Review of the guidelines for complicated skin and soft tissue infections and intra-abdominal infections—are they applicable today?

REVIEW

10.1111/j.1469-0691.2008.02123.x

Review of the guidelines for complicated skin and soft tissue infections and intra-abdominal infections—are they applicable today? M. Caı´nzos Hospital Clı´nico Universitario, Medical School, Santiago de Compostela, Spain

ABSTRACT Difficult-to-treat infections in surgical patients, such as serious skin and soft tissue infections (SSTIs) and complicated intra-abdominal infections (cIAIs), are the cause of significant morbidity and mortality, and carry an economic burden. These surgical site infections are typically polymicrobial infections caused by a plethora of pathogens, which include difficult-to-treat organisms and multiresistant Gram-positive and Gram-negative strains. Optimal management of SSTIs and cIAIs must take into account the presence of resistant pathogens, and depends on the administration of appropriate antimicrobial therapy (i.e. the correct spectrum, route and dose in a timely fashion for a sufficient duration as well as the timely implementation of source control measures). Treatment recommendations from the Infectious Diseases Society of America and the Surgical Infection Society are available for guidance in the management of both of these infections, yet the increased global prevalence of multidrug-resistant pathogens has complicated the antibiotic selection process. Several pathogens of concern include methicillin-resistant Staphylococcus aureus, responsible for problematic postoperative infections, especially in patients with SSTIs, extended-spectrum b-lactamase-producing Gram-negative bacteria, including CTX-M-type-producing Escherichia coli strains, and multidrug-resistant strains of Bacteroides fragilis. New empirical regimens, taking advantage of potent broad-spectrum antibiotic options, may be needed for the treatment of certain high-risk patients with surgical site infections. Keywords Complicated intra-abdominal infections, complicated skin and soft tissue infection, novel antimicrobials, resistant pathogens, treatment guidelines

Clin Microbiol Infect 2008; 14 (Suppl. 6): 9–18

INTRODUCTION Complicated intra-abdominal infections (cIAIs) and serious skin and soft tissue infections (SSTIs) are associated with considerable patient morbidity, mortality and escalating healthcare expenditures, due to the need for additional surgery and antimicrobial therapy, prolonged hospital stay and months of convalescence [1–3]. As such, the significant impact of these infections on patient outcome and survival is an important reason to reassess the management of these infections and the appropriate role of antimicrobial therapy.

Corresponding author and reprint requests: M. Caı´nzos, Department of Surgery, Hospital Clı´nico Universitario, University of Santiago, C ⁄ Vida´n s.n. 15.706 Santiago de Compostela, Spain E-mail: [email protected]

Furthermore, a better means of identifying and treating higher-risk patients with infections caused by potentially multiply antibiotic-resistant bacteria is needed. By definition, cIAI is an infectious process that proceeds beyond the organ that is the source of the infection, and causes either localized peritonitis, also referred to as abdominal abscess, or diffuse peritonitis, depending on whether the patient’s host responses can contain the process within the abdominal cavity [4]. Patients are considered to have complicated (c)SSTIs when there is a need for surgical intervention, if deep soft tissue involvement is suspected or confirmed, and ⁄ or when the patient has a complicating condition such as diabetes mellitus, peripheral vascular disease, or peripheral neuropathy [5]. Both cIAIs and cSSTIs are typically polymicrobial infections caused by a wide range of

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possible pathogens, which include difficult-totreat organisms and multiresistant Gram-positive and Gram-negative strains [6,7]. IAIs are most commonly caused by multiple microorganisms that compose the intestinal flora, such as aerobes and facultative and obligate anaerobes, with Enterobacteriaceae (e.g. Escherichia coli and Klebsiella pneumoniae), enterococci and Bacteroides fragilis being isolated most often [4,7]. It is noteworthy that an increasing number of members of the gastrointestinal flora possess multiple resistance factors that express antimicrobial resistance (e.g. via extended-spectrum b-lactamase (ESBL) production) [8]. Outbreaks due to ESBLproducing E. coli and K. pneumoniae can negatively affect patient outcome, emphasizing the need for the judicious use of antimicrobials in order to minimize the spread of the infectious agents [8]. Likewise, the aetiological agents of cSSTIs also commonly comprise an array of organisms, often with multidrug-resistance phenotypes. A large surveillance study from North America, Europe and Latin America, analysing over 2500 isolates, found that the following organisms were most commonly implicated as causes of cSSTIs: Staphylococcus aureus (39.9%), Pseudomonas aeruginosa (12.1%), E. coli (9.7%), Enterococcus spp. (7.7%), Klebsiella spp. (5.8%), Enterobacter spp. (5.6%), coagulase-negative staphylococci (4.2%), Proteus spp. (3.7%), Streptococcus spp.(2.6%), Acinetobacter spp. (2.2%) and Serratia spp. (2%) [9]. In North America, the prevalence of these pathogens varied slightly: S. aureus, 45.9%; P. aeruginosa, 10.8%; E. coli, 7%; Enterococcus spp., 8.2%; Klebsiella spp., 5.1%; Enterobacter spp., 5.8%; coagulase-negative staphylococci, 3.4%; Proteus spp., 3.2%; Streptococcus spp., 2.7%; Acinetobacter spp., 1.6%; and Serratia spp., 2%. This surveillance study also revealed that the rate of methicillin-resistant S. aureus (MRSA) was 27.2% overall (29% in North America) [9]. The emergence of community-associated MRSA is also alarming, especially in patients with cSSTIs [10]. A retrospective meta-analysis of surveillance studies conducted in Europe confirmed that S. aureus, coagulase-negative staphylococci, E. coli and P. aeruginosa were the most common pathogens associated with cSSTIs ⁄ surgical site infections [11]. Certain patient risk factors, such as a history of intravenous drug use, must also be considered when attempting to predict the possible aetiologies of cSSTIs [12].

Successful management of cIAIs and cSSTIs is dictated, in part, by the likely presence of resistant pathogens, and depends on the administration of adequate antimicrobial therapy, and the timely implementation of source control measures [4,7]. Treatment recommendations are available to guide the clinician in the management of both of these infections [4,13,14]. However, because cSSTIs and cIAIs caused by multidrug-resistant pathogens have become more common over the last decade, alternative empirical treatments not currently outlined in the published guidelines may need to be considered for at-risk patients. The primary purpose of this article is to discuss the impact of surgical site infections, including cSSTIs and cIAIs, on patient outcomes, to review the current treatment guidelines for surgical site infections, and to discuss the current treatment guidelines for cSSTIs and cIAIs in the context of the patterns of emerging resistance in Europe and the potential for monotherapy in empirical regimens. COMPLICATED SKIN AND SOFT TISSUE INFECTIONS ⁄ SURGICAL SITE INFECTIONS Surgically induced soft tissue surgical site infections (SSIs) are typically divided into the following categories: superficial incisional SSIs, deep incisional SSIs, and organ ⁄ space SSIs [15]. Superficial incisional SSIs involve only the subcutaneous space, between the skin and the underlying muscular fascia, and occur within 30 days of the index operation. A deep incisional SSI involves the deep layers of soft tissue (e.g. fascia and muscle) in the incision, and typically occurs within 30 days following the surgical procedure. An organ ⁄ space SSI is similar to a deep incisional SSI, except that it may involve any part of the anatomy (organs or spaces) other than the incision opened during the operation. Assessing the total impact of cSSTIs ⁄ SSIs on patient morbidity and overall outcome is difficult because of incomplete data collection and reporting. A retrospective analysis of reported surgical site infections conducted in Europe attempted to calculate the incidence of these infections [11]. The estimated incidence varied widely, from 1.5% to 20%, suggesting that the true rate of SSTIs is currently unknown and is probably under-reported due to inconsistencies in data

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collection methods and surveillance criteria, and to wide variations in the surgical procedures investigated. The frequency of surgical site infections is clearly related to the category of operation, with clean and low-risk operations having the lowest rate of infection, and contaminated and high-risk operations having greater infection rates [16]. In any event, SSIs carry a significant economic burden, ranging from 1.47 to 19.1 billion euros annually in the European countries [11]. Although the true incidence of cSSTIs per surgical site is unclear, it is well appreciated that these infections are associated with substantial morbidity and can be potentially life-threatening in the surgical patient. A surgical site infection surveillance network implemented in 1997 among general surgical units in northern France which volunteered to participate is a source of important evidence concerning patient outcomes [1]. For 3 months each year, all patients who underwent a surgical procedure were consecutively reviewed for perioperative condition and were traced for outcome with a 30-day follow-up. Among the 38 973 surgical patients included over a 3-year period, 1344 (3.4%) patients developed an SSI, 568 of whom died (1.5%). Organ ⁄ space SSIs and deep incisional SSIs were associated with higher mortality rates (5.7% and 13.2%, respectively) and required re-operation more frequently (44.0% and 53.2%, respectively) than did superficial incisional SSIs (4.2% and 8.6%, respectively). The incidence of mortality associated with surgical site infections was notably high following gastrointestinal procedures. Following 15 665 gastrointestinal procedures, the incidence of surgical site infections was 4.9%, with overall mortality at 2.2% and case-fatality at 7.2%. For all surgical procedures resulting in SSIs, 38% of the deaths in these patients were attributable to infection. cSSTIs are associated with significant underlying disease that often lowers the likelihood of response to treatment. The Infectious Diseases Society of America (IDSA) has recently published several classification schemes and practice guidelines for the diagnosis and management of cSSTIs ⁄ SSIs, including compromised hosts of all age groups [14]. Most patients with cSSTIs ⁄ SSIs will require hospitalization or a prolonged stay, and additional surgical intervention for confirmation of bacterial aetiology and drainage of infected material. Importantly, bacterial culture and susceptibility testing should be undertaken for

patients with signs and symptoms of systemic toxicity, e.g. fever, tachycardia, and hypotension. Aggressive and directed intravenous antimicrobial therapy will be necessary for patients with severe infections. Antibiotic treatment recommendations were based on the surgical site infection category and the location of surgical intervention. SSIs that involve the gastrointestinal tract or the female genital tract can be expected to have a mixed Gram-positive and Gram-negative flora with both facultative and anaerobic organisms. The antimicrobials typically considered to be optimal for treatment of intra-abdominal infection are appropriate choices. Several single agents are recommended for incisional SSIs involving the intestinal or genital tract, e.g. cefoxitin, ampicillin–sulbactam, piperacillin–tazobactam and imipenem–cilastatin (Table 1) [14]. Recommended combination regimens include fluoroquinolones, third-generation cephalosporins, and aminoglycosides in conjunction with clindamycin, metronidazole or a b-lactam–b-lactamase inhibitor combination [14]. For non-intestinal sites of operation (excluding the axilla or the perineum), oxacillin or a first-generation cephalosporin is recommended (Table 2) [14]. These agents provide coverage against the expected pathogens, e.g. S. aureus (other than MRSA) and streptococcal species. Clindamycin is an acceptable alternative for patients with a history of b-lactam hypersensitivity; however, there is a high potential of cross-resistance and emergence of resistance in erythromycin-resistant strains and of inducible resistance in MRSA [10]. Where the rate of infection with MRSA is high, vancomycin, Table 1. Antibiotic choices for incisional surgical site infections: intestinal or genital tract site of operation Single agents

Combination agents

Cefoxitin

Facultative and aerobic activity Fluoroquinolone Third-generation cephalosporin Aztreonam Aminoglycoside Anaerobic activity Clindamycin Metronidazolea Chloramphenicol Penicillin agent plus b-lactamase inhibitor

Ceftizoxime Ampicillin–sulbactam Ticarcillin–clavulanate Piperacillin–tazobactam Imipenem–cilastatin Meropenem Ertapenem

a Do not combine aztreonam with metronidazole, because this combination has no activity against Gram-positive cocci. Adapted from Ref. [14].

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Table 2. Antibiotic choices for incisional surgical site infections: non-intestinal site of operation

Table 3. Treatment of necrotizing infections of skin, fascia, and musclea

Trunk and extremities away from axilla or perineum Oxacillin First-generation cephalosporin Axilla or perineum Cefoxitin Ampicillin–sulbactam Other single agents as described for intestinal and genital operations (see Table 1)

First-line antimicrobial agent, by infection type

Adapted from Ref. [14].

daptomycin or linezolid are currently recommended, pending results of culture and susceptibility tests. However, the appearance of vancomycin-, linezolid- and daptomycin-resistant strains suggests that new options are needed [17–24]. For infections involving the axilla or the perineum, cefoxitin and ampicillin–sulbactam are the agents of choice [14]. Other monotherapies, as recommended above for intestinal and genital tract sites of operation, may also be used. Treatment of necrotizing infections of the skin, fascia and muscle require broad-spectrum antimicrobials (e.g. piperacillin–sulbactam, ciprofloxacin, or meropenem plus clindamycin or metronidazole) (Table 3) [14]. Appropriate agents for patients with severe penicillin hypersensitivity include clindamycin or metronidazole with an aminoglycoside or fluoroquinolone. The IDSA recommendations also provide pathogen-directed regimens for the treatment of necrotizing cSSTIs (Table 4) [14]. INTRA-ABDOMINAL INFECTIONS Intra-abdominal infections are among the most common infections in general surgery and are frequently severe medical conditions, involving significant morbidity and mortality and carrying a burden of resource use [4]. In a retrospective study of 604 consecutive patients who underwent emergency surgery for unequivocal intra-abdominal infections, a morbidity rate of 59% and a mortality rate of 21% were reported [25]. These data support the idea that optimal management must include early diagnosis, appropriate surgical intervention, and adequate antimicrobial therapy [4]. The consequences of delayed or inappropriate antimicrobial treatment can be severe, leading to an increased risk of death, necessity of re-operation, or prolonged hospitalization.

Mixed infection Ampicillin–sulbactam or Piperacillin–tazobactam plus Clindamycin plus Ciprofloxacin Imipenem–cilastatin Meropenem Ertapenem Cefotaxime plus Metronidazole or Clindamycin

Adult dosage

1.5–3 ⁄ 0 g every 6–8 h IV 3.375 g every 6–8 h IV 600–900 mg ⁄ kg every 8 h IV 400 mg every 12 h IV 1 g every 6–8 h IV 1 g every 8 h IV 1 g every 24 h IV 2 g every 6 h IV 500 mg every 6 h IV 600–900 mg ⁄ kg every 8 h IV

a

If Staphylococcus infection is present or suspected, add an appropriate agent. Adapted from Ref. [14].

Although early adequate surgery or drainage remain the cornerstones of management of intra-abdominal infections and impact on patient outcome, the early administration of adequate empirical broad-spectrum antimicrobial therapy further influences the rates of patient morbidity and mortality. A prospective cohort study of 2000 subjects established a statistically significant relationship between inadequate antimicrobial treatment of infections and hospital mortality in patients requiring intensive-care unit admission [26]. Specifically, 25.8% (169 of 655) of patients assessed as having either community-acquired or nosocomial infections were judged to have received inappropriate empirical therapy. Inadequate antimicrobial treatment of infection was reported most often among patients with nosocomial infections that developed after treatment of a community-acquired infection (45.2%), followed by patients with nosocomial infections alone (34.3%) and patients with community-acquired infections alone (17.1%) (p <0.001). The infectionrelated mortality rate in patients with proven infection who were receiving inadequate antimicrobial therapy (42.0%) was significantly greater than the infection-related mortality rate in infected patients who were receiving adequate antimicrobial therapy (17.7%) (p <0.001). A history of prior antimicrobial therapy was an important risk factor for the administration of inadequate antimicrobials in this patient cohort. Another study, among 425 patients requiring surgery for community-acquired secondary peritonitis, reported that 13% of the patients had received inappropriate initial empirical antibiotic

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Table 4. Pathogen-directed treatment of necrotizing infections of skin, fascia and muscle First-line antimicrobial agent, by infection type Streptococcus infection Penicillin plus Clindamycin Staphylococcus aureus infection Nafcillin Oxacillin Cefazolin Vancomycin Clindamycina Clostridium infection Clindamycin Penicillin

Agents for patients with severe penicillin hypersensitivity

Adult dosage

2–4 MU q 4–6 h IV (adults)

Vancomycin, linezolid, daptomycin or quinupristin–dalfopristin

600–900 mg ⁄ kg every 8 h IV 1–2 g every 4 h IV

Vancomycin, linezolid, daptomycin or quinupristin–dalfopristin

1–2 g every 4 h IV 1 g every 8 h IV 30 mg ⁄ kg ⁄ day in two divided doses IV 600–900 mg ⁄ kg every 8 h IV 600–900 mg ⁄ kg every 8 h IV 2–4 MU every 4–6 h IV

a

Clindamycin is bacteriostatic; potential for cross-resistance and emergence of resistance in erythromycin-resistant strains; inducible resistance in methicillin-resistant S. aureus. Adapted from Ref. [14].

therapy [27]. The same study also confirmed that patients were more likely to have clinical success if initial antibiotic therapy was appropriate (78.6%) than if inappropriate regimens were used (53.4%) [27]. Not surprisingly, this study also found that administration of appropriate antimicrobial therapy, coupled with clinical success, was linked with a 6-day shorter length of hospital stay. A third retrospective study by Bare et al., conducted in northeast Spain in patients with community-acquired intra-abdominal infections, reported that 14% of patients received inappropriate initial empirical antibiotic therapy [28]. They also confirmed the findings of others that inappropriate antibiotic therapy led to less favourable clinical outcomes. Choosing appropriate empirical antimicrobial therapy requires an appreciation of the microbiology of cIAIs. The aetiology of peritonitis depends on whether the infection is primary (also known as spontaneous peritonitis), secondary, or tertiary. Primary peritonitis is less common and usually occurs in the presence of ascites without an evident source of infection. However, when infection occurs, it is typically due to a single organism, e.g. E. coli, Klebsiella spp., Streptococcus spp., or Enterococcus spp. [29,30]. Secondary peritonitis occurs when the peritoneal space is contaminated by endogenous microflora secondary to loss of integrity of the gastrointestinal tract. In most clinical settings, two to three aerobic species and one to two anaerobic species are identified in patients with secondary peritonitis. As such, these polymicrobial infections typically include the aforementioned organisms, along with B. fragilis and Pseudomonas spp., depending on the level of

gastrointestinal disruption [29,30]. Tertiary peritonitis, which is typically caused by multiple pathogens, may include all of the previously mentioned organisms in addition to Staphylococcus epidermidis and Candida sp. [29]. Not unexpectedly, community-acquired peritoneal infections often differ substantially in the microbial causes of infection from those acquired in the nosocomial setting. E. coli and streptococci tend to be isolated more commonly in patients with community-acquired peritonitis, whereas Enterococcus spp., Enterobacter spp., S. aureus and coagulase-negative staphylococci are more common in patients with nosocomial peritonitis [31]. The microbiology of SSIs was evaluated in a 2-year prospective study of 2552 patients who underwent either elective (58%) or emergency (42%) surgery. In total, 19.6% (n = 501) of the patients developed postoperative infections, of which 61.3% had a confirmed aetiology. Among these patients, 84 of 501 had intra-abdominal infections. Gram-negative bacteria were isolated more often (56%) than Gram-positive bacteria (29%), followed by anaerobic flora (13%). This surveillance study found that the most commonly isolated organisms (n = 78) in patients with cIAI were E. coli (32.5%), Enterococcus (15.7%) and Enterobacter cloacae (7.2%) [32]. The guidelines from the IDSA, the Surgical Infection Society, the American Society for Microbiology and the Society of Infectious Disease Pharmacists contain evidence-based recommendations for selection of antimicrobial therapy for adult patients with cIAIs [4,13,33]. In general, intra-abdominal infections may be managed with a variety of single-agent regimens (e.g.

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ampicillin–sulbactam, ertapenem, imipenem– cilastatin, meropenem) and multiple-agent regimens (e.g. cefuroxime ⁄ third- or fourth-generation cephalosporin or ciprofloxacin plus metronidazole), depending on the type of infection (community-acquired or nosocomial) and the severity of the infection (mild ⁄ moderate or severe) [4,13,33]. According to available data, no antimicrobial regimen has been consistently demonstrated to be superior or inferior [4]. However, monotherapy with broad-spectrum antimicrobials has certain advantages, including a reduction in the potential for toxicity or drug interactions [34,35], as well as ease of administration [36]. Specific recommendations put forth in the recent treatment guidelines [4,13,33], although based on the best available evidence, must be individualized according to local resistance data and patient-specific factors. Importantly, most of the recommended antimicrobial regimens have been tested in prospective randomized controlled trials in patients with community-acquired cIAIs. For patients with mildly to moderately severe community-acquired infections, antimicrobials that have a narrower spectrum of activity, e.g. ampicillin–sulbactam, cefazolin or cefuroxime plus metronidazole, ticarcillin–clavulanate, ertapenem and fluoroquinolones plus metronidazole, are considered to be reasonable options (Table 5) [4,13,33]. These agents are favoured because they are more cost-effective and are often less toxic than more potent, broad-spectrum agents, which should be reserved for more serious infections. Most patients with less severe community-acquired infections will experience full recovery following adequate source control and appropriate antimicrobial therapy. Because higher-risk patients with cIAIs (e.g. those with higher APACHE II scores, equal to or greater than 15, poor nutritional status, significant cardiovascular disease, in a situation where adequate source control cannot be provided) are more likely to fail therapy because of resistant organisms, antimicrobial regimens with broader coverage of Gram-negative aerobic ⁄ facultatively anaerobic organisms are recommended. Agents used to treat nosocomial postoperative infections must also provide coverage against P. aeruginosa, Enterobacter spp., Proteus spp., MRSA, enterococci, and Candida spp. Antimicrobial regimens with expanded spectra include

meropenem, imipenem–cilastatin, piperacillin–tazobactam, once-daily aminoglycoside or aztreonam, ciprofloxacin plus clindamycin or metronidazole, and a third- or fourth-generation cephalosporin plus clindamycin or metronidazole (Table 5) [4,13,33]. If P. aeruginosa is a known or likely causative organism, higher doses of some agents may be required to ensure adequate coverage. Additional coverage, e.g. by vancomycin, may be needed if there is a high suspicion of MRSA. However, the appearance of vancomycin-resistant S. aureus escalates the need for new first-line therapies that are effective against MRSA [17]. Although routine coverage for enterococci is discouraged for most patients with cIAIs, it seems prudent for patients with serious nosocomial infections, despite the fact that there are few data showing that such coverage improves outcome [13]. Well-designed studies are needed to compare conventional and newer antimicrobials in patients with nosocomially acquired cIAIs, as few studies have evaluated the differences in clinical outcome in higher-risk patients. Overall, the choice of antimicrobial therapy for patients with nosocomial surgical infections must take into consideration the resistance patterns of likely pathogens, the patient’s history of prior antimicrobial exposure, and the results of the Gram stain of infected peritoneal fluid, whenever possible. ORGANISM-SPECIFIC RESISTANCE AND CSSTIS AND CIAIS The increasing prevalence of resistant pathogens in healthcare settings raises challenges for the treatment of patients with complicated, surgeryrelated infections. Several pathogens of concern include MRSA, which has emerged as the leading cause of postoperative infection, especially in patients with cSSTIs, ESBL-producing Gram-negative bacteria, including CTX-M-type-producing strains, and multidrug-resistant strains of B. fragilis. Community-associated MRSA is also a pending cause of concern in patients with SSIs. Infection with each of these organisms is associated with a higher risk of negative outcome, postoperative consequences, increased length of hospital stay, and increased utilization of hospital resources. The development of new classes of antibiotics that are effective against these problem pathogens is needed.

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Third ⁄ fourth-generation cephalosporin + anti-anaerobic agent Aminoglycoside or ciprofloxacin or aztreonam + anti-anaerobic agent

Imipenem Meropenem

Piperacillin–tazobactam

a When using aztreonam, the addition of an agent with Gram-positive coverage is advised. Adapted from Refs [4,13,33].

Fluoroquinolone + metronidazole

Third ⁄ fourth-generation cephalosporin or aztreonama + metronidazole Ciprofloxacin + metronidazole Cefazolin or cefuroxime + metronidazole Combination therapy

Imipenem Meropenem Ertapenem

Ampicillin–sulbactam Ticarcillin–clavulanate Piperacillin–tazobactam Cefotetan Cefoxitin Ertapenem Imipenem Meropenem Third ⁄ fourth-generation cephalosporin or cefuroxime or aztreonama + anti-anaerobic agent Aminoglycoside + anti-anaerobic agent Piperacillin–tazobactam Ampicillin–sulbactam Ticarcillin–clavulanate Monotherapy

cIAI Mild-to-moderate cIAI

Severe cIAI

Surgical Infection Society Recommendations Infectious Diseases Society of America Recommendations

Table 5. Antimicrobial options for the treatment of complicated intra-abdominal infections (cIAIs)

Higher-risk patient

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A retrospective cohort analysis found that methicillin resistance was independently associated with increased mortality and hospital charges among patients with S. aureus SSIs [37]. This analysis included 193 uninfected control subjects, 121 patients with SSIs due to MRSA, and 165 patients with methicillin-susceptible S. aureus (MSSA) infections. Patients infected with MRSA had a three-fold greater 90-day mortality rate (20.7%) than did patients infected with MSSA (6.7%; p <0.001). Infection with MRSA was also associated with a greater duration of hospitalization after infection (median additional days, 5; p <0.001). MRSA-associated infections also led to higher healthcare expenses. Median hospital charges were $92 363 for patients with MRSA vs. $52 791 for patients with MSSA (p <0.001). Furthermore, there were 1.19-fold increases in hospital charges for patients with MRSA SSIs (p 0.03) and mean attributable excess charges of $13 901 per SSI as compared with patients infected with MSSA. The adverse clinical and economic outcomes associated with MRSA SSIs can be linked, in part, to the availability of only suboptimal antimicrobial agents for this pathogen. Lautermann et al., in a retrospective cohort study, evaluated the effect of ESBL-producing E. coli and K. pneumoniae infection on clinical outcomes [8]. Among the 33 cases that met the criteria for infection, 25 (75.8%) had infections due to K. pneumoniae and eight (24.2%) had infections due to E. coli. Infection with ESBLproducing E. coli or K. pneumoniae was significantly associated with a greater median hospital charge accrued subsequent to infection ($66 590) than was infection with non-ESBL-producing E. coli or K. pneumoniae ($22 231; p 0.04). Kang et al. found that bacteraemia due to ESBL-producing K. pneumoniae (n = 66) was associated with a higher rate of treatment failure at 72 h after the initiation of treatment (35%) as compared with control subjects (15%; p 0.011) [38]. Moreover, the outcome of cephalosporin treatment for bloodstream infections due to ESBLproducing K. pneumoniae was poor, even in the case of apparently susceptible organisms. Overall, these data demonstrate that infections with ESBLproducing E. coli and K. pneumoniae have a significant impact on clinical outcome. Sensible use of all antibiotics, as well as barrier precautions, are important for their effective eradication and to reduce spread.

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Recent data indicate that infections caused by ESBL-producing organisms are an emerging problem in outpatient settings in various parts of the world [39]. CTX-M-type-producing strains have recently gained importance, especially among Enterobacteriaceae. Surveys show that ESBL-producing E. coli, including those producing CTX-M types, exhibit co-resistance to trimethoprim–sulphamethoxazole, tetracycline, gentamicin, and ciprofloxacin [40]. The appearance of these strains in the community may threaten patient care if they are introduced into the hospital. To date, few outbreaks have been identified in the hospital settings; most have been limited to urinary tract infections. Nevertheless, hospital laboratories may need to routinely screen for ESBL-producing Enterobacteriaceae originating from the community so that appropriate therapy can be prescribed and the spread of resistance minimized. Organisms within the B. fragilis group (now also called intestinal Bacteroidales) are the most frequently isolated anaerobic pathogens recovered from blood and abscesses. Among patients with anaerobic and mixed infections, they are also among the most antibiotic-resistant isolates, according to a US national survey (1997–2004) [41]. That study of Bacteroidales spp. examined the trends of susceptibility to various antibiotics in 5225 clinical isolates. Notably, isolates of B. fragilis were those most commonly tested (52%). The rates of resistance to clindamycin and moxifloxacin were high for these isolates, at 19% and 27%, respectively. By contrast, the rates of resistance to carbapenems and b-lactam–b-lactamase inhibitor combinations were low. Remarkably, increases in susceptibility to imipenem, meropenem, piperacillin–tazobactam and cefoxitin (lower MICs) were found for many species within the group, suggesting that these agents are more active now than they were several years ago. The resistance rates for tigecycline, a novel, expanded broadspectrum glycylcycline, were also found to be low and stable (5%) during the surveillance period. For non-B. fragilis spp. (i.e. Bacteroides (now Parabacteroides) distasonis), high MICs of all the b-lactam agents (carbapenems, inhibitor combinations, cefoxitin) and tigecycline were observed. Overall, this surveillance found that the resistance of B. fragilis, Bacteroides ovatus and Bacteroides thetaiotaomicron to clindamycin increased significantly. Metronidazole and chloramphenicol were

the most potent agents tested; only one metronidazole-resistant B. fragilis strain (MIC, 64 mg ⁄ L), the first such strain in the USA, was documented in this study. The emergence of resistance in B. fragilis group isolates, especially against metronidazole, has important implications in the treatment of surgical infections. As in other cases where potentially multiply resistant pathogens are involved, continued monitoring of susceptibility patterns is important to ensure the desired outcome in the treatment of infections due to Bacteroidales. DURATION OF ANTIMICROBIAL THERAPY FOR INTRA-ABDOMINAL INFECTIONS The duration of antimicrobial therapy for intraabdominal infections implies a difficult clinical decision. In general, there is agreement that shorter treatment courses should be used whenever possible, to prevent collateral antibiotic effects as well as the development of resistant microorganisms. It is currently accepted that, in some conditions, antimicrobial therapy should be limited to 24 h or less [13]: traumatic and iatrogenic perforations operated on within 12 h; gastroduodenal perforations operated on within 24 h; acute or gangrenous appendicitis without perforation; acute or gangrenous cholecystitis without perforation; and transmural bowel perforation from embolic, thrombotic or obstructive vascular occlusion without perforation or established peritonitis or abscess. For patients with cIAI, the recommendations are as follows [4]: in general, antimicrobial therapy should be limited to no more than 5–7 days. Patients with localized infections identified at the time of the initial operation, e.g. localized perforation of the appendix, may be treated with even shorter courses of antimicrobial therapy. Antimicrobial therapy may be discontinued in patients who have defervesced, who have normalizing white blood cell counts, and who have returned to normal gastrointestinal function. Patients with persistent signs of systemic infection after an initial course of antimicrobial therapy should undergo clinical investigations to determine the cause of the signs of persistent infection, and they should not be subjected to prolonged antimicrobial therapy or arbitrary changes in antimicrobial agents. Critically ill patients who have poorly

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Caı´nzos Complicated skin ⁄ soft tissue and intra-abdominal infections 17

controlled infections, e.g. those with tertiary peritonitis, may benefit from more prolonged courses of appropriate antimicrobial therapy. CONCLUSIONS The development of surgical site-associated infections is a serious sequela, as these infections contribute significantly to morbidity and mortality. In particular, cSSTIs and cIAIs are responsible for a significant proportion of disease burden in surgical patients. The diagnosis and management of these infections require a high degree of suspicion, prompt surgical intervention, and adequate antibiotic therapy. Therapy should be targeted at the most likely pathogens and adjusted after culture and susceptibility test results become available. Accordingly, current antibiotic use needs to take into account the increasing resistance in Gram-positive bacteria (e.g. MRSA), Gram-negative ESBL-producing Enterobacteriaceae (e.g. E. coli), and the growing resistance to several antimicrobials in anaerobes. Selection of the optimal antimicrobial regimen must also take into account individual patient factors, drug-specific safety profiles, and cost considerations. Recognition of higher-risk patients (e.g. those with an APACHE II score >15, of advanced age, with a non-appendiceal source of infection, a nosocomial infection or a postoperative infection) is the key to achieving the desired response, as potent broad-spectrum therapy is probably needed. Current treatment guidelines for the management of cSSTIs and cIAIs do not reflect the availability of new antibiotics, or the latest trends in bacterial resistance. Furthermore, today’s resistance trends frequently require the use of multiple agents due to the polymicrobial nature of these infections. The increased resistance of bacteria, particularly of MRSA, ESBL-producing Gram-negative bacteria, and the B. fragilis group, to current antibiotics highlights the growing need for new classes of broad-spectrum agents for empirical therapy to treat these serious complications in the surgical patient with mixed infections. TRANSPARENCY DECLARATION M. Caı´nzos declares no conflict of interest.

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