International Journal of Infectious Diseases (2008) 12, 171—175
http://intl.elsevierhealth.com/journals/ijid
Risk factors for rectal colonization with vancomycin-resistant enterococci in Shiraz, Iran Mehrdad Askarian a,*, Rahim Afkhamzadeh a, Ahmad Monabbati b, Florian Daxboeck c, Ojan Assadian c a
Department of Community Medicine, Shiraz University of Medical Sciences, PO Box 71345-1737, Shiraz, Iran Department of Pathology, Shiraz University of Medical Sciences, Shiraz, Iran c Department of Hygiene and Medical Microbiology, Medical University Vienna, General Hospital Vienna, Vienna, Austria b
Received 9 October 2006; received in revised form 16 January 2007; accepted 28 April 2007 Corresponding Editor: William Cameron, Ottawa, Canada
KEYWORDS Enterococcus; Vancomycin resistance; VRE; Rectal colonization; Risk factors
Summary Objectives: In order to determine the risk factors for rectal colonization with vancomycin-resistant enterococci (VRE) at the Shiraz Namazi Hospital, we performed a nested case—control study. Methods: From December 2003 to July 2004 rectal swabs were taken from 700 randomly selected hospitalized patients every 5 days. Results: A total of 99 of the 700 patients (14%) were colonized with VRE (cases) and 59 patients were colonized with vancomycin-sensitive strains (VSE), serving as controls. In the univariate analysis, history of antibiotic use ( p = 0.04), underlying disease ( p = 0.013), hemodialysis ( p = 0.03), use of third generation cephalosporins ( p = 0.04), use of vancomycin ( p = 0.04), and duration of vancomycin therapy longer than 7 days ( p = 0.02) were significantly associated with VRE colonization. In a multivariate analysis, underlying disease and the duration of vancomycin use longer than 7 days were independently associated with VRE colonization. Conclusion: Our study, the first on VRE carriage in Iran, demonstrates that VRE prevalence is high in Shiraz and confirms earlier observations in other countries. The identified risk factor ‘use of vancomycin longer than 7 days’ may be avoidable, indicating a feasible intervention strategy in the control of VRE. # 2007 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
Introduction The worldwide observed increase in antimicrobial resistance among pathogens causing nosocomial infections constitutes a
* Corresponding author. Tel.: +98 917 1125777; fax: +98 711 2354431. E-mail address:
[email protected] (M. Askarian).
major public health problem.1 One of the best examples of the bacterial quest for survival are enterococci. For years viewed as harmless inhabitants of the intestinal flora, enterococci have acquired resistance to multiple antibiotics, making glycopeptides like vancomycin one of the last available compounds for therapy. Vancomycin-resistant enterococci (VRE) are among the most feared pathogens in hospitals in the USA. However, the epidemiology of VRE in Europe and America appears to be very different. In contrast to the
1201-9712/$32.00 # 2007 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijid.2007.04.020
172 alarming situation in hospitals in the USA, infections due to VRE remain uncommon in Europe.2 The US National Nosocomial Infection Surveillance (NNIS) system has revealed a significant increase in the percentage of nosocomial Enterococcus spp strains displaying vancomycin resistance. The figure for the incidence of VRE in intensive care unit (ICU) patients rose from 0.4% in 1989 to 23.4% in 1997. In non-ICU patients, the percentage increased from 0.3% to 15.4%, representing a 50-fold increase in a relatively short time span.3 According to data from the NNIS system, enterococci are now the fourth leading cause of nosocomial infections and the third in ICU patients in the USA.1,4,5 Risk factors for VRE colonization may be patient-, hospital-, environment-, and antibiotic-related.1 Although many studies have been performed in Europe and the USA on the prevalence, incidence, epidemiology, and risk factors of VRE, data for the Middle East and Asia are scarce.6 This study is the first investigation on the epidemiology of VRE in Iran. The aim of the present study was to determine the prevalence and risk factors of rectal colonization with VRE in Iranian patients.
Materials and methods Setting The study hospital (Shiraz Namazi Hospital) provides primary and tertiary care in a 750-bed health facility for patients admitted from Shiraz, Fars State and other southern states of Iran. Twenty-five wards participated in this study, including nine ICUs with a total capacity of 50 beds (two neurosurgical ICUs, two medical ICUs, one surgical ICU, one pediatric ICU, one neonatal ICU, and two cardiac care units), five surgical wards with a total of 120 beds (neurosurgery, plastic surgery, general surgery, urology, and trauma), seven medical wards with a total of 135 beds (one cardiology, one female medical ward, one male medical ward, two general medical wards, and two oncology wards), and four pediatric wards with a total capacity of 80 beds (three medical wards and one surgical ward). Currently, there are no VRE-specific infection control strategies implemented in the investigated hospital, and no screening policy or surveillance concepts. There are, however, general measures including hand hygiene and standard precaution concepts, although compliance varies.
Patients All hospitalized patients admitted during the study period (December 2003 through July 2004) with a hospital stay of longer than 5 days (700 patients) were selected for this study.
Study design This study was designed as a nested case—control and descriptive-analytic study to determine the prevalence and risk factors of colonization with VRE. Educated nurses took serial rectal swabs every 5 days. Samples were sent to the laboratory in transportation tubes (Venturi Transystem, Copan Diagnostics Inc., New York, NY, USA). A case patient was defined as any patient who had a positive sample yielding
M. Askarian et al. VRE; a control patient was a patient from whom vancomycinsensitive enterococci (VSE) were yielded. A third group encompassed all patients with repetitive negative Enterococcus spp samples.
Data collection Data from each patient were extracted from the medical records and at the bedside. Obtained data included the following: age, sex, co-morbidity and underlying disease, ward of admission, duration of stay, prior admission, prior antibiotic use, clinical outcome, kind and duration of antibiotic use before colonization, and laboratory results.
Microbiological methods Rectal swab specimens were cultivated on a selective agar and incubated at 37 8C overnight. Cephalexin—aztreonam— arabinose agar (CAA) was prepared by adding 40 g of Columbia agar base (Unipath, Basingstoke, UK), 10 g of arabinose (Sigma Chemical Co., Poole, UK), and 3.6 ml of phenol-red (2%; BDH, Lutterworth, UK) to 1 liter of de-ionized water. The medium was mixed and the pH was adjusted to 7.8. The agar was autoclaved at 114 8C for 20 min. Fresh sterile solutions of aztreonam (Bristol-Myers Squibb, Hounslow, UK) and cephalexin (Sigma) were added to give final concentrations of 75 mg/l and 50 mg/l, respectively.7 Swabs were streaked on the surface of CAA. The plates were incubated at 37 8C in air for 24 h and examined for growth and fermentation of arabinose. A change in the color of the medium surrounding the colony, from red to yellow, indicated arabinose fermentation.
Conventional organism identification and susceptibility testing Red to yellow colonies resembling enterococci on the CAA plates were further identified by conventional laboratory methods, including Gram staining and determination of colonial morphology and biochemical and growth characteristics.8,9 Species identification was performed using API 20 STREP (bioMerieux, Marcy L’Etoile, France). In vitro susceptibility to ampicillin, penicillin, gentamicin, vancomycin, and teicoplanin was tested according to Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS)10 guidelines, using the agar dilution method and Mueller—Hinton agar (Becton Dickinson, Franklin Lakes, USA).
Definitions The presence of the following conditions was documented for underlying disease: immunosuppression, neutropenia, renal failure (as indicated by baseline creatinine level of >0.2 mg/ dl), hemodialysis, cancer, diabetes mellitus, major surgery, severe cardiac disease (as indicated by cardiac heart failure and myocardial infarction), sepsis, and systemic lupus erythematosus (SLE). Prior admission was defined as admission during the six months before the present hospitalization. Prior antibiotic use was defined as the administration of antimicrobials for >72 h during the 60 days before the onset of hospitalization. Duration of antibiotic use before coloniza-
173
Risk factors for rectal colonization with VRE, Iran tion was defined as the number of days of antibiotic use before colonization with VRE or VSE, for antibiotic use of more than 1 day. The duration of hospitalization was the number of days a patient was cared for at the institution determined by enumeration of hospital days per patient, regardless of VRE or VSE status. Colonization was defined as the isolation of VRE or VSE from a rectal swab culture with or without evidence of clinical infection with the yielded organism. A negative baseline culture with more than one positive follow-up culture was considered acquisition.
Statistical analysis Data were analyzed using SPSS (Statistical Package for Social Sciences) software. Qualitative variables were compared by use of Pearson’s Chi-square test or Fisher’s exact test, and quantitative variables were compared by Mann—Whitney Utest. Univariate analysis of risk factors for colonization and acquisition was performed. All p values were on two-sided test ( p < 0.05). A logistic regression model was built to identify risk factors. Variables with p < 0.25 were retained in the final model. Odds ratios and the corresponding 95% confidence intervals were calculated using the results obtained for the maximum likelihood estimates.11
Ethical considerations Informed oral consent was obtained from all study patients prior to specimen collection. Patients who did not permit sampling, or patients for whom the performing of a rectal swab was contraindicated, were not included in the study.
Results During the study period, a total of 700 patients out of a total of 1856 admitted patients were enrolled into the study, yielding more than 1000 rectal swabs (median of swab per patient = 1). The mean age of patients was 36.4 years (range 0.02—92 years); 311 (44.4%) were female. Of these patients, 542 (77.4%) had no colonization. Ninety-nine patients (14.1%) were VRE-colonized (case group) and 59 (8.4%) were VSEcolonized (control group). All 99 VRE positive patients were VRE negative on admission and became colonized during their hospital stay. All VRE isolates were resistant to ampicillin, penicillin, and gentamicin according to CLSI standards. However, none of the VRE positive patients developed infection during the observation time of the study. The results of univariate and logistic regression analysis are shown in Table 1. In the univariate analysis, sex ( p = 0.074), ward ( p = 0.17), duration of hospitalization ( p = 0.11), history of prior hospitalization ( p = 0.16), and clinical outcome ( p = 0.06) were not associated with VRE colonization. However, prior administration of antibiotics (OR 3.09; 95% CI 1.82— 7.64; p = 0.04), underlying disease (OR 2.46; 95% CI 1.23—5.7; p = 0.013), hemodialysis (OR 3.87; 95% CI 1.1—13.8; p = 0.03), use of third generation cephalosporins such as ceftizoxime, ceftriaxone, and cefixim (OR 2.28; 95% CI 1.1—4.9; p = 0.04), vancomycin use (OR 2.53; 95% CI 1.1—5.8; p = 0.04), and duration of vancomycin use longer than 7 days (OR 1.7; 95% CI 1.1—3.4; p = 0.02) showed significant differences between VRE- and VSE-colonized patients.
In the multivariate analysis, significant independent risk factors for VRE versus VSE colonization were only the presence of an underlying disease (OR 2.43; 95% CI 1.2—4.9; p = 0.013) and vancomycin use for longer than 7 days (OR 1.6; 95% CI 1.0—2.5; p = 0.03).
Discussion Vancomycin-resistant Enterococcus faecium and Enterococcus faecalis (VRE) were first described in the UK in 198812 and soon afterwards reported from other European countries13 and the USA.14 Since then, VRE has steadily emerged as an important cause of hospital-acquired infection. Gastrointestinal colonization is the most common source for VRE spreading.15 Although many studies have been conducted on the epidemiology of VRE,16—19 there are few case—control studies determining risk factors for colonization.1,12,20—22 To our knowledge, the present study is the first study on the epidemiology of VRE in Iran. In this study, the mean age of patients showed no significant difference between the three groups — patients without colonization, patients with VRE colonization, and patients with VSE colonization. However, age stratified into four groups showed borderline significance ( p = 0.052), and VRE colonization was highest in patients aged 1—16 years, which is consistent with the findings of previous investigators.23,24 Sex, ward, duration of hospitalization, and prior admission were not significant risk factors for VRE colonization. Other investigators have also confirmed these findings for other parts of the world. van den Braak et al.25 and Tornieporth et al.1 reported that sex was not associated with VRE colonization. From our results the median length of hospitalization before colonization in case and control groups was similar, which is consistent with van den Braak et al.25 and Bertrand et al.,5 but not with Tornieporth et al.1 In our study, all VRE positive patients were VRE negative on admission, and 80% of these patients were colonized early in the first week of hospitalization, indicating that very early nosocomial transmission occurred. Therefore, it is not surprising that duration of hospitalization did not show as a significant risk factor, similar to other studies.2,5,26 Prior use of antimicrobial therapy, including vancomycin and cephalosporin, has been shown to be associated with acquisition of VRE.1,20,22,26—28 In our study, this factor was also significant ( p = 0.04) and increased the risk for VRE colonization 3-fold. Also, the presence of underlying disease was significantly associated with an increased risk for VRE colonization, as was the association between renal failure and hemodialysis. Of note, impaired renal function and hemodialysis have been previously implicated as risk factors in VRE outbreaks.29,30 Although other underlying diseases such as septicemia, immunosuppression, neutropenia, malignancy, diabetes mellitus, lupus, cardiac disease, and major surgery were more frequent in the case group than in controls, these were not significant. However, it can be speculated that a larger sample size would have revealed differences at the 0.05-significance level. In the present study, use of vancomycin or a third generation cephalosporin was a significant risk factor for VRE colonization. The use of vancomycin increased the risk of colonization 2.5-fold and third generation cephalosporins 2fold. These findings are consistent with previously reported findings.20,22,24,28,31
174 Table 1
M. Askarian et al. Risk factors for vancomycin-resistant Enterococcus in hospitalized patients; Shiraz Namazi Hospital, 2004 Frequency (%) or mean SD
Univariate analysis
Cases (N = 99)
Controls (N = 59)
OR (95% CI)
Age
37.8 26.9
36.8 25.9
Stratified age 65 years
5 18 52 24
8 4 36 11
Sex Male Female
50 (50.5) 49 (49.5)
28 (47.5) 31 (52.5)
Ward Specific Surgical Medical Pediatric
8 9 67 15
8 10 30 11
Duration of hospitalization Before colonization Total
6.6 3.3 21.4 18.5
6.3 3.6 18.3 10.5
Prior hospitalization Prior antibiotic use
36 (36.4) 31 (31.3)
15 (25.4) 8 (13.6)
Outcome Dead Cured Ill and alive
13 (13.2) 43 (43.4) 43 (43.4)
8 (13.6) 30 (50.8) 21 (35.6)
Underlying disease Immunosuppression Neutropenia Hemodialysis Cancer Major surgery Diabetes mellitus Cardiac disease Sepsis Systemic lupus erythematosus
75 (75.7) 9 (9.1) 4 (4.0) 17 (17.2) 17 (17.2) 9 (9.1) 12 (12.1) 15 (15.2) 17 (17.2) 6 (6.1)
33 9 2 3 12 4 5 6 4 2
Antibiotics Vancomycin Third generation cephalosporin Aminoglycosides Clindamycin Metronidazole Ciprofloxacin Co-trimoxazole Erythromycin Penicillin
31 83 32 8 30 18 7 2 6
9 (15.3) 41 (69.5) 19 (32.2) 8 (13.6) 21 (35.6) 6 (10.2) 8 (13.6) 1 (1.7) 4 (6.8)
Variable
Logistic regression p
OR (95% CI)
0.800 0.052
(5.1) (18.2) (52.5) (24.2)
p
0.950
(13.6) (6.8) (61.0) (18.6) 0.074
0.170 (8.1) (9.1) (67.7) (15.2)
0.140
(13.6) (16.5) (50.8) (18.6) 0.890 0.120 0.110 3.09 (1.82—7.64)
0.160 0.04 0.060
(31.3) (83.8) (32.3) (8.1) (30.3) (18.2) (7.1) (2.0) (6.1)
(55.9) (15.3) (3.4) (5) (20.3) (6.8) (8.5) (10.2) (8.2) (3.4)
Duration of antibiotics used before colonization >7 days Vancomycin 4.4 12.4 1.4 4.6 Third generation cephalosporin 8.2 9.3 6.2 6.4 Aminoglycosides 3.9 1.1 1.9 3.7 Clindamycin 0.4 1.6 0.6 1.9 Metronidazole 3.4 11.6 3.4 5.7 Ciprofloxacin 2.7 1.3 0.8 2.8 Co-trimoxazole 1.0 4.5 0.9 2.6 Erythromycin 0.2 1.3 0.1 0.5 Penicillin 0.5 2.0 0.6 2.8 OR, odds ratio; CI, confidence interval.
2.46 (1.23—5.7)
0.013 0.300
3.87 (1.1—13.8)
0.030 0.670 0.770 0.600 0.470 0.090 0.710
2.53 (1.1—5.8) 2.28 (1.1—4.9)
0.040 0.040 1.000 0.290 0.590 0.250 0.260 1.000 1.000
1.7 (1.1—3.4)
0.020 0.130 0.820 0.280 0.330 0.180 0.210 0.880 0.850
2.43 (1.2—4.9)
0.013 0.060 0.060
0.390 0.730 0.150
1.6 (1.0—2.5)
0.030 0.780
175
Risk factors for rectal colonization with VRE, Iran In summary, this study demonstrates that the prevalence of VRE is high in Shiraz Namazi Hospital. Univariate analysis suggests that prior antibiotic use, the presence of underlying disease, hemodialysis for renal failure, administration of vancomycin and third generation cephalosporins, and duration of vancomycin use are risk factors for VRE colonization. However, logistic regression showed that only presence of underlying disease, notably patients requiring hemodialysis, and the use of vancomycin are independent risk factors for VRE colonization.
Acknowledgement This study was funded by the deputy for research at the Shiraz University of Medical Sciences (grant number 822000). Conflict of interest: No conflict of interest to declare.
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