Eur J Clin Microbiol Infect Dis (2004) 23:163–167DOI 10.1007/s10096-003-1084-2

A R T I C L E

R. Colodner · W. Rock · B. Chazan · N. Keller ·N. Guy · W. Sakran · R. Raz

Risk Factors for the Development of Extended-SpectrumBeta-Lactamase-Producing Bacteria in Nonhospitalized Patients

Published online: 19 February 2004� Springer-Verlag 2004

Abstract Although the risk factors for acquiring infec-tion by extended-spectrum beta-lactamase (ESBL)-pro-ducing bacteria have been investigated in hospitalizedpatients, such risk factors have not been defined in thecommunity setting. In this study, clinical data from a totalof 311 nonhospitalized patients with community-acquiredurinary tract infection (128 with ESBL-positive strainsand 183 with ESBL-negative strains) were obtained.According to a multivariate analysis, the following wereidentified as independent risk factors: previous hospital-ization in the past 3 months (OR=8.95, 95%CI, 3.77–21.25), antibiotic treatment in the past 3 months (OR=3.23, 95%CI, 1.76–5.91), age over 60 years (OR=2.65,95%CI, 1.45–4.83), diabetes (OR=2.57, 95%CI, 1.20–

5.51), male gender (OR=2.47, 95%CI, 1.22–5.01), Kleb-siella pneumoniae infection (OR=2.31, 95%CI, 1.17–4.54), previous use of third-generation cephalosporins(P=0.014, OR=15.8, 95%CI, 1.7–143), previous use ofsecond-generation cephalosporins (P<0.0001, OR=10.1,95%CI, 4.2–24), previous use of quinolones (P=0.001,OR=4.1, 95%CI, 1.8–9.0), and previous use of penicillin(P=0.003, OR=4.0, 95%CI, 1.6–9.0).

Introduction

Extended-spectrum beta-lactamases (ESBLs) are a het-erogeneous group of enzymes responsible for resistanceagainst extended-spectrum beta-lactam antibiotics [1].The first reports of ESBLs came from Europe [2, 3] andwere followed very quickly by reports in the USA [4, 5].This type of antimicrobial resistance has been recognizedworldwide in the last 20 years.

ESBL-producing bacteria often show cross-resistanceto other groups of antibiotics, like fluoroquinolones. Theclose relationship between ESBL production and cipro-floxacin resistance is particularly worrisome because itnarrows the range of alternative therapy for isolatesharboring both mechanisms at the same time. Suchclinical isolates have already been reported [6].

One of the pillars of infection control is the knowledgeobtained from surveillance studies. Among the dataobtained from such studies performed in hospitalizedESBL-harboring patients, specific risk factors includedlength of hospital stay, severity of illness, time in the ICU,intubation and mechanical ventilation, urinary or arterialcatheterization, previous exposure to antibiotics [7, 8] andurinary tract infection (UTI) [9, 10].

There is little data about the incidence of community-acquired infections caused by ESBL-producing bacteria[11]. In a recent pilot surveillance study, we demonstratedthe presence of ESBL-producing strains causing commu-nity-acquired UTIs in our region [12]. This data must beconfirmed in a larger study.

R. Colodner ())Clinical Microbiology Laboratory,Ha’Emek Medical Center,18101 Afula, Israele-mail: colodner_ra@clalit.org.ilTel.: +972-4649-4480Fax: +972-4649-5428

B. Chazan · W. Sakran · R. RazInfectious Diseases Unit,Ha’Emek Medical Center,18101 Afula, Israel

N. KellerSheba Medical Center,Tel Hashomer, Israel

B. Chazan · N. GuyDepartment of Family Medicine,Ha’Emek Medical Center,18101 Afula, Israel

W. SakranPediatric B Ward,Ha’Emek Medical Center,18101 Afula, Israel

W. Rock · W. Sakran · R. RazThe Rappaport Faculty of Medicine,The Technion,Haifa, Israel

The objective of the present study was to investigatethe risk factors for development of ESBL-producingbacteria in nonhospitalized patients and the role of thesefactors in the spread of this relatively new mechanism ofbacterial resistance in our region.

Materials and Methods

Nonhospitalized patients with community-acquired UTI due toEscherichia coli or Klebsiella spp. were included in the study.Urine cultures growing more than 104 colony-forming units (cfu)per milliliter were considered positive, according to the urineculture protocol in use at the Ha’Emek Medical Center, amodification of the protocol recommended in the Cumitech 2Bmanual [13].

In order to find the study group patients, all isolates from urinecultures positive for gram-negative bacteria and received in aperiod of 2 years in the microbiology laboratory of Ha’EmekMedical Center were identified to the species level. Strains werethen tested for antimicrobial susceptibility and were also screenedfor ESBL production using Microscan Gram-Negative ComboUrine panels Type 2 (Dade-Behring, USA) and a MicroscanWalkaway 96 apparatus. The presumptive presence of ESBL wasdetermined using the Microscan DMS software and the MicroscanESBL algorithm.

Once a strain was suspected as an ESBL producer, ESBLproduction was confirmed using two ESBL E test strips (ABBiodisk, Sweden) containing ceftazidime and cefotaxime with andwithout clavulanate, according to the manufacturer’s recommen-dations. A strain was defined as an ESBL producer when theminimal inhibitory concentration (MIC) in the presence of clavu-lanic acid was at least eight times lower than the MIC withoutclavulanic acid [14].

Patients with urine cultures that grew ESBL-negative Escher-ichia coli or Klebsiella spp. strains that were consecutively receivedin the laboratory were included in the control group.

Every patient’s treating physician filled out a questionnaire thatincluded the following information: age, gender, underlying dis-eases (diabetes, cardiovascular diseases, gastrointestinal diseases,genitourinary diseases, recurrent UTIs, neurological diseases, ear-nose-throat diseases, malignancies), use of antibiotics in the past 3months, duration of treatment and class of antibiotic used, previoushospitalization in the past 3 months, and duration of any hospital-ization within the past 3 months.

Statistical Analysis

Data analysis was performed using the Pearson chi-square test;Fisher’s exact test was used for small numbers. For antibiotictreatment comparisons, the Mann-Whitney test was used. Amultivariate analysis was performed for all significant unilateralvariables, with results presented as odd ratios with 95% confidenceintervals.

Results

Of a total of 311 cultures, 128 grew ESBL-producingbacteria and were included in the ESBL-producing group.Of these, 74 (57.8%) were Escherichia coli and 54(42.2%) Klebsiella spp. Another 183 grew ESBL-negativeorganisms and were included in the ESBL-negativegroup: 149 were Escherichia coli (81.4%) and 34(18.6%) Klebsiella spp. The mean age of the study group,61.5 years (range, 1–92), was significantly higher thanthat of the control group, 46.4 years (range, 0.2–92). Thelength of antibiotic treatment in the last 3 months was alsosignificantly higher in the ESBL-producing group (meanvalues, 21.6 days vs. 12.3 days for ESBL-producing andESBL-negative groups, respectively).

In addition, as shown in Table 1, patients in the studygroup apparently stayed in the hospital for a longer period(6.28 days vs. 3.75 days). However, this difference wasnot significant (P=0.201), due to a non-Gaussian distri-bution (the median was 5 days for both groups). Of thetotal 311 patients, 71 were male and 240 were female.However, the ESBL-producing group included a signif-icantly higher number of males (P<0.0001). Table 1 alsoshows the prevalence of three other risk factors for bothgroups: previous hospitalization, gender, and age over 60years. When the prevalence rates were compared betweenthe two groups, all three factors showed very significantdifferences (P<0.0001). Fifty-seven patients in the studygroup were previously hospitalized within the period of 3months prior to development of ESBL-positive UTI,compared to only eight patients in the control group.

The list of underlying diseases in both groups ispresented in Table 2. Of all diseases recorded, only forgastrointestinal and ear-nose-throat diseases were signif-icant differences between both groups not observed.Statistical significance of differences between groups wasmore remarkable for diabetes, cardiovascular, genitouri-nary, and neurological diseases.

The same table shows the number of underlyingdiseases as a predictor of ESBL production. As shown inthe table, the predictive value for the production of ESBLincreased together with the number of underlying diseases(positive predictive value, 38.2%, 53.4%, and 65.5% for1, 2, and 3 diseases respectively)

A total of 177 patients received antibiotics in the past 3months. Table 3 shows the use of different antibioticclasses by patients in both groups. When the groups were

Table 1 Demographic and clinical characteristics of the patients included in the study

Characteristic ESBL-positive group (n=128) ESBL-negative group (n=183) P value

Mean age in years €SD (range) 61.5€22.9 (1–92) 46.4€24.9 (0.2–92) <0.0001Percent infected with E. coli 57.8 (n=74) 81.4 (n=149) <0.0001Percent infected with Klebsiella spp. 42.2 (n=54) 18.6 (n=34) <0.0001Mean duration of hospitalization in days €SD (range) 6.28€5.4 (1–32) 3.75€1.75 (1–5) 0.201Mean duration of antibiotic treatment in days €SD (range) 21.6€5.4 (2–90) 12.3€17.2 (1–90) <0.0001Percent hospitalized in the last 3 months 44.5 (n=57) 4.4 (n=8) <0.0001Percent male gender 35.9 (n=46) 13.7 (n=25) <0.0001Percent aged >60 years 69.5 (n=89) 35.2 (n=64) <0.0001

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compared, very significant differences were observed inthe use of penicillin, second-generation cephalosporins,and quinolones (P<0.0001 for all). Lesser but stillsignificant differences were observed with third-genera-tion cephalosporins. However, it should be noted that onlyeight patients received this antibiotic class in the past 3months. Finally, no significant differences were observedwith the use of first-generation cephalosporins, macro-lides, nitrofurantoin, and trimethoprim-sulfamethoxazole.

Table 4 shows the results of a multivariate analysis ofall significant risk factors for the development of ESBL-producing strains. The following were identified asindependent risk factors: previous hospitalization in thepast 3 months, antibiotic treatment in the past 3 months,age over 60 years, diabetes, male gender, and infection

with Klebsiella spp. The calculated positive predictivevalue of all those risks together was 66.4% and thenegative-predictive value 89.6%. Regarding previousantibiotic treatment, second- and third-generation cepha-losporins, quinolones, and penicillin were also identifiedas independent risk factors.

Discussion

Most patients with community-acquired bacterial infec-tions are treated empirically. Thus, when treatmentprotocols are designed, the prevalence of ESBLs amongclinical isolates must be taken into consideration. Yet,such prevalence rates vary from country to country and

Table 3 Univariate analysis ofthe use of antibiotics in the past3 months

Antibiotic class Percent (no.) P value

ESBL-positive group ESBL-negative group

Any antibiotic 78 (100) 42 (77) <0.00011st-generation cephalosporins 3.9 (5) 8.7 (16) 0.0942nd-generation cephalosporins 39.1 (50) 5.5 (10) <0.00013rd-generation cephalosporins 5.5 (7) 0.5 (1) 0.009Macrolides 5.5 (7) 3.8 (7) 0.49Penicillin 23.4 (30) 7.1 (13) <0.0001Quinolones 30.5 (39) 8.7 (16) <0.0001TMP-SMX 3.9 (5) 5.5 (10) 0.53Nitrofurantoin 15.6 (20) 10.4 (19) 0.17Aminoglycosides 2.3 (3) 0 (0) 0.069

TMP-SMX, trimethoprim-sulfamethoxazole

Table 4 Multivariate analysisof all risk factors, ranked bylogistic regression

Risk factor P value Odds ratio 95%CI

Lower Upper

Treatment with 2nd-generation cephalosporins <0.0001 15.8 1.7 143.0Treatment with 3rd-generation cephalosporins 0.009 10.1 4.2 24.0Hospitalization in the last 3 months <0.0001 8.95 3.77 21.25Treatment with quinolones <0.0001 4.1 1.8 9.0Treatment with penicillin <0.0001 4.0 1.6 9.0Antibiotic treatment in the last 3 months <0.0001 3.23 1.76 5.91Age >60 years <0.0001 2.65 1.45 4.83Diabetes <0.0001 2.57 1.20 5.51Male gender <0.0001 2.47 1.22 5.01Infection with Klebsiella spp. <0.0001 2.31 1.17 4.54

Table 2 Underlying diseasesby univariate analysis

Disease Percentage (no.) P value PPV (%)

ESBL-positive group ESBL-negative group

Diabetes 33.6 (43) 9.8 (18) <0.0001Cardiovascular 43.0 (55) 13.7 (25) <0.0001Gastrointestinal 18.0 (23) 12.0 (22) 0.1Genitourinary 35.9 (46) 16.4 (30) <0.0001Recurrent UTI 57.0 (73) 42.1 (77) 0.006Neurological 30.5 (39) 11.5 (21) <0.0001Ear-nose-throat 4.7 (6) 4.4 (8) 0.55Malignancies 14.1 (18) 4.4 (8) 0.0021 underlying disease 22.7 (29) 25.8 (47) <0.0001 38.22 underlying diseases 24.2 (31) 14.8 (27) <0.0001 53.43 underlying diseases 44.5 (57) 16.5 (30) <0.0001 65.5

PPV, positive predictive value

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from region to region. In addition, some institutionsserving regions with low levels of ESBL may not find itcost-effective to test for this resistance mechanism on aroutine basis. All these reasons make the definition of riskfactors for the development of ESBL-producing bacteriaat the community level a major concern.

Unfortunately, the data concerning risk factors for thedevelopment of infection by ESBL-producing bacteriaamong outpatients is very scarce. Recently, Borer et al.[15] conducted a study in southern Israel in which theprevalence and clinical features of community-acquiredbacteremia involving ESBL-producing Enterobacteri-aceae were evaluated. In their study, age, hospitalizationin an intensive care unit, urinary catheterization, and bed-ridden conditions were significant risk factors for ESBLproduction [15]. Their report was the first to describecommunity-acquired Enterobacteriaceae bacteremia in-volving ESBL-producing strains in Israel, and theirfindings suggest that ESBL producers have already begunto disseminate in our community. However, the smallnumber of ESBL-positive patients (only 6) makes con-clusions very problematic in terms of statistical validity.In our study, we analyzed data from a much greaternumber of patients: 128 with community-acquired UTIwho developed infections due to ESBL-producing uro-pathogens, compared to 183 infected with non-ESBL-producing bacteria.

Klebsiella spp. remain the predominant organismsharboring ESBL worldwide. In our study, the percentageof Klebsiella spp. within the ESBL-positive group(42.2%) was significantly higher (P<0.0001) than in thecontrol group (18.6%). In addition, as shown in Table 4,UTI with Klebsiella spp. was identified as an independentrisk factor for the development of infection by ESBL-producing bacteria.

Age was another significant risk factor. As shown inTable 1, patients in the ESBL-producing group weremuch older. In a multivariate analysis, age over 60 yearswas found to be an independent risk factor for infectionby ESBL-producing bacteria. In addition, we found asignificant increase (P<0.0001) in the number of males,from 13.7% in the ESBL-negative group to 35.9% in theESBL-producing group, and male gender was identifiedas another independent risk factor in the multivariateanalysis. The main reason for this gender effect may bethat elderly males develop complicated UTI more fre-quently than elderly women [16]. Another possibleexplanation may be the increased number of underlyingdiseases among the males in our study, which was in itselfanother significant risk factor.

Among the underlying diseases recorded, diabetes,heart diseases, genitourinary, neurological diseases, re-current UTI, and malignancies were significantly morefrequent in the ESBL-positive group, and the risk ofdeveloping infection with ESBL-producing strains in-creased with the increasing number of underlying diseases(2 or more). However, when a logistic regression analysisof all underlying diseases was performed, only diabetes

was identified as an independent risk factor for infectionwith ESBL-producing strains.

Hospitalization has been widely reported as a majorcause of the development of infection by ESBL-produc-ing bacteria, and this was corroborated in our study:previous hospitalization in the past 3 months was iden-tified as the strongest independent risk factor in thelogistic regression analysis. However, our findings sug-gest that patients can also develop infection with ESBL-producing strains in the community: 71 (55.5%) patientsin the ESBL-positive group were not hospitalized in thepast 3 months.

The length of hospitalization proved to be irrelevant inour study. On the contrary, Bisson et al. [17] reported thatduration of hospitalization was the only independent riskfactor for colonization with ESBL-producing Escherichiacoli or Klebsiella spp. However, their study analyzed datafrom a small number of patients (n=13), 8 (62%) of whomwere admitted from another healthcare facility.

In our study, a total of 177 patients received antibiotictreatment during the 3-month period prior to UTI with anESBL-producing strain. Patients in the ESBL-positivegroup were treated with antibiotics for a longer period oftime compared to the ESBL-negative group. Moreover,antibiotic use in the past 3 months was identified as amajor independent risk factor for the development ofinfection by ESBL-producing bacteria, ranked secondafter previous hospitalization. When antibiotic classesused in pretreatment were analyzed, macrolides, trimeth-oprim-sulfamethoxazole, nitrofurantoin, and aminoglyco-sides proved not to be statistically relevant as risk factors.Regarding trimethoprim-sulfamethoxazole, our findingsdiffer from those of Wiener et al. [18], who found use ofthis drug to be an independent risk factor. These findingsare encouraging, since the first three drugs are widelyused at the community level. In addition, nitrofurantoin isthe first-choice drug in the treatment of community-acquired UTI and, as we have shown in the past,resistance rates are still very low in our region [12].

Surprisingly, treatment with first-generation cephalos-porins did not show any risk for developing an infectionby ESBL-producing bacteria, since other cephalosporinsand even penicillins were found to be statisticallyrelevant. As shown in Table 3, significant differenceswere found when the use of second- and third-generationcephalosporins, penicillin, and quinolones in both patientgroups were compared, and these four antibiotics classeswere found to be independent risk factors in the multi-variate analysis.

The selective pressure of third-generation cephalos-porins for selection of ESBL-producing mutants has beenwidely described. Moreover, reduction in their use andbarrier precautions markedly reduced the incidence ofcolonization and infection [19]. In our study, few patientsreceived antibiotics from this class in the past 3 months,because third-generation cephalosporins are not usedmuch at the community clinic level. However, oralsecond-generation cephalosporins like cefuroxime axetilare widely used in outpatient treatment.

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The relationship shown in this study between the useof penicillin and the development of ESBL-producingstrains is a major concern, since penicillin remains thedrug of choice for treatment of streptococcal pharyngitis.However, penicillin is not known as a selective agent forESBL-producing bacteria, and thus the cause for ourfinding should be elucidated.

Quinolones are also widely used in outpatient treat-ment. The fact that quinolones and cephalosporins wereboth identified in our study as independent risk factors forthe development of UTI caused by ESBL-producingbacteria is very frustrating: the remaining treatmentoptions are very limited.

In conclusion, we identified in this study potentialindependent risks for the development of UTI caused byESBL-producing bacteria in our region: infections due toKlebsiella spp., previous hospitalization, previous antibi-otic treatment (especially with second- and third-gener-ation cephalosporins, penicillins, and quinolones), malegender, age over 60 years, and diabetes. The calculatedpositive-predictive value of all these risks factors togetherwas 66.4% and the negative-predictive value 89.6%. Therecognition of these risk factors could aid in the identi-fication of patients at high risk of harboring ESBL-producing pathogens, thus enabling administration ofmore efficient empiric antibiotic treatment.

Acknowledgements The authors thank Idit Lavie for performingthe statistical analysis. This work complies with the current laws ofIsrael regarding clinical trials.

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