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Acquisition and spread of Acinetobacter baumannii and Stenotrophomonas maltophilia in intensive care patients
ARTICLE IN PRESS
Int. J. Hyg. Environ. Health 212 (2009) 330–337 www.elsevier.de/ijheh
Acquisition and spread of Acinetobacter baumannii and Stenotrophomonas maltophilia in intensive care patients Martina Barchittaa,b, Rosalba Cipressoa, Loredana Giaquintad, Maria Antonietta Romeod, Carmelo Denarod, Carlo Pennisic, Antonella Agodia,b,c, a
Department of Biomedical Sciences, University of Catania, Via S. Sofia n. 87, 95123 Catania, Italy GISIO, Gruppo Italiano Studio Igiene Ospedaliera, SItI, Italy c LaPoSS, Laboratorio di progettazione, sperimentazione e analisi di politiche pubbliche e servizi alle persone, University of Catania, Italy d Intensive Care Unit, Azienda Ospedaliera Cannizzaro, Catania, Italy b
Received 30 April 2008; received in revised form 30 June 2008; accepted 10 July 2008
Abstract Acinetobacter baumannii and Stenotrophomonas maltophilia are increasingly important pathogens, especially in the intensive care units (ICUs). This study was designed to investigate the clonality, the mode of transmission and the patients’ risk profile for acquisition of A. baumannii and S. maltophilia at the ICU of an Italian Hospital. Patterns of A. baumannii and S. maltophilia acquisition in the ICU during the period of the survey were carriage, colonization and infection. Characterization of A. baumannii was performed by ARDRA and genotyping of both pathogens by PFGE. Our study provided evidence for the occurrence of an outbreak sustained by the two organisms in study involving 27.3% of patients enrolled into the surveillance. The spread of a unique A. baumannii epidemic clone was demonstrated. A major clone of S. maltophilia was responsible for the epidemic spread of S. maltophilia (55.5% of isolates), thus confirming A. baumannii cross-transmission and showing – among few published reports – the clonal spread of S. maltophilia. Outliers analysis suggested colonized patients as the probable epidemic sources. Mechanical ventilation was confirmed as risk factor for infection (OR 8.4; 95%C.I.: 2.6–27.5). A multimodal intervention program was introduced, followed in later months with a drastic restriction of infection and colonization due to A. baumannii and S. maltophilia and subsequently with the successful control of the outbreak. Active surveillance of infection and colonization by high-risk clones, together with implementation of control strategies, including strict hand hygiene, proved to be effective to reduce the epidemic spread of both alert pathogens in our ICU. r 2008 Elsevier GmbH. All rights reserved. Keywords: Hospital hygiene; Infection control; Intensive care; Acinetobacter baumannii; Stenotrophomonas malthophilia
Introduction Corresponding author at: Department of Biomedical Sciences, University of Catania, Via S. Sofia n. 87, 95123 Catania, Italy. Tel.: +39 95 3782076; fax: +39 95 3782158. E-mail address: [email protected] (A. Agodi).
1438-4639/$ - see front matter r 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2008.07.001
Acinetobacter baumannii and Stenotrophomonas maltophilia are increasingly important pathogens, especially in the intensive care units (ICUs), because of their
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predictable transmissibility and potential for causing difficult-to-treat nosocomial infections (NIs). In particular, A. baumannii has been increasingly recognized as emerging causes of healthcare-associated infection, particularly in patients who are hospitalized and critically ill, and is usually multidrug resistant (MDR) (McGowan, 2006; Turton et al., 2007). Recently, highly successful strains of specific genotypes have been associated with outbreaks in several hospitals in Europe (Turton et al., 2007). Conventional laboratory techniques do not reliably distinguish A. baumannii from other species of the A. calcoaceticus–A. baumannii complex (Schreckenberger et al., 2003). The A. calcoaceticus– A. baumannii complex consists of the phenotypically similar but genetically diverse A. calcoaceticus and A. baumannii strains, Acinetobacter genomic species 3, and Acinetobacter genomic species 13TU (Vaneechoutte et al., 1995). Thus, studies that do not use molecular techniques to distinguish A. baumannii from related Acinetobacter species may generate inaccurate data regarding clinical epidemiology and disease outcomes. Stenotrophomonas maltophilia has been considered in the past as an unusual opportunistic pathogen with limited invasiveness but its overall isolation rate has increased and infections are at present difficult to manage since clinical isolates are intrinsically resistant to many broad-spectrum antibiotics (Clark et al., 2003; Meyer et al., 2006; Wang et al., 2004). A better understanding of how these organisms emerge and spread is at present required. Both A. baumannii and S. maltophilia may be associated to colonization rather than infection, thereby obscuring the real significance of pathogen isolation (Abbassi et al., 2008; Rodriguez-Bano et al., 2004). These issues have limited understanding of the epidemiology and clinical relevance of A. baumannii and S. maltophilia infections, and prompted us to investigate the clonality by genotyping, the microbial mode of transmission and the patients’ risk profile for acquisition of A. baumannii and S. maltophilia at the interdisciplinary ICU of an Italian hospital.
Methods Setting and survey methodology The 6-month survey was performed at the 12-bed interdisciplinary ICU of the Azienda Ospedaliera Cannizzaro, a 700-bed acute care hospital in Catania, Italy. The surveillance protocol was described in greater detail elsewhere (Agodi et al., 2007; Suetens et al., 2007). Briefly, during the study period all patients who stayed for X48 h at the ICU were enrolled into the patient based surveillance. Patterns of A. baumannii and S. maltophilia acquisition were as follows: (i) carriage on
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admission, (ii) colonization of sterile sites, and (iii) infections during ICU stay. Standard definitions of carriage, colonization and NI were used (Agodi et al., 2007; Bertrand et al., 2001; Suetens et al., 2007). Briefly, patients with screening cultures testing positives on admission in the absence of, or before isolation of, positive clinical specimens were considered to be carriers. Patients with positive clinical specimens were considered to be colonized in the absence of clinical data confirming infection. When both clinical and screening cultures were positive on the same day, the patient was considered as colonized. We included the following NI sites: pneumonia, bloodstream infections, central venous catheter-related bloodstream infections and urinary tract infections, following the Hospital in Europe Link for Infection Control through Surveillance (HELICS) definitions (Suetens et al., 2007). We only considered the first episode of infection or colonization per microrganism, per site and per patient: e.g. if a patient is colonized in the respiratory tract by A. baumannii and then in the urine, as these are two sites, both included. However, if infection developed after colonization at the same site, only the episode of infection was considered in the analysis. Finally, colonization and infections occurring during ICU stay in carriers upon admission were not considered. Incidence rates of colonization and of infections were calculated both in terms of cumulative incidence and incidence density. The University Board and the Head of the Intensive Care Unit approved the research project.
Bacterial isolates All A. baumannii and S. maltophilia isolates were collected and identified by the Phoenix system (Becton Dickinson Diagnostic System, Pont de Claix, France). The Acinetobacter genomic species was determined by amplified rDNA restriction analysis (ARDRA) (Dijkshoorn et al., 1998; Vaneechoutte et al., 1995). Briefly, the amplified 16S rRNA gene was obtained by PCR, and then separate aliquots were digested with five restriction endonucleases (CfoI, AluI, MboI, RsaI, and MspI). The fragments obtained by digestion with each enzyme were electrophoretically separated in 3.0% agarose gels. Species identification was achieved by comparing the profiles consisting of the combination of restriction patterns to those of a library of strains of described species (Dijkshoorn et al., 1998; Vaneechoutte et al., 1995; http://allserv.rug.ac.be/_mvaneech/ARDRA/ Acinetobacter.html). Antibiotic susceptibility was determined using an automated Phoenix microdilution system (Becton Dickinson Diagnostic System, Pont de Claix, France). Multi-drug resistance (MDR) was defined as resistance of an isolate to at least three different classes of antimicrobials, including
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cephalosporins, penicillins, b-lactams and b-lactamase inhibitor combinations, monobactams, fluoroquinolones and aminoglycosides.
Macrorestriction analysis and identification of cross-transmission episodes Molecular typing by pulsed-field gel electrophoresis (PFGE) of the digested genomic DNA was performed using different protocols for each bacterial species as previously described (Agodi et al., 2006; Denton et al., 1998). Briefly, genomic DNA was digested with 30 U/ml of ApaI for A. baumannii and 25 U/ml of XbaI for S. maltophilia. Macrorestriction fragments were separated using a CHEF-DR III apparatus (Bio-Rad Laboratories, Hercules, CA). Interpretation of genomic relatedness was performed using well-established criteria (Tenover et al., 1995). A cross-transmission episode was assumed when two patients had indistinguishable isolates (Weist et al., 2002) and were treated in the ICU during intervals that overlapped or were no more than 7 days apart (Halwani et al., 2006).
patients were all those without NI. Furthermore, a casecontrol study was designed for patients with or without infection sustained by at least one of the two microrganisms in study: case patients were all those with NI diagnosis, while control patients were all those without NI. The patients’ characteristics and variables examined as possible risk factors were sex, SAPS II score, dead in the ICU, exposure to surgical procedures prior to ICU admission, diabetes, chronic renal insufficiency, chronic pulmonary disease and neoplastic disease. For variables that were clearly dependent on the length of stay (number of days of having nasogastric tube, central venous catheter, urinary catheter, and mechanical ventilation), the proportion of the stay with the exposure of interest was used to categorize patients in those not exposed or exposed for part of their stay and those exposed for the whole length of stay (Halwani et al., 2006). Furthermore, the level of nurse-to-patient staffing ratios was computed by dividing the total number of nurses working during a given day by the patient census for that day (Hugonnet et al., 2007).
Statistical analysis Outbreak investigation Since an outbreak was suspected, for each microrganism, the specific epidemic curve was plotted to give a visual representation of the trend of infection events over the time period. Particularly, the epidemic curve was used to provide information on the outbreak pattern of spread, magnitude, time trend and outliers. Outlier analysis, which is the study of cases that stand apart from the overall epidemic curve pattern, and which led to identification of potential sources for the three outbreaks, was also performed (CDC, 1992).
Statistical analyses were performed using SPSS 14.0 statistical package. Resistance rates, colonization rates and infection rates are presented as percentages. Rates were compared using Chi-square test. The significance level was set at an alpha of 0.05. Variables for which the p-value was o0.05 in univariate analysis were included in a logistic regression model for multivariate analysis. A backward stepwise process was used and odds ratios (OR) and 95% confidence intervals (CI) were calculated.
Environmental screening
Results
Since the outbreak continued, environmental sampling was taken including swabs from the patient’s direct environment including equipment. Samples were taken using cotton-tipped swabs moistened with sterile saline. Swabs and rinsing fluid were cultured on antibiotic-supplemented and standard MacConkey agar plates and incubated aerobically at 35 1C for up to 48 h.
Epidemiological patterns of A. baumannii and S. maltophilia acquisition
Case-control study design In order to identify the individual risk factors for acquiring an infection a case-control study was designed for patients with or without infection sustained by each of the two microrganisms in study, separately: case patients were all those with NI diagnosis, while control
During the study period, 121 consecutive patients were enrolled in the study. A total of 47 A. baumannii isolates were identified from 21 patients (17.3%, 21 over 121 patients) and a total of 45 S. maltophilia isolates from 21 patients (17.3%, 21 over 121 patients). A total of 9 patients were colonized and/or infected by both pathogens. A total of 31 colonization episodes were identified in 25 different patients and 31 infections were identified in 22 different patients with at least one of the emerging pathogens in study. Total and pathogenspecific ICU-acquired colonization and infection rates are reported in Table 1.
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Table 1.
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Epidemiological patterns of A. baumannii and S. maltophilia acquisition A. baumannii
S. maltophilia
Total
Number of isolates Carriage at admission (/100 patients) ICU-acquired colonization (/100 patients) Incidence density of colonization (/1000 patient-days) ICU-acquired infection (/100 patients) Incidence density of infection (/1000 patient-days)
47 0 14.9 8.3 13.2 7.4
45 0 10.7 6.0 12.4 6.9
92 0 25.6 14.3 25.6 14.3
Genotyping
Table 2.
Microrganism
Number of crosstransmission episodes of infection and colonization (number of infections and colonizations)
Impact of crosstransmission of infection and colonization (%)
A. baumannii S. maltophilia
18 (34) 17 (28)
52.9 60.7
Total
35 (62)
56.4
10
S. maltophilia
8 7 6 5 4 3 2 1 0
Antimicrobial resistance
A. baumannii
9
Number of infections
All A. baumannii isolates identified by the Phoenix system had the combined ARDRA profile for the respective enzymes CfoI, AluI, MboI, RsaI and MspI, which, according to the library of profiles of reference strains, confirmed at the molecular level the organisms as A. baumannii. A total of 60 strains, 33 A. baumannii and 27 S. maltophilia isolates, were subjected to macrorestriction analysis. A single PFGE-type with four distinct subtypes was shown among the A. baumannii isolates, thus the spread of a unique epidemic clone was demonstrated. Four distinct clones were identified among the S. maltophilia isolates, all associated with crosstransmission of infection and/or colonization; a major clone (named clone A) was responsible for the epidemic spread of S. maltophilia (55.5% of isolates), followed by clone D (25.9%), clone B (11.1%) and clone C (7.5%). Clone A was significantly associated to infection (90.9% of events) rather than to colonization (9.1% events) po0.05. The impact of cross-transmission due to A. baumannii and S. maltophilia infection was estimated to be at least 64.5% of all infections. When cross-transmission of colonization was included the impact of cross-transmission was at least 56.4% (Table 2).
Cross-transmissions by microorganism
Jan
Feb
Mar
Apr
May
Jun
July
Months
All A. baumannii and S. maltophilia isolates were MDR. Particularly, all A. baumannii isolates were sensitive to carbapenems and 97.8% of S. maltophilia isolates were resistant to ciprofloxacin. In particular, S. maltophilia clone A (15 isolates) displayed high resistance to fluoroquinolones, that is 100% to ciprofloxacin and 66.7% to levofloxacin, but was 100% sensitive to trimethoprim/sulphamethoxazole.
Epidemic curves and outbreak investigation The specific epidemic curves were constructed to plot the occurrence of both microrganism-associated
Fig. 1. Number of infections by microrganism over the time period.
infection and colonization events (Fig. 1 and data not shown, respectively). The curves suggest the occurrence of an outbreak sustained by the two pathogens involving a total of 33 patients (27.3% of all enrolled patients). The shape of each curve, containing two peaks, suggests a propagated or progressive-source mode of epidemic transmission, reflective of the number of cases caused by person-to-person contact. The outlier analysis led to the identification of potential sources of the two pathogens: a burn patient,
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from a different hospital, colonized on ICU admission by S. maltophilia clone C and a patient who became colonized by A. baumannii during ICU stay. All environmental cultures were taken at midoutbreak period and resulted negative for A. baumannii and S. maltophilia. When the outbreak was identified, at the beginning of March, a multimodal infection control program was introduced in order to control the acquisition and spread of A. baumannii and S. maltophilia in the ICU, including review of all healthcare procedures, training of staff in the correct washing of hands, introduction of alcohol-based antiseptic gel, enhanced cleaning and disinfection of medical equipment and wards and use of single-patient medical instruments. In the 4 months following the implementation of the above-described measures, a decrease in the incidence of recovery of new A. baumannii and S. maltophilia isolates from patients was observed, and subsequently no new cases of A. baumannii and S. maltophilia were reported in our unit.
to length of mechanical ventilation (Table 3). Multivariate logistic regression analysis was used to adjust for possible confounding effects. Mechanical ventilation for the entire length of stay against exposure for part of patient stay remained statistically significant in the final models for A. baumannii (OR 8.1; 95%C.I.: 1.7–38.8) and for S. maltophilia (OR 9.9; 95%C.I.: 2.0–48.2) infections. Univariate analysis showed that infection due to at least one microrganism was significantly associated with length of mechanical ventilation and with surgical procedure (Table 3). Mechanical ventilation for the entire length of stay (OR 8.4; 95%C.I.: 2.6–27.5) and exposure to surgical procedures prior to ICU admission (OR 4.8; 95%C.I.: 1.0–23.4) remained statistically significant in the final model of multivariate analysis. Furthermore, the 24-h nurse-to-patient ratio resulted greater than 1 during the entire period of the survey (median 1.3, range 1.2–1.6). Thus, no association between the nurse-to-patient ratio and the outbreak was shown in our study.
Risk factor analysis
Discussion
Univariate analysis showed that A. baumannii infection was significantly related to chronic renal insufficiency and to the length of mechanical ventilation. S. maltophilia infection was significantly related to surgical procedure, to chronic renal insufficiency and
The aim of our study was to investigate the genotyping of A. baumannii and S. maltophilia, their genetic relatedness and epidemiological links, their mode of transmission and the patients’ risk profile for their acquisition at the ICU of an Italian Hospital.
Table 3.
Risk factors for infection by univariate analysis
Variables
A. baumannii
Dead in the ICU Mechanical ventilation (entire length of stay) Central venous catheter (entire length of stay) Nasogastric tube (entire length of stay) Urinary Catheter (entire length of stay) Surgical procedures (Yes) Diabetes (Yes) Chronic renal insufficiency (Yes) Chronic pulmonary disease (Yes) Neoplastic disease (Yes)
S. maltophilia
At least one microorganism
Case patients (%) (N ¼ 13)
Control patients (%) (N ¼ 108)
pValue
Case patients (%) (N ¼ 13)
Control patients (%) (N ¼ 108)
pValue
Case patients (%) (N ¼ 22)
Control patients (%) (N ¼ 99)
pValue
50.0 83.3
23.8 38.1
0.800 0.004
38.5 84.6
25.0 37.5
0.325 0.002
42.9 81.0
22.9 34.4
0.098 0.000
75.0
81.9
0.695
69.2
82.7
0.263
66.7
84.4
0.071
91.7
97.1
0.360
84.6
98.0
0.062
85.7
98.9
0.119
91.7
88.6
1.000
84.6
89.4
0.637
85.7
89.6
0.701
84.6
70.4
0.348
68.5
0.019
90.9
67.7
0.035
38.5 31.5
16.3 10.5
0.068 0.016
38.5 46.2
16.3 14.3
0.068 0.012
31.8 18.2
15.8 11.5
0.126 0.476
8.3
16.3
0.688
9.1
16.2
1.000
5.3
17.5
0.299
7.7
13.1
1.000
15.4
12.1
0.666
13.6
12.2
1.000
1.000
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Our study provided evidence for the occurrence of an outbreak sustained by A. baumannii and S. maltophilia involving 27.3% of patients enrolled into the surveillance. The epidemic spread of A. baumannii confirmed the role of cross-transmission as a common mechanism of acquisition of such nosocomial pathogen also in our geographic area (Agodi et al., 2006; Zarrilli et al., 2007). Conversely, cross-infection with S. maltophilia is not common, and only a few clones have been associated to transmission among different patients, producing outbreaks and epidemics (Abbassi et al., 2008; Crispino et al., 2002; Gu¨lmez and Hasc¸elik, 2005; Valdezate et al., 2004). Besides, it has been reported that S. maltophilia isolates display high genetic diversity, even when isolated in a single hospital. This is indicative of the polyclonal nature of emergence of these resistant bacteria and may be related to the wide environmental distribution of this pathogen (Tan et al., 2007). Notably, in our ICU we were able to identify a major S. maltophilia clone, accounting at least for 55.5% of all isolates, responsible for the epidemic spread of this microrganism. In general, the estimated proportion of cases resulting from transmission may vary depending on the occurrence of outbreaks in the period of study (Mikolajczyk et al., 2007). In our study the proportion of NIs as a result of cross-transmission of the two pathogens in study accounted for 64.5% of the total number of ICU-acquired infections, the highest figures reported so far by analogous studies (Grundmann et al., 2005; Halwani et al., 2006; Weist et al., 2002). In our study colonization was shown to represent a considerable part of the bacterial load within the ICU, which would not have been discovered without our specifically focused surveillance program (Abbassi et al., 2008; Rodriguez-Bano et al., 2004). Besides, S. maltophilia major clone, was significantly associated to infection rather than to colonization, thus suggesting to bear specific virulence traits that need to be further characterized. However, the fact that two patients share an organism belonging to the same clone does not necessarily mean that a cross-transmission event did occur; acquisition from a common environmental reservoir, which is fairly common with these organisms, may also have occurred. In the absence of evidences of environmental contamination, transient hand carriage by the ICU personnel was suspected to be the mode of transmission. Moreover, analysis of the outbreak outliers led to the identification of a burn patient from a different hospital colonized on ICU admission by S. maltophilia and a patient who became colonized by A. baumannii during ICU stay as the probable epidemic sources. Strain delineation by the means of molecular methods proved essential in establishing the epidemiologic characteristics of infection due to such organisms and in designing
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rational control measures. Thus, colonization was confirmed to represent not only a considerable element of the bacterial load within the ICU but also a continuous potential source of cross-transmission of specific successful clones. Patients colonized at admission can introduce the pathogen into hospital units. If screened at admission, these patients can be detected and isolated, thus reducing the risk of transmission for others. Such active screening of all or just high-risk patients is standard procedure in some settings but not in others. Anyway, wherever cross-transmission is an indicator of poor quality of care, infection control policies should be improved and identification of alert organisms should trigger additional control measures (van Belkum et al., 2007). The early detection of colonized or infected patients and the prompt implementation of infection control measures are significant factors in the control of bacterial spread. Besides, several cohort studies with a before–after design demonstrated a substantial reduction in infection rates by introducing multimodal infection control programs (Gastmeier, 2007). In our unit, a series of measures was taken to implement hygiene norms and ensure compliance with them. Although our study was not intended to investigate the infection control efficacy, our multimodal program, implemented when the outbreak was identified, that is at the beginning of March, was followed in later months with a drastic restriction of infection and colonization due to A. baumannii and S. maltophilia and subsequently with the successful control of the outbreak. Elucidation of the risk factors associated with the acquisition of MDR A. baumannii and S. maltophilia has been related to a large number of variables. Mechanical ventilation is an established risk factor for crosstransmission and it has been suggested that a longer patients’ time exposure increases the chance of infection (Halwani et al., 2006; van der Kooi et al., 2007). In the present study, those patients who were ventilated for the entire length of stay were shown to be at higher risk of infection compared with those at risk for a portion of their length of stay. Regular monitoring of mechanically ventilated patients requires they to be touched repeatedly, thus increasing the risk of cross-transmission when proper hand hygiene is lacking. Exposure to surgical procedures prior to ICU admission was shown to increase nearly five-fold the risk of infection, as already reported elsewhere (Giamberardino et al., 2007; Meric et al., 2005; Ponce de Leo´n-Rosales et al., 2000). In conclusion, the present study described an integrated approach, consisting of active surveillance of infection and colonization by high-risk clones, together with implementation of control strategies, including strict hand hygiene, and the effective control of the epidemic spread of both alert pathogens in the ICU.
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Acknowledgements This work was supported by grants from the University of Catania, Italy (Progetti di Ricerca di Ateneo to A.A.). This study was presented, in part, at the 17th European Congress of Clinical Microbiology and Infectious Diseases, 31 March–3 April 2007, Munich, Germany.
References Abbassi, M.S., Touati, A., Achour, W., Cherif, A., Jabnoun, S., Khrouf, N., Ben Hassen, A., 2008. Stenotrophomonas maltophilia responsible for respiratory infections in neonatal intensive care unit: antibiotic susceptibility and molecular typing. Pathol. Biol. 3. Agodi, A., Zarrilli, R., Barchitta, M., Anzaldi, A., Di Popolo, A., Mattaliano, A., Ghiraldi, E., Travali, S., 2006. Alertsurveillance of ICU-acquired Acinetobacter infections in a Sicilian hospital. Clin. Microbiol. Infect. 12, 241–247. Agodi, A., Barchitta, M., Cipresso, R., Giaquinta, L., Romeo, M.A., Denaro, C., 2007. Pseudomonas aeruginosa carriage, colonization, and infection in ICU patients. Intensive Care Med. 33, 1155–1161. Bertrand, X., Thouverez, M., Talon, D., et al., 2001. Endemicity, molecular diversity and colonisation routes of Pseudomonas aeruginosa in intensive care units. Intensive Care Med. 27, 1263–1268. CDC, 1992. Principles of Epidemiology, second ed. Public Health Practice Program Office, Atlanta, GA. Clark, N.M., Patterson, J., Lynch III, J.P., 2003. Antimicrobial resistance among gram-negative organisms in the intensive care unit. Curr. Opin. Crit. Care 9, 413–423. Crispino, M., Boccia, M.C., Bagattini, M., Villari, P., Triassi, M., Zarrilli, R., 2002. Molecular epidemiology of Stenotrophomonas maltophilia in a university hospital. J. Hosp. Infect. 52, 88–92. Denton, M., Todd, N.J., Kerr, K.G., Hawkey, P.M., Littlewood, J.M., 1998. Molecular epidemiology of Stenotrophomonas maltophilia isolated from clinical specimens from patients with cystic fibrosis and associated environmental samples. J. Clin. Microbiol. 36, 1953–1958. Dijkshoorn, L., van Harsselaar, B., Tjernberg, I., Bouvet, P.J.M., Vaneechoutte, M., 1998. Evaluation of amplified ribosomal DNA restriction analysis for identification of Acinetobacter genomic species. Syst. Appl. Microbiol. 21, 33–39. Gastmeier, P., 2007. Evidence-based infection control in the ICU (except catheters). Curr. Opin. Crit. Care 13, 557–562. Giamberardino, H.I., Cesa´rio, E.P., Carmes, E.R., Mulinari, R.A., 2007. Risk factors for nosocomial infection in trauma patients. Braz. J. Infect. Dis. 11, 285–289. Grundmann, H., Barwolff, S., Tami, A., et al., 2005. How many infections are caused by patient-to-patient transmission in intensive care units? Crit. Care Med. 33, 946–951. Gu¨lmez, D., Hasc¸elik, G., 2005. Stenotrophomonas maltophilia: antimicrobial resistance and molecular typing of an
emerging pathogen in a Turkish university hospital. Clin. Microbiol. Infect. 11, 880–886. Halwani, M., Solaymani-Dodaran, M., Grundmann, H., Coupland, C., Slack, R., 2006. Cross-transmission of nosocomial pathogens in an adult intensive care unit: incidence and risk factors. J. Hosp. Infect. 63, 39–46. Hugonnet, S., Chevrolet, J.C., Pittet, D., 2007. The effect of workload on infection risk in critically ill patients. Crit. Care Med. 35, 76–81. McGowan, J.E., 2006. Resistance in nonfermenting gramnegative bacteria: multidrug resistance to the maximum. Am. J. Infect. Control 34, S29–S37. Meric, M., Willke, A., Caglayan, C., Toker, K., 2005. Intensive care unit-acquired infections: incidence, risk factors and associated mortality in a Turkish university hospital. Jpn. J. Infect. Dis. 58, 297–302. Meyer, E., Schwab, F., Gastmeier, P., Rueden, H., Daschner, F.D., Jonas, D., 2006. Stenotrophomonas maltophilia and antibiotic use in German intensive care units: data from Project SARI. J. Hosp. Infect. 64, 238–243. Mikolajczyk, R.T., Sagel, U., Bornemann, R., Kramer, A., Kretzschmar, M., 2007. A statistical method for estimating the proportion of cases resulting from cross-transmission of multi-resistant pathogens in an intensive care unit. J. Hosp. Infect. 65, 149–155. Ponce de Leo´n-Rosales, S.P., Molinar-Ramos, F., Domı´ nguez-Cherit, G., Rangel-Frausto, M.S., Va´zquez-Ramos, V.G., 2000. Prevalence of infections in intensive care units in Mexico: a multicenter study. Crit. Care Med. 28, 1316–1321. Rodriguez-Bano, J., Cisneros, J.M., Fernandez-Cuenca, F., et al., 2004. Clinical features and epidemiology of Acinetobacter baumannii colonization and infection in Spanish hospitals. Infect. Control Hosp. Epidemiol. 25, 819–824. Schreckenberger, P., Daneshvar, M., Weyant, R.S., Hollis, D., 2003. Acinetobacter, Achromobacter, Chryseobacterium, Moraxella, and other nonfermentative gram-negative rods. In: Murray, P.R., Baron, E.J., Jorgensen, J.H., Pfaller, M.A., Yolken, R.H. (Eds.), Manual of Clinical Microbiology, eighth ed. ASM Press, Washington, DC, pp. 749–779. Suetens, C., Morales, I., Savey, A., et al., 2007. European surveillance of ICU-acquired infections (HELICS-ICU): methods and main results. J. Hosp. Infect. 65, S171–S173. Tan, C.K., Liaw, S.J., Yu, C.J., Teng, L.J., Hsueh, P.R., 2007. Extensively drug-resistant Stenotrophomonas maltophilia in a tertiary care hospital in Taiwan: microbiologic characteristics, clinical features, and outcomes. Diagn. Microbiol. Infect. Dis. 18. Tenover, F.C., Arbeit, R.D., Goering, R.V., et al., 1995. Interpreting chromosomal DNA restriction patterns produced by pulsed field gel electrophoresis: criteria for bacterial strain typing. J. Clin. Microbiol. 33, 2233–2239. Turton, J.F., Gabriel, S.N., Valderrey, C., Kaufmann, M.E., Pitt, T.L., 2007. Use of sequence-based typing and multiplex PCR to identify clonal lineages of outbreak strains of Acinetobacter baumannii. Clin. Microbiol. Infect. 13, 807–815. Valdezate, S., Vindel, A., Martı´ n-Da´vila, P., Sa´nchez Del Saz, B., Vaquero, F., Canto, R., 2004. High genetic diversity among Stenotrophomonas maltophilia strains despite their
ARTICLE IN PRESS M. Barchitta et al. / Int. J. Hyg. Environ. Health 212 (2009) 330–337
originating at a single hospital. J. Clin. Microbiol. 42, 693–699. van Belkum, A., Tassios, P.T., Dijkshoorn, L., et al., 2007. Guidelines for the validation and application of typing methods for use in bacterial epidemiology. Clin. Microbiol. Infect. 13, 1–46. van der Kooi, T.I.I., de Boer, A.S., Mannie¨n, J., et al., 2007. Incidence and risk factors of device-associated infections and associated mortality at the intensive care in the Dutch surveillance system. Intensive Care Med. 33, 271–278. Vaneechoutte, M., Dijkshoorn, L., Tjernberg, I., et al., 1995. Identification of Acinetobacter genomic species by amplified ribosomal DNA restriction analysis. J. Clin. Microbiol. 33, 11–15.
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Wang, W.S., Liu, C.P., Lee, C.M., et al., 2004. Stenotrophomonas maltophilia bacteremia in adults: four years’ experience in a medical center in northern Taiwan. J. Microbiol. Immunol. Infect. 37, 359–365. Weist, K., Pollege, K., Schultz, I., Ruden, H., Gastmeier, P., 2002. How many nosocomial infections are associated with cross-transmission? A prospective cohort study in a surgical intensive care unit. Infect. Control Hosp. Epidemiol. 23, 127–132. Zarrilli, R., Casillo, R., Di Popolo, A., et al., 2007. Molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii in a university hospital in Italy. Clin. Microbiol. Infect. 13, 481–489.
Int. J. Hyg. Environ. Health 212 (2009) 330–337 www.elsevier.de/ijheh
Acquisition and spread of Acinetobacter baumannii and Stenotrophomonas maltophilia in intensive care patients Martina Barchittaa,b, Rosalba Cipressoa, Loredana Giaquintad, Maria Antonietta Romeod, Carmelo Denarod, Carlo Pennisic, Antonella Agodia,b,c, a
Department of Biomedical Sciences, University of Catania, Via S. Sofia n. 87, 95123 Catania, Italy GISIO, Gruppo Italiano Studio Igiene Ospedaliera, SItI, Italy c LaPoSS, Laboratorio di progettazione, sperimentazione e analisi di politiche pubbliche e servizi alle persone, University of Catania, Italy d Intensive Care Unit, Azienda Ospedaliera Cannizzaro, Catania, Italy b
Received 30 April 2008; received in revised form 30 June 2008; accepted 10 July 2008
Abstract Acinetobacter baumannii and Stenotrophomonas maltophilia are increasingly important pathogens, especially in the intensive care units (ICUs). This study was designed to investigate the clonality, the mode of transmission and the patients’ risk profile for acquisition of A. baumannii and S. maltophilia at the ICU of an Italian Hospital. Patterns of A. baumannii and S. maltophilia acquisition in the ICU during the period of the survey were carriage, colonization and infection. Characterization of A. baumannii was performed by ARDRA and genotyping of both pathogens by PFGE. Our study provided evidence for the occurrence of an outbreak sustained by the two organisms in study involving 27.3% of patients enrolled into the surveillance. The spread of a unique A. baumannii epidemic clone was demonstrated. A major clone of S. maltophilia was responsible for the epidemic spread of S. maltophilia (55.5% of isolates), thus confirming A. baumannii cross-transmission and showing – among few published reports – the clonal spread of S. maltophilia. Outliers analysis suggested colonized patients as the probable epidemic sources. Mechanical ventilation was confirmed as risk factor for infection (OR 8.4; 95%C.I.: 2.6–27.5). A multimodal intervention program was introduced, followed in later months with a drastic restriction of infection and colonization due to A. baumannii and S. maltophilia and subsequently with the successful control of the outbreak. Active surveillance of infection and colonization by high-risk clones, together with implementation of control strategies, including strict hand hygiene, proved to be effective to reduce the epidemic spread of both alert pathogens in our ICU. r 2008 Elsevier GmbH. All rights reserved. Keywords: Hospital hygiene; Infection control; Intensive care; Acinetobacter baumannii; Stenotrophomonas malthophilia
Introduction Corresponding author at: Department of Biomedical Sciences, University of Catania, Via S. Sofia n. 87, 95123 Catania, Italy. Tel.: +39 95 3782076; fax: +39 95 3782158. E-mail address: [email protected] (A. Agodi).
1438-4639/$ - see front matter r 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2008.07.001
Acinetobacter baumannii and Stenotrophomonas maltophilia are increasingly important pathogens, especially in the intensive care units (ICUs), because of their
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predictable transmissibility and potential for causing difficult-to-treat nosocomial infections (NIs). In particular, A. baumannii has been increasingly recognized as emerging causes of healthcare-associated infection, particularly in patients who are hospitalized and critically ill, and is usually multidrug resistant (MDR) (McGowan, 2006; Turton et al., 2007). Recently, highly successful strains of specific genotypes have been associated with outbreaks in several hospitals in Europe (Turton et al., 2007). Conventional laboratory techniques do not reliably distinguish A. baumannii from other species of the A. calcoaceticus–A. baumannii complex (Schreckenberger et al., 2003). The A. calcoaceticus– A. baumannii complex consists of the phenotypically similar but genetically diverse A. calcoaceticus and A. baumannii strains, Acinetobacter genomic species 3, and Acinetobacter genomic species 13TU (Vaneechoutte et al., 1995). Thus, studies that do not use molecular techniques to distinguish A. baumannii from related Acinetobacter species may generate inaccurate data regarding clinical epidemiology and disease outcomes. Stenotrophomonas maltophilia has been considered in the past as an unusual opportunistic pathogen with limited invasiveness but its overall isolation rate has increased and infections are at present difficult to manage since clinical isolates are intrinsically resistant to many broad-spectrum antibiotics (Clark et al., 2003; Meyer et al., 2006; Wang et al., 2004). A better understanding of how these organisms emerge and spread is at present required. Both A. baumannii and S. maltophilia may be associated to colonization rather than infection, thereby obscuring the real significance of pathogen isolation (Abbassi et al., 2008; Rodriguez-Bano et al., 2004). These issues have limited understanding of the epidemiology and clinical relevance of A. baumannii and S. maltophilia infections, and prompted us to investigate the clonality by genotyping, the microbial mode of transmission and the patients’ risk profile for acquisition of A. baumannii and S. maltophilia at the interdisciplinary ICU of an Italian hospital.
Methods Setting and survey methodology The 6-month survey was performed at the 12-bed interdisciplinary ICU of the Azienda Ospedaliera Cannizzaro, a 700-bed acute care hospital in Catania, Italy. The surveillance protocol was described in greater detail elsewhere (Agodi et al., 2007; Suetens et al., 2007). Briefly, during the study period all patients who stayed for X48 h at the ICU were enrolled into the patient based surveillance. Patterns of A. baumannii and S. maltophilia acquisition were as follows: (i) carriage on
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admission, (ii) colonization of sterile sites, and (iii) infections during ICU stay. Standard definitions of carriage, colonization and NI were used (Agodi et al., 2007; Bertrand et al., 2001; Suetens et al., 2007). Briefly, patients with screening cultures testing positives on admission in the absence of, or before isolation of, positive clinical specimens were considered to be carriers. Patients with positive clinical specimens were considered to be colonized in the absence of clinical data confirming infection. When both clinical and screening cultures were positive on the same day, the patient was considered as colonized. We included the following NI sites: pneumonia, bloodstream infections, central venous catheter-related bloodstream infections and urinary tract infections, following the Hospital in Europe Link for Infection Control through Surveillance (HELICS) definitions (Suetens et al., 2007). We only considered the first episode of infection or colonization per microrganism, per site and per patient: e.g. if a patient is colonized in the respiratory tract by A. baumannii and then in the urine, as these are two sites, both included. However, if infection developed after colonization at the same site, only the episode of infection was considered in the analysis. Finally, colonization and infections occurring during ICU stay in carriers upon admission were not considered. Incidence rates of colonization and of infections were calculated both in terms of cumulative incidence and incidence density. The University Board and the Head of the Intensive Care Unit approved the research project.
Bacterial isolates All A. baumannii and S. maltophilia isolates were collected and identified by the Phoenix system (Becton Dickinson Diagnostic System, Pont de Claix, France). The Acinetobacter genomic species was determined by amplified rDNA restriction analysis (ARDRA) (Dijkshoorn et al., 1998; Vaneechoutte et al., 1995). Briefly, the amplified 16S rRNA gene was obtained by PCR, and then separate aliquots were digested with five restriction endonucleases (CfoI, AluI, MboI, RsaI, and MspI). The fragments obtained by digestion with each enzyme were electrophoretically separated in 3.0% agarose gels. Species identification was achieved by comparing the profiles consisting of the combination of restriction patterns to those of a library of strains of described species (Dijkshoorn et al., 1998; Vaneechoutte et al., 1995; http://allserv.rug.ac.be/_mvaneech/ARDRA/ Acinetobacter.html). Antibiotic susceptibility was determined using an automated Phoenix microdilution system (Becton Dickinson Diagnostic System, Pont de Claix, France). Multi-drug resistance (MDR) was defined as resistance of an isolate to at least three different classes of antimicrobials, including
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cephalosporins, penicillins, b-lactams and b-lactamase inhibitor combinations, monobactams, fluoroquinolones and aminoglycosides.
Macrorestriction analysis and identification of cross-transmission episodes Molecular typing by pulsed-field gel electrophoresis (PFGE) of the digested genomic DNA was performed using different protocols for each bacterial species as previously described (Agodi et al., 2006; Denton et al., 1998). Briefly, genomic DNA was digested with 30 U/ml of ApaI for A. baumannii and 25 U/ml of XbaI for S. maltophilia. Macrorestriction fragments were separated using a CHEF-DR III apparatus (Bio-Rad Laboratories, Hercules, CA). Interpretation of genomic relatedness was performed using well-established criteria (Tenover et al., 1995). A cross-transmission episode was assumed when two patients had indistinguishable isolates (Weist et al., 2002) and were treated in the ICU during intervals that overlapped or were no more than 7 days apart (Halwani et al., 2006).
patients were all those without NI. Furthermore, a casecontrol study was designed for patients with or without infection sustained by at least one of the two microrganisms in study: case patients were all those with NI diagnosis, while control patients were all those without NI. The patients’ characteristics and variables examined as possible risk factors were sex, SAPS II score, dead in the ICU, exposure to surgical procedures prior to ICU admission, diabetes, chronic renal insufficiency, chronic pulmonary disease and neoplastic disease. For variables that were clearly dependent on the length of stay (number of days of having nasogastric tube, central venous catheter, urinary catheter, and mechanical ventilation), the proportion of the stay with the exposure of interest was used to categorize patients in those not exposed or exposed for part of their stay and those exposed for the whole length of stay (Halwani et al., 2006). Furthermore, the level of nurse-to-patient staffing ratios was computed by dividing the total number of nurses working during a given day by the patient census for that day (Hugonnet et al., 2007).
Statistical analysis Outbreak investigation Since an outbreak was suspected, for each microrganism, the specific epidemic curve was plotted to give a visual representation of the trend of infection events over the time period. Particularly, the epidemic curve was used to provide information on the outbreak pattern of spread, magnitude, time trend and outliers. Outlier analysis, which is the study of cases that stand apart from the overall epidemic curve pattern, and which led to identification of potential sources for the three outbreaks, was also performed (CDC, 1992).
Statistical analyses were performed using SPSS 14.0 statistical package. Resistance rates, colonization rates and infection rates are presented as percentages. Rates were compared using Chi-square test. The significance level was set at an alpha of 0.05. Variables for which the p-value was o0.05 in univariate analysis were included in a logistic regression model for multivariate analysis. A backward stepwise process was used and odds ratios (OR) and 95% confidence intervals (CI) were calculated.
Environmental screening
Results
Since the outbreak continued, environmental sampling was taken including swabs from the patient’s direct environment including equipment. Samples were taken using cotton-tipped swabs moistened with sterile saline. Swabs and rinsing fluid were cultured on antibiotic-supplemented and standard MacConkey agar plates and incubated aerobically at 35 1C for up to 48 h.
Epidemiological patterns of A. baumannii and S. maltophilia acquisition
Case-control study design In order to identify the individual risk factors for acquiring an infection a case-control study was designed for patients with or without infection sustained by each of the two microrganisms in study, separately: case patients were all those with NI diagnosis, while control
During the study period, 121 consecutive patients were enrolled in the study. A total of 47 A. baumannii isolates were identified from 21 patients (17.3%, 21 over 121 patients) and a total of 45 S. maltophilia isolates from 21 patients (17.3%, 21 over 121 patients). A total of 9 patients were colonized and/or infected by both pathogens. A total of 31 colonization episodes were identified in 25 different patients and 31 infections were identified in 22 different patients with at least one of the emerging pathogens in study. Total and pathogenspecific ICU-acquired colonization and infection rates are reported in Table 1.
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Table 1.
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Epidemiological patterns of A. baumannii and S. maltophilia acquisition A. baumannii
S. maltophilia
Total
Number of isolates Carriage at admission (/100 patients) ICU-acquired colonization (/100 patients) Incidence density of colonization (/1000 patient-days) ICU-acquired infection (/100 patients) Incidence density of infection (/1000 patient-days)
47 0 14.9 8.3 13.2 7.4
45 0 10.7 6.0 12.4 6.9
92 0 25.6 14.3 25.6 14.3
Genotyping
Table 2.
Microrganism
Number of crosstransmission episodes of infection and colonization (number of infections and colonizations)
Impact of crosstransmission of infection and colonization (%)
A. baumannii S. maltophilia
18 (34) 17 (28)
52.9 60.7
Total
35 (62)
56.4
10
S. maltophilia
8 7 6 5 4 3 2 1 0
Antimicrobial resistance
A. baumannii
9
Number of infections
All A. baumannii isolates identified by the Phoenix system had the combined ARDRA profile for the respective enzymes CfoI, AluI, MboI, RsaI and MspI, which, according to the library of profiles of reference strains, confirmed at the molecular level the organisms as A. baumannii. A total of 60 strains, 33 A. baumannii and 27 S. maltophilia isolates, were subjected to macrorestriction analysis. A single PFGE-type with four distinct subtypes was shown among the A. baumannii isolates, thus the spread of a unique epidemic clone was demonstrated. Four distinct clones were identified among the S. maltophilia isolates, all associated with crosstransmission of infection and/or colonization; a major clone (named clone A) was responsible for the epidemic spread of S. maltophilia (55.5% of isolates), followed by clone D (25.9%), clone B (11.1%) and clone C (7.5%). Clone A was significantly associated to infection (90.9% of events) rather than to colonization (9.1% events) po0.05. The impact of cross-transmission due to A. baumannii and S. maltophilia infection was estimated to be at least 64.5% of all infections. When cross-transmission of colonization was included the impact of cross-transmission was at least 56.4% (Table 2).
Cross-transmissions by microorganism
Jan
Feb
Mar
Apr
May
Jun
July
Months
All A. baumannii and S. maltophilia isolates were MDR. Particularly, all A. baumannii isolates were sensitive to carbapenems and 97.8% of S. maltophilia isolates were resistant to ciprofloxacin. In particular, S. maltophilia clone A (15 isolates) displayed high resistance to fluoroquinolones, that is 100% to ciprofloxacin and 66.7% to levofloxacin, but was 100% sensitive to trimethoprim/sulphamethoxazole.
Epidemic curves and outbreak investigation The specific epidemic curves were constructed to plot the occurrence of both microrganism-associated
Fig. 1. Number of infections by microrganism over the time period.
infection and colonization events (Fig. 1 and data not shown, respectively). The curves suggest the occurrence of an outbreak sustained by the two pathogens involving a total of 33 patients (27.3% of all enrolled patients). The shape of each curve, containing two peaks, suggests a propagated or progressive-source mode of epidemic transmission, reflective of the number of cases caused by person-to-person contact. The outlier analysis led to the identification of potential sources of the two pathogens: a burn patient,
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from a different hospital, colonized on ICU admission by S. maltophilia clone C and a patient who became colonized by A. baumannii during ICU stay. All environmental cultures were taken at midoutbreak period and resulted negative for A. baumannii and S. maltophilia. When the outbreak was identified, at the beginning of March, a multimodal infection control program was introduced in order to control the acquisition and spread of A. baumannii and S. maltophilia in the ICU, including review of all healthcare procedures, training of staff in the correct washing of hands, introduction of alcohol-based antiseptic gel, enhanced cleaning and disinfection of medical equipment and wards and use of single-patient medical instruments. In the 4 months following the implementation of the above-described measures, a decrease in the incidence of recovery of new A. baumannii and S. maltophilia isolates from patients was observed, and subsequently no new cases of A. baumannii and S. maltophilia were reported in our unit.
to length of mechanical ventilation (Table 3). Multivariate logistic regression analysis was used to adjust for possible confounding effects. Mechanical ventilation for the entire length of stay against exposure for part of patient stay remained statistically significant in the final models for A. baumannii (OR 8.1; 95%C.I.: 1.7–38.8) and for S. maltophilia (OR 9.9; 95%C.I.: 2.0–48.2) infections. Univariate analysis showed that infection due to at least one microrganism was significantly associated with length of mechanical ventilation and with surgical procedure (Table 3). Mechanical ventilation for the entire length of stay (OR 8.4; 95%C.I.: 2.6–27.5) and exposure to surgical procedures prior to ICU admission (OR 4.8; 95%C.I.: 1.0–23.4) remained statistically significant in the final model of multivariate analysis. Furthermore, the 24-h nurse-to-patient ratio resulted greater than 1 during the entire period of the survey (median 1.3, range 1.2–1.6). Thus, no association between the nurse-to-patient ratio and the outbreak was shown in our study.
Risk factor analysis
Discussion
Univariate analysis showed that A. baumannii infection was significantly related to chronic renal insufficiency and to the length of mechanical ventilation. S. maltophilia infection was significantly related to surgical procedure, to chronic renal insufficiency and
The aim of our study was to investigate the genotyping of A. baumannii and S. maltophilia, their genetic relatedness and epidemiological links, their mode of transmission and the patients’ risk profile for their acquisition at the ICU of an Italian Hospital.
Table 3.
Risk factors for infection by univariate analysis
Variables
A. baumannii
Dead in the ICU Mechanical ventilation (entire length of stay) Central venous catheter (entire length of stay) Nasogastric tube (entire length of stay) Urinary Catheter (entire length of stay) Surgical procedures (Yes) Diabetes (Yes) Chronic renal insufficiency (Yes) Chronic pulmonary disease (Yes) Neoplastic disease (Yes)
S. maltophilia
At least one microorganism
Case patients (%) (N ¼ 13)
Control patients (%) (N ¼ 108)
pValue
Case patients (%) (N ¼ 13)
Control patients (%) (N ¼ 108)
pValue
Case patients (%) (N ¼ 22)
Control patients (%) (N ¼ 99)
pValue
50.0 83.3
23.8 38.1
0.800 0.004
38.5 84.6
25.0 37.5
0.325 0.002
42.9 81.0
22.9 34.4
0.098 0.000
75.0
81.9
0.695
69.2
82.7
0.263
66.7
84.4
0.071
91.7
97.1
0.360
84.6
98.0
0.062
85.7
98.9
0.119
91.7
88.6
1.000
84.6
89.4
0.637
85.7
89.6
0.701
84.6
70.4
0.348
68.5
0.019
90.9
67.7
0.035
38.5 31.5
16.3 10.5
0.068 0.016
38.5 46.2
16.3 14.3
0.068 0.012
31.8 18.2
15.8 11.5
0.126 0.476
8.3
16.3
0.688
9.1
16.2
1.000
5.3
17.5
0.299
7.7
13.1
1.000
15.4
12.1
0.666
13.6
12.2
1.000
1.000
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Our study provided evidence for the occurrence of an outbreak sustained by A. baumannii and S. maltophilia involving 27.3% of patients enrolled into the surveillance. The epidemic spread of A. baumannii confirmed the role of cross-transmission as a common mechanism of acquisition of such nosocomial pathogen also in our geographic area (Agodi et al., 2006; Zarrilli et al., 2007). Conversely, cross-infection with S. maltophilia is not common, and only a few clones have been associated to transmission among different patients, producing outbreaks and epidemics (Abbassi et al., 2008; Crispino et al., 2002; Gu¨lmez and Hasc¸elik, 2005; Valdezate et al., 2004). Besides, it has been reported that S. maltophilia isolates display high genetic diversity, even when isolated in a single hospital. This is indicative of the polyclonal nature of emergence of these resistant bacteria and may be related to the wide environmental distribution of this pathogen (Tan et al., 2007). Notably, in our ICU we were able to identify a major S. maltophilia clone, accounting at least for 55.5% of all isolates, responsible for the epidemic spread of this microrganism. In general, the estimated proportion of cases resulting from transmission may vary depending on the occurrence of outbreaks in the period of study (Mikolajczyk et al., 2007). In our study the proportion of NIs as a result of cross-transmission of the two pathogens in study accounted for 64.5% of the total number of ICU-acquired infections, the highest figures reported so far by analogous studies (Grundmann et al., 2005; Halwani et al., 2006; Weist et al., 2002). In our study colonization was shown to represent a considerable part of the bacterial load within the ICU, which would not have been discovered without our specifically focused surveillance program (Abbassi et al., 2008; Rodriguez-Bano et al., 2004). Besides, S. maltophilia major clone, was significantly associated to infection rather than to colonization, thus suggesting to bear specific virulence traits that need to be further characterized. However, the fact that two patients share an organism belonging to the same clone does not necessarily mean that a cross-transmission event did occur; acquisition from a common environmental reservoir, which is fairly common with these organisms, may also have occurred. In the absence of evidences of environmental contamination, transient hand carriage by the ICU personnel was suspected to be the mode of transmission. Moreover, analysis of the outbreak outliers led to the identification of a burn patient from a different hospital colonized on ICU admission by S. maltophilia and a patient who became colonized by A. baumannii during ICU stay as the probable epidemic sources. Strain delineation by the means of molecular methods proved essential in establishing the epidemiologic characteristics of infection due to such organisms and in designing
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rational control measures. Thus, colonization was confirmed to represent not only a considerable element of the bacterial load within the ICU but also a continuous potential source of cross-transmission of specific successful clones. Patients colonized at admission can introduce the pathogen into hospital units. If screened at admission, these patients can be detected and isolated, thus reducing the risk of transmission for others. Such active screening of all or just high-risk patients is standard procedure in some settings but not in others. Anyway, wherever cross-transmission is an indicator of poor quality of care, infection control policies should be improved and identification of alert organisms should trigger additional control measures (van Belkum et al., 2007). The early detection of colonized or infected patients and the prompt implementation of infection control measures are significant factors in the control of bacterial spread. Besides, several cohort studies with a before–after design demonstrated a substantial reduction in infection rates by introducing multimodal infection control programs (Gastmeier, 2007). In our unit, a series of measures was taken to implement hygiene norms and ensure compliance with them. Although our study was not intended to investigate the infection control efficacy, our multimodal program, implemented when the outbreak was identified, that is at the beginning of March, was followed in later months with a drastic restriction of infection and colonization due to A. baumannii and S. maltophilia and subsequently with the successful control of the outbreak. Elucidation of the risk factors associated with the acquisition of MDR A. baumannii and S. maltophilia has been related to a large number of variables. Mechanical ventilation is an established risk factor for crosstransmission and it has been suggested that a longer patients’ time exposure increases the chance of infection (Halwani et al., 2006; van der Kooi et al., 2007). In the present study, those patients who were ventilated for the entire length of stay were shown to be at higher risk of infection compared with those at risk for a portion of their length of stay. Regular monitoring of mechanically ventilated patients requires they to be touched repeatedly, thus increasing the risk of cross-transmission when proper hand hygiene is lacking. Exposure to surgical procedures prior to ICU admission was shown to increase nearly five-fold the risk of infection, as already reported elsewhere (Giamberardino et al., 2007; Meric et al., 2005; Ponce de Leo´n-Rosales et al., 2000). In conclusion, the present study described an integrated approach, consisting of active surveillance of infection and colonization by high-risk clones, together with implementation of control strategies, including strict hand hygiene, and the effective control of the epidemic spread of both alert pathogens in the ICU.
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Acknowledgements This work was supported by grants from the University of Catania, Italy (Progetti di Ricerca di Ateneo to A.A.). This study was presented, in part, at the 17th European Congress of Clinical Microbiology and Infectious Diseases, 31 March–3 April 2007, Munich, Germany.
References Abbassi, M.S., Touati, A., Achour, W., Cherif, A., Jabnoun, S., Khrouf, N., Ben Hassen, A., 2008. Stenotrophomonas maltophilia responsible for respiratory infections in neonatal intensive care unit: antibiotic susceptibility and molecular typing. Pathol. Biol. 3. Agodi, A., Zarrilli, R., Barchitta, M., Anzaldi, A., Di Popolo, A., Mattaliano, A., Ghiraldi, E., Travali, S., 2006. Alertsurveillance of ICU-acquired Acinetobacter infections in a Sicilian hospital. Clin. Microbiol. Infect. 12, 241–247. Agodi, A., Barchitta, M., Cipresso, R., Giaquinta, L., Romeo, M.A., Denaro, C., 2007. Pseudomonas aeruginosa carriage, colonization, and infection in ICU patients. Intensive Care Med. 33, 1155–1161. Bertrand, X., Thouverez, M., Talon, D., et al., 2001. Endemicity, molecular diversity and colonisation routes of Pseudomonas aeruginosa in intensive care units. Intensive Care Med. 27, 1263–1268. CDC, 1992. Principles of Epidemiology, second ed. Public Health Practice Program Office, Atlanta, GA. Clark, N.M., Patterson, J., Lynch III, J.P., 2003. Antimicrobial resistance among gram-negative organisms in the intensive care unit. Curr. Opin. Crit. Care 9, 413–423. Crispino, M., Boccia, M.C., Bagattini, M., Villari, P., Triassi, M., Zarrilli, R., 2002. Molecular epidemiology of Stenotrophomonas maltophilia in a university hospital. J. Hosp. Infect. 52, 88–92. Denton, M., Todd, N.J., Kerr, K.G., Hawkey, P.M., Littlewood, J.M., 1998. Molecular epidemiology of Stenotrophomonas maltophilia isolated from clinical specimens from patients with cystic fibrosis and associated environmental samples. J. Clin. Microbiol. 36, 1953–1958. Dijkshoorn, L., van Harsselaar, B., Tjernberg, I., Bouvet, P.J.M., Vaneechoutte, M., 1998. Evaluation of amplified ribosomal DNA restriction analysis for identification of Acinetobacter genomic species. Syst. Appl. Microbiol. 21, 33–39. Gastmeier, P., 2007. Evidence-based infection control in the ICU (except catheters). Curr. Opin. Crit. Care 13, 557–562. Giamberardino, H.I., Cesa´rio, E.P., Carmes, E.R., Mulinari, R.A., 2007. Risk factors for nosocomial infection in trauma patients. Braz. J. Infect. Dis. 11, 285–289. Grundmann, H., Barwolff, S., Tami, A., et al., 2005. How many infections are caused by patient-to-patient transmission in intensive care units? Crit. Care Med. 33, 946–951. Gu¨lmez, D., Hasc¸elik, G., 2005. Stenotrophomonas maltophilia: antimicrobial resistance and molecular typing of an
emerging pathogen in a Turkish university hospital. Clin. Microbiol. Infect. 11, 880–886. Halwani, M., Solaymani-Dodaran, M., Grundmann, H., Coupland, C., Slack, R., 2006. Cross-transmission of nosocomial pathogens in an adult intensive care unit: incidence and risk factors. J. Hosp. Infect. 63, 39–46. Hugonnet, S., Chevrolet, J.C., Pittet, D., 2007. The effect of workload on infection risk in critically ill patients. Crit. Care Med. 35, 76–81. McGowan, J.E., 2006. Resistance in nonfermenting gramnegative bacteria: multidrug resistance to the maximum. Am. J. Infect. Control 34, S29–S37. Meric, M., Willke, A., Caglayan, C., Toker, K., 2005. Intensive care unit-acquired infections: incidence, risk factors and associated mortality in a Turkish university hospital. Jpn. J. Infect. Dis. 58, 297–302. Meyer, E., Schwab, F., Gastmeier, P., Rueden, H., Daschner, F.D., Jonas, D., 2006. Stenotrophomonas maltophilia and antibiotic use in German intensive care units: data from Project SARI. J. Hosp. Infect. 64, 238–243. Mikolajczyk, R.T., Sagel, U., Bornemann, R., Kramer, A., Kretzschmar, M., 2007. A statistical method for estimating the proportion of cases resulting from cross-transmission of multi-resistant pathogens in an intensive care unit. J. Hosp. Infect. 65, 149–155. Ponce de Leo´n-Rosales, S.P., Molinar-Ramos, F., Domı´ nguez-Cherit, G., Rangel-Frausto, M.S., Va´zquez-Ramos, V.G., 2000. Prevalence of infections in intensive care units in Mexico: a multicenter study. Crit. Care Med. 28, 1316–1321. Rodriguez-Bano, J., Cisneros, J.M., Fernandez-Cuenca, F., et al., 2004. Clinical features and epidemiology of Acinetobacter baumannii colonization and infection in Spanish hospitals. Infect. Control Hosp. Epidemiol. 25, 819–824. Schreckenberger, P., Daneshvar, M., Weyant, R.S., Hollis, D., 2003. Acinetobacter, Achromobacter, Chryseobacterium, Moraxella, and other nonfermentative gram-negative rods. In: Murray, P.R., Baron, E.J., Jorgensen, J.H., Pfaller, M.A., Yolken, R.H. (Eds.), Manual of Clinical Microbiology, eighth ed. ASM Press, Washington, DC, pp. 749–779. Suetens, C., Morales, I., Savey, A., et al., 2007. European surveillance of ICU-acquired infections (HELICS-ICU): methods and main results. J. Hosp. Infect. 65, S171–S173. Tan, C.K., Liaw, S.J., Yu, C.J., Teng, L.J., Hsueh, P.R., 2007. Extensively drug-resistant Stenotrophomonas maltophilia in a tertiary care hospital in Taiwan: microbiologic characteristics, clinical features, and outcomes. Diagn. Microbiol. Infect. Dis. 18. Tenover, F.C., Arbeit, R.D., Goering, R.V., et al., 1995. Interpreting chromosomal DNA restriction patterns produced by pulsed field gel electrophoresis: criteria for bacterial strain typing. J. Clin. Microbiol. 33, 2233–2239. Turton, J.F., Gabriel, S.N., Valderrey, C., Kaufmann, M.E., Pitt, T.L., 2007. Use of sequence-based typing and multiplex PCR to identify clonal lineages of outbreak strains of Acinetobacter baumannii. Clin. Microbiol. Infect. 13, 807–815. Valdezate, S., Vindel, A., Martı´ n-Da´vila, P., Sa´nchez Del Saz, B., Vaquero, F., Canto, R., 2004. High genetic diversity among Stenotrophomonas maltophilia strains despite their
ARTICLE IN PRESS M. Barchitta et al. / Int. J. Hyg. Environ. Health 212 (2009) 330–337
originating at a single hospital. J. Clin. Microbiol. 42, 693–699. van Belkum, A., Tassios, P.T., Dijkshoorn, L., et al., 2007. Guidelines for the validation and application of typing methods for use in bacterial epidemiology. Clin. Microbiol. Infect. 13, 1–46. van der Kooi, T.I.I., de Boer, A.S., Mannie¨n, J., et al., 2007. Incidence and risk factors of device-associated infections and associated mortality at the intensive care in the Dutch surveillance system. Intensive Care Med. 33, 271–278. Vaneechoutte, M., Dijkshoorn, L., Tjernberg, I., et al., 1995. Identification of Acinetobacter genomic species by amplified ribosomal DNA restriction analysis. J. Clin. Microbiol. 33, 11–15.
337
Wang, W.S., Liu, C.P., Lee, C.M., et al., 2004. Stenotrophomonas maltophilia bacteremia in adults: four years’ experience in a medical center in northern Taiwan. J. Microbiol. Immunol. Infect. 37, 359–365. Weist, K., Pollege, K., Schultz, I., Ruden, H., Gastmeier, P., 2002. How many nosocomial infections are associated with cross-transmission? A prospective cohort study in a surgical intensive care unit. Infect. Control Hosp. Epidemiol. 23, 127–132. Zarrilli, R., Casillo, R., Di Popolo, A., et al., 2007. Molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii in a university hospital in Italy. Clin. Microbiol. Infect. 13, 481–489.