates C. difficile isolates into 28 major toxinotypes based on polymorphisms in amplified fragments of the toxin genes tcdA and tcdB. It offers the unique advantage of combining strain typing with characterization of a known virulence factor in one method. Toxinotyping and PCR ribotyping have been found to correlate well in one comparison of 123 isolates (50). One frequent shortcoming of gelbased typing methodologies is their poor reproducibility between laboratories. Determining the DNA sequence of genes, non-coding regions, or even entire genomes offers a solution to this problem. The first genome sequence of C. difficile was published in 2006 by Sebaihia et al. (51). The strain chosen for sequencing, 630, was isolated from a hospitalized patient in Switzerland in 1982 and was resistant to multiple antibiotics and associated with severe disease. However, it was not representative of the NAP1 strain, lacking several of its characteristic genetic markers, such as functional binary toxin genes and deletions in tcdC (52). A notable finding in this strain was that mobile genetic elements, such as integrated bacteriophages and insertion elements, occupied 11% of its genome (51). Six more C. difficile genomes, including current and historic NAP1 isolates, have been submitted in draft form to NCBI by a Canadian group (52). Com0196-4399/00 (see frontmatter)
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parative analysis of these isolates have begun to define genetic diversity within and between strains, producing a set of open reading frames that discriminate NAP1 from non-NAP1 strains and could be used to improve nucleic acid amplification-based assays. Multi-locus sequence typing (MLST) characterizes isolates through comparing sequences of several housekeeping genes (53). When used against a group of 72 varied C. difficile isolates, it produced 34 different sequence types that correlated well with the presence or absence of genes for toxins A and B but did not recognize a distinct hypervirulent subpopulation (54). A subsequent analysis by the same group determined that MLST of virulence genes instead of housekeeping genes yielded higher discriminatory power (55). Multi-locus variable tandem repeat analysis is a recently developed method that appears to offer remarkably high discriminatory power. It requires amplification and sequencing of short nucleotide tandem-repeat units; one study found that its discriminatory power was equal to that of REA, but it had better throughput, with 12 samples giving final results after 36 hours (48). A recent analysis was able to detect 13 clusters within a group of 28 NAP1 isolates, suggesting a high resolution that could assist epidemiologic investigations (56).
Clinical Diagnostics Numerous methods presently exist for the diagnosis of CDAD by detecting C. difficile and/or its toxins, including bacterial culture, cell culture cytotoxicity assays, enzyme-linked immunoassays (EIAs), and nucleic acid amplification of specific gene fragments. Direct culture of stool specimens for C. difficile has limited applicability for routine diagnosis, as it requires a laboratory with anaerobic culturing facilities and is highly sensitive but non-specific unless used in conjunction with a method for detection of toxin production (57). However, it has been suggested that culture may be useful in certain circumstances: when clinical suspicion remains high despite a negative cytotoxicity assay, when strain typing and susceptibility testing may be required for epidemiological studies, or when new diagnostic assays need to be compared to existing methods (58). 90
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Tissue culture cytotoxicity assay (TCCA), with or without neutralization, is often considered the gold standard diagnostic test for CDAD. However, two-step methods combining culture with TCCA may challenge TCCA alone for gold standard status, as the former has been found to detect 15 to 23% more toxigenic C. difficile isolates (58,59). TCCA allows detection of both toxin A+/B+ strains as well as the toxin A– /B+ variants that have been the cause of several outbreaks (60-62). Furthermore, differences in cytopathic effect seen in TCCA have been correlated with some toxin variant strains (62-65), allowing early recognition of a potential outbreak. However, it requires 48 to 72 hours before final results and necessitates the effort and cost involved in purchasing or maintaining a tissue culture line. EIA has become an increasingly popular method for detection of C. difficile in recent years, and currently ranks as the most popular diagnostic test used by laboratories in America and Europe (66,67). Advantages include its ease of use, rapid turnaround time, and ability to produce results on batches of samples (68), although the cost per test remains a concern for laboratories that process many samples (69). Low sensitivity for toxin detection is a concern with many kits (70), although protocols that use toxin-directed EIA as a confirmatory method following a more sensitive C. difficile antigen-targeted screening test can address this concern (58). The target antigen in these assays is the enzyme glutamate dehydrogenase. EIAs are most specific when they detect a combination of targets; detection of toxin A alone risks missing toxin A– /B+ strains that have caused severe disease in several outbreaks (68), while detection of glutamate dehydrogenase alone does not discriminate between toxigenic and non-toxigenic isolates. PCR-based detection of gene targets specific for C. difficile has been more popular as a research tool than as a clinical diagnostic assay. Targets have included 16s rDNA gene, toxins A and B, other genes in the pathogenicity locus PaLoc, and binary toxin. Realtime PCR protocols for detection of C. difficile from clinical stool specimens have been developed (71,72). An observational validation study involving 1,368 stool specimens determined that © 2008 Elsevier
real-time PCR had greater sensitivity than EIA combined detection of toxins A and B (73), while a prospective multicenter study determined that real-time PCR had the highest concordance with TCCA (72).
Prevention The cornerstones of CDAD prevention remain infection control practices and judicious antimicrobial use. Standard infection control practices include handwashing, barrier precautions, and individual isolation with private washrooms, as described in previously published guidelines (74). Handwashing practices have been the subject of ongoing studies, with conflicting findings on the contribution of alcohol-based handrubs to the incidence of CDAD within facilities (75,76). Experimental evidence recently presented suggests that soap and water is superior to alcohol rubs or antiseptic wipes for the removal of C. difficile by handwashing (77). However, the use of alcohol-based hand rinses has not been associated with an increase in CDAD incidence (78). Other preventative strategies exist, including administration of probiotics (79), development of toxin-based vaccines (80), and co-administration of therapeutic agents for CDAD when other antimicrobials are being used. Of these, probiotics have been the most researched in several smaller studies, but systematic reviews and meta-analyses have produced conflicting results that are described in the section on nonantimicrobial therapeutics below. Prospective evidence for the remaining strategies is currently lacking, although vaccine trials are in the planning stages.
Therapeutics – Antimicrobials Standard therapy for CDAD is oral vancomycin or oral metronidazole. Although only vancomycin is currently approved by the FDA for this purpose, treatment guidelines and clinicians have usually supported the preferential use of metronidazole due to its low cost, perceived high efficacy, and concerns over vancomycin creating selective pressure favoring development of resistance in other nosocomial pathogens (e.g., enterococci) (81). Early comparative trials described equally high efficacy rates with both agents (82,83), although these trials lacked information on clinical disease severity and Clinical Microbiology Newsletter 30:12,2008
occurred prior to the current era of increased disease severity and frequency. One retrospective trial described a 71% rate of resolution of diarrhea within 6 days when metronidazole was used alone, with greater illness severity predictive of treatment failure (84). A recent comparison of these antimicrobials concluded that vancomycin was superior to metronidazole in severe CDAD, with clinical cure rates of 97% versus 76%, respectively (85). Similar findings were reported from the first phase III trial of tolevamer, which included metronidazole and vancomycin as direct, head-to-head comparators (86). In this trial, vancomycin was significantly superior to metronidazole (84.8% vs. 64.9%, P < 0.04) for patients with severe CDAD. Risk of recurrent disease has been found to be similar in both antimicrobials. The phase III tolevamer trial measured a recurrence risk of 23.4% for vancomycin and 27.1% for metronidazole, rates similar to those determined by a systematic review (85). However, one study in Quebec described higher relapse rates from metronidazole therapy than from vancomycin (15). Dosing schedules for both agents vary widely; a typical regimen for oral vancomycin is 125 mg four times daily, and a typical regimen for oral metronidazole is 250 mg four times daily. Higher doses of both agents are frequently used in more severe cases, although definitive proof of increased efficacy is lacking. The oral route for these antimicrobials is preferred, but for patients incapable of taking these medications orally, options include administration via nasogastric tube, intravenous metronidazole, and vancomycin retention enemas. Intravenous metronidazole has been demonstrated to produced high intracolonic levels of metronidazole in inflamed colonic tissue (87), while oral vancomycin achieves high intra-luminal levels due to lack of absorption (88). Several case reports and case series of intracolonic vancomycin delivered by enema (89, 90) or colonoscope (91) have claimed efficacy, but large-scale trials have not been performed. Other antimicrobial agents have been tested for efficacy, often in smaller trials lacking stratification for disease severity and typing of the causal C. difficile strains. A recent update of the Cochrane systematic review on C. difficile therapy Clinical Microbiology Newsletter 30:12,2008
concluded that there were no clear advantages to any one antimicrobial therapy for C. difficile (92), although the two most conclusive studies demonstrating superiority of vancomycin (85, 86) were not included in this analysis, and several abstracts from recent meetings were also not reviewed. A poorly absorbed oral antimicrobial that achieves high intraluminal concentrations, rifaximin has demonstrated an 89% efficacy rate and a 10% recurrence rate in an open-label study of 19 patients (93). It has also been shown in one case series of eight patients to be beneficial for treatment of recurrent CDAD (94). It should be noted that one of the patients required two courses of rifaximin for clinical cure and was subsequently found to be colonized with a rifaximinresistant isolate of C. difficile. Another survey of several hundred isolates from three sources found 18 strains resistant to rifaximin (95). Although treatment of CDAD is an off-label use of rifaximin, its minimal effects on gut flora (96) make it an intriguing potential therapeutic tool for the management of this challenging clinical problem, although the discovery of resistant strains is disquieting. The anti-parasitic agent nitazoxanide was claimed to be as efficacious as metronidazole in one randomized noninferiority trial (97), although the study has been questioned for its low statistical power and high exclusion rate (98). Ramoplanin, a glycolipodepsipeptide active against gram-positive bacteria (99), showed clinical cure rates for CDAD of 83 to 85%, comparable to the vancomycin patients in the study, but resulted in recurrence rates of 22 to 26% which were higher (but not statistically significant) than the 17% recurrent rate in the vancomycin patients (100). Another novel non-absorbable drug, OPT-80 (also called PAR-101), is an 18-member macrocyclic antibiotic with potent in vitro activity against C. difficile and poor inhibitory activity against gram-negative and anaerobic stool flora (101). A phase 2 open-label study showed 100% clinical effectiveness at the higher dose used, with recurrence in only 6% of patients (102). A large phase III multinational comparative study of OPT-80 and vancomycin is currently under way. © 2008 Elsevier
Therapeutics – Non-antimicrobials Tolevamer, a toxin-binding resin, showed some early promise as a novel therapeutic agent (103). However, a phase III trial found lower clinical cure rates than vancomycin and metronidazole (86). Subgroup analysis described a lower rate of recurrence in the tolevamer arm, but the disease severity of patients in this arm may have been dissimilar to that of the comparators. Further data on tolevamer will come from a second phase III trial currently nearing completion. Intravenous immunoglobulin (IVIG) is frequently used in patients with severe or refractory CDAD. One retrospective review of 14 cases between November 2003 and December 2005 found a 64% cure rate in patients who had received multiple previous courses of metronidazole or vancomycin, including six of eight patients with severe CDAD but zero of two patients with underlying hematological malignancy (104). There were no apparent adverse effects from IVIG therapy. Similar findings were reported in a series of five cases from the United Kingdom (105). Prospective trials of this expensive therapy have not yet been published, and the optimal dose, dosing schedule, and predictors of treatment success and failure remain undetermined. Probiotics have been frequently studied for prevention and treatment of CDAD, but the defining hallmark of trials in this field has been variability. Commonly used species include Lactobacillus acidophilus, L. bulgaricus, L. plantarum 299v, L. rhamnosus GG, and Saccharomyces boulardii, alone or in combination; dosing regimens differ between study protocols; finally, the results of these trials have been inconsistent. One randomized, placebo-controlled study of S. boulardii found it effective for treating recurrent CDAD but ineffective for treating initial episodes (106). Trials involving probiotics for prevention of antibiotic-associated diarrhea and treatment of CDAD have been pooled in one meta-analysis (107), but the validity of meta-analysis for such varied studies has been challenged (108). A systematic review of probiotics for CDAD concluded that “studies… provide insufficient evidence for the routine clinical use of probiotics to prevent or treat CDAD” (79). A 0196-4399/00 (see frontmatter)
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recent prospective trial showed effectiveness of probiotic-containing product to prevent CDAD (109), but criticisms exist of the study’s methodology and findings (110) Restoration of fecal flora has attracted attention for its novelty but deserves some consideration for use in recurrent or refractory CDAD. Several case series have documented impressive efficacy rates of 94 to 100% when enteral “stool transplants” were used in patients who had failed multiple courses of conventional therapy (111-114). Donor stool is the most common source of fecal flora, although it poses challenges, including screening for pathogens, storing and manipulating large volumes of stool, and preparation of the stool for transplant. One group avoided these difficulties by using enteral instillation of a slurry of 10 species of intestinal flora grown in vitro, which demonstrated clinical success in all five patients for whom it was used (114). Surgery remains an important therapy for treatment of severe CDAD. Total colectomy appears to be the procedure of choice, as subtotal colectomies have been associated with substantially higher mortality rates. However, there remain no well-defined criteria for determining which patients would benefit most from surgery or at what point in the course of their disease patients should proceed to surgery. One retrospective case series recommended surgery for patients with signs of toxicity, peritonitis, or intestinal perforation (115). Other criteria, including the need for vasopressors along with patient age of >74 years, APACHE score of >27, hyperlactatemia, and leukocytosis in the range of 20,000 to 50,000 cells/mm3, were presented in conference form but await validation (116).
Conclusions The emergence of the NAP1 strain of C. difficile has illustrated how suddenly a disease can change due to alterations in the pathogen and environment. By necessity, this new wave of CDAD has required improved tools for diagnosis, prognosis, and treatment. The international research community has started to provide some of these tools, such as more sensitive screening protocols, better understanding of pathogenicity mechanisms and risk factors for severe disease, and the relative efficacies of 92
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conventional therapeutic agents. Some important problems remain, including determining optimal strategies for prevention of disease, prediction and management of severe CDAD, and the treatment of recurrent disease. References 1. Archibald, L.K., S.N. Banerjee, and W.R. Jarvis. 2004. Secular trends in hospital-acquired Clostridium difficile disease in the United States, 1987-2001. J. Infect. Dis. 189:1585-1589. 2. Ricciardi, R. et al. Increasing prevalence and severity of Clostridium difficile colitis in hospitalized patients in the United States. Arch. Surg. 2007. 142:624-631. 3. Redelings, M.D., F. Sorvillo, and L. Mascola. 2007. Increase in Clostridium difficile-related mortality rates, United States, 1999-2004. Emerg. Infect. Dis. 13:1417-1419. 4. Centers for Disease Control and Prevention. 2007. Data and statistics about Clostridium difficile infections. http:// www.cdc.gov/ncidod/dhqp/id_Cdiff_ data.html. 5. McDonald, L.C. et al. 2005. An epidemic, toxin gene-variant strain of Clostridium difficile. N. Engl. J. Med. 353:2433-2441. 6. Tan, E.T. et al. 2007. Clostridium difficile-associated disease in New Jersey hospitals, 2000-2004. Emerg. Infect. Dis. 13:498-500. 7. Kyne, L. et al. 2002. Health care costs and mortality associated with nosocomial diarrhea due to Clostridium difficile. Clin. Infect. Dis. 34:346-353. 8. Chernak, E. et al. 2005. Severe Clostridium difficile-associated disease in populations previously at low risk — four states, 2005. MMWR Morb. Mortal. Wkly. Rep. 54:1201-1205. 9. Miller, M.A. et al. 2002. Morbidity, mortality, and healthcare burden of nosocomial Clostridium difficile-associated diarrhea in Canadian hospitals. Infect. Contr. Hosp. Epidemiol. 23:137-140. 10. Eggertson, L. and B. Sibbald. 2004. Hospitals battling outbreaks of C. difficile. CMAJ 171:19-21. 11. Weiss, K. et al. 2007. Clostridium difficile-associated diarrhoea rates and global antibiotic consumption in five Quebec institutions from 2001 to 2004. Int. J. Antimicrob. Agents 30:309-314. 12. Loo, V.G. et al. 2005. A predominantly clonal multi-institutional outbreak of Clostridium difficile-associated diarrhea with high morbidity and mortality. N. Engl. J. Med. 353:2442-2449.
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