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The biocide triclosan is in many consumer products and is a frequent contaminant of wastewater (WW) such that there is concern that triclosan promotes resistance to important antibiotics. This study identified functional mechanisms of triclosan resistance (TCSR) in WW metagenomes, and assessed the frequency of TCSR in WW-derived and clinical isolates of Escherichia coli and Enterococcus spp. Metagenomic DNA extracted from WW was used to profile the microbiome and construct large-insert cosmid libraries, which were screened for TCSR. Resistant cosmids were sequenced and the TCSR determinant identified by transposon mutagenesis. Wastewater Enterococcus spp. (N = 94) and E. coli (N = 99) and clinical Enterococcus spp. (N = 146) and vancomycin-resistant E. faecium (VRE; N = 149) were collected and tested for resistance to triclosan and a comprehensive drug panel. Functional metagenomic screening revealed diverse FabV homologs as major WW TCSR determinants. Resistant clones harboured sequences likely originating from Aeromonas spp., a common WW microbe. The triclosan MIC90s for E. coli, E. faecalis, and E. faecium isolates were 0.125, 32, and 32 mg/L, respectively. For E. coli, there was no correlation between the triclosan MIC and any drug tested. Negative correlations were detected between the triclosan MIC and levofloxacin resistance for E. faecalis, and between triclosan and vancomycin, teicoplanin, and ampicillin resistance for E. faecium. Thus, FabV homologs were the major contributor to the WW triclosan resistome and high-level TCSR was not observed in WW or clinical isolates. Elevated triclosan MICs were not positively correlated with antimicrobial resistance to any drug tested., Competing Interests: Calgary Laboratory Services provided support in the form of salaries for D.L.C. There are no patents, products in development or marketed products associated with this research to declare. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Successful multidrug-resistant clones are increasing in prevalence globally, which makes the ability to identify these clones urgent. However, adequate, easy-to-perform, and reproducible typing methods are lacking. We investigated whether DiversiLab (DL), an automated repetitive-sequence-based PCR bacterial typing system (bioMérieux), is suitable for comparing isolates analyzed at different geographic centers. A total of 39 Escherichia coli and 39 Klebsiella species isolates previously typed by the coordinating center were analyzed. Pulsed-field gel electrophoresis (PFGE) confirmed the presence of one cluster of 6 isolates, three clusters of 3 isolates, and three clusters of 2 isolates for each set of isolates. DL analysis was performed in 11 centers in six different countries using the same protocol. The DL profiles of 425 E. coli and 422 Klebsiella spp. were obtained. The DL system showed a lower discriminatory power for E. coli than did PFGE. The local DL data showed a low concordance, as indicated by the adjusted Rand and Wallace coefficients (0.132 to 0.740 and 0.070 to 1.0 [E. coli] and 0.091 to 0.864 and 0.056 to 1.0 [Klebsiella spp.], respectively). The central analysis showed a significantly improved concordance (0.473 to 1.0 and 0.290 to 1.0 [E. coli] and 0.513 to 0.965 and 0.425 to 1.0 [Klebsiella spp.], respectively). The misclassifications of profiles for individual isolates were mainly due to inconsistent amplification, which was most likely due to variations in the quality and amounts of the isolated DNA used for amplification. Despite local variations, the DL system has the potential to indicate the occurrence of clonal outbreaks in an international setting, provided there is strict adherence to standardized, reproducible DNA isolation methods and analysis protocols, all supported by a central database for profile comparisons.

Extended-spectrum-beta-lactamase (ESBL)-producing Escherichia coli has recently emerged as a major risk factor for community-acquired, travel-related infections in the Calgary Health Region. Molecular characterization was done on isolates associated with infections in returning travelers using isoelectric focusing, PCR, and sequencing for bla(CTX-M)s, bla(TEM)s, bla(SHV)s, bla(OXA)s, and plasmid-mediated quinolone resistance determinants. Genetic relatedness was determined with pulsed-field gel electrophoresis using XbaI and multilocus sequence typing (MLST). A total of 105 residents were identified; 6/105 (6%) presented with hospital-acquired infections, 9/105 (9%) with health care-associated community-onset infections, and 90/105 (86%) with community-acquired infections. Seventy-seven of 105 (73%) of the ESBL-producing E. coli isolates were positive for bla(CTX-M) genes; 55 (58%) produced CTX-M-15, 13 (14%) CTX-M-14, six (6%) CTX-M-24, one (1%) CTX-M-2, one (1%) CTX-M-3, and one (1%) CTX-M-27, while 10 (10%) produced TEM-52, three (3%) TEM-26, 11 (11%) SHV-2, and four (4%) produced SHV-12. Thirty-one (30%) of the ESBL-producing E. coli isolates were positive for aac(6')-Ib-cr, and one (1%) was positive for qnrS. The majority of the ESBL-producing isolates (n = 95 [90%]) were recovered from urine samples, and 83 (87%) were resistant to ciprofloxacin. The isolation of CTX-M-15 producers belonging to clone ST131 was associated with travel to the Indian subcontinent (India, Pakistan), Africa, the Middle East, and Europe, while clonally unrelated strains of CTX-M-14 and -24 were associated with travel to Asia. Our study suggested that clone ST131 coproducing CTX-M-15, OXA-1, TEM-1, and AAC(6')-Ib-cr and clonally unrelated CTX-M-14 producers have emerged as important causes of community-acquired, travel-related infections.

A study was designed to evaluate the ability of the DiversiLab fingerprinting kit, a type of repetitive element PCR (rep-PCR), to identify Escherichia coli clone ST131 producing beta-lactamase CTX-M-15. A set of 53 nonduplicate isolates of extended-spectrum beta-lactamase-producing E. coli underwent rep-PCR, pulsed-field gel electrophoresis, and multilocus sequence typing. The DiversiLab system successfully identified E. coli clone ST131 producing CTX-M-15 and provides a simple standardized typing protocol for monitoring the spread of this clone.

Objectives: Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli have emerged as significant causes of community-onset disease. We sought to identify risk factors for acquiring community-onset ESBL-producing E. coli., Methods: Prospective, population-based surveillance for ESBL-producing E. coli was performed in the Calgary Health Region (population 1.2 million), Canada during a two-year period., Results: 247 patients were identified; 177 (72%; 7.6 per 100,000/year) were community acquired, and 70 (28%; 3.0 per 100,000/year) were healthcare associated. The acquisition risk increased with advancing age. Females were at higher risk as compared to males [relative risk (RR) 4.3; 95% confidence interval (CI), 3.1-6.1] as were urban as compared to rural residents (RR 2.2; 95% CI, 1.4-3.6). A number of co-morbidities increased risk (RR; 95% CI) including requirement for hemodialysis (56.3; 15.1-147.4), urinary incontinence (21.7; 15.0-30.9), cancer (11.1; 7.0-17.0), heart disease (6.5; 4.3-9.7), and diabetes (4.4; 2.6-7.1). Overseas travel overall increased the risk (5.7; 4.1-7.8) and was highest in travelers to India (145.6; 77.7-252.1), the Middle East (18.1; 8.1-35.2), and Africa (7.7; 2.8-17.2)., Conclusions: Advancing age, female gender, co-morbid medical conditions, and foreign travel are important risk factors for developing community-onset ESBL-producing E. coli infections in our region. Emergence of anti-microbial-resistant pathogens is a global concern.

This study was designed to determine the in vitro activities of several antimicrobial agents against well-characterised CTX-M-producing Escherichia coli strains isolated from clinical specimens. Minimum inhibitory concentrations (MICs) were determined for 202 extended-spectrum beta-lactamase (ESBL)-producing E. coli using microbroth dilution and Vitek methods according to Clinical and Laboratory Standards Institute criteria. Molecular characterisation was performed using isoelectric focusing and polymerase chain reaction (PCR) with sequencing, whilst strain relatedness was determined by pulsed-field gel electrophoresis (PFGE) using XbaI. Of the 202 ESBL-producing E. coli, 2 produced VEB-1, 12 produced TEM-52, 32 produced SHV types (including SHV-2 and -12) and 156 produced CTX-M types (including CTX-M-2, -3, -14, -15, -24, -27 and -30). The MIC(50) and MIC(90) (MIC for 50% and 90% of the organisms, respectively) for the antimicrobial agents tested were, respectively: piperacillin/tazobactam (TZP), 32mg/L and >256mg/L; ciprofloxacin, 16mg/L and 32mg/L; gentamicin, 8mg/L and 128mg/L; amikacin, 2mg/L and 16mg/L; ertapenem, 0.03mg/L and 0.12mg/L; imipenem, 0.03mg/L and 0.12mg/L; meropenem, 0.03mg/L and 0.03mg/L; and tigecycline 0.12mg/L and 0.5mg/L. Vitek Legacy and Vitek 2 failed to detect TZP resistance in 91 (90%) and 75 (74%) of 101 TZP-resistant ESBL-producing strains, respectively, especially CTX-M-15-producing isolates that co-produced OXA-1. The carbapenems, amikacin and tigecycline had good in vitro activities against multiresistant CTX-M-producing E. coli. We recommend that laboratories using Vitek should employ alternative susceptibility testing methods for TZP before reporting the activity of this agent against ESBL-producing E. coli.

A study was designed to describe the molecular epidemiology of CTX-M-producing Escherichia coli over a 6-year period (2000 to 2005) in a large well-defined Canadian region with a centralized laboratory system. Molecular characterization was done by isoelectric focusing, PCR, and automated sequencing, while genetic relatedness was determined by pulsed-field gel electrophoresis with XbaI. Of the 552 viable extended-spectrum beta-lactamase-producing E. coli isolates isolated, 354 (64%) were positive for blaCTX-M genes associated with ISEcp1; 211 produced CTX-M-14, 128 produced CTX-M-15, 5 produced CTX-M-2, 4 produced CTX-M-3, 4 produced CTX-M-24, and 2 produced CTX-M-27. CTX-M-positive isolates were significantly more resistant to the fluoroquinolones than CTX-M-negative isolates, while CTX-M-15 producers were more likely to be resistant to gentamicin and tobramycin. There was a predominance of CTX-M-14 during the first 4 years of the study period, with community outbreaks associated with cluster 14A during 2000, 2001, and 2003. A substantial increase in CTX-M-15 producers occurred during the last 18 months and was due to clusters 15A and 15AR (where AR indicates related to A) in the hospital and nursing home sectors. Our results demonstrate that the persistence and dissemination of CTX-M genes among E. coli populations in larger geographic health care regions is dynamic, with the continuous emergence of clonally related CTX-M-15. This study illustrates the importance of molecular surveillance in tracking CTX-M-producing E. coli strains in the community and investigating their influx into hospitals.

In the Calgary Health Region during 2000-2003, prospective, active, population-based laboratory surveillance for all cefoxitin-resistant Escherichia coli isolates was performed. Isolates were screened with an inhibitor-based disk test, and plasmid-mediated types were identified by multiplex PCR with sequencing. A total of 369 AmpC beta-lactamase-producing E. coli isolates were identified; annual incidence rates were 1.7, 4.3, 11.2, and 15 per 100,000 residents for each year, respectively. AmpC beta-lactamase-producing E. coli was 5x more likely to be isolated from female than male patients across all age groups except < 1 year. Of these isolates, 83% were community onset, and urine was the principal site of isolation (90% of patients). PCR showed that 125 (34%) were positive for bla(cmy) genes; sequencing identified these enzymes to be CMY-2. In this large Canadian region, AmpC beta-lactamase-producing E. coli is an emerging community pathogen that commonly causes urinary tract infections in older women.

A ciprofloxacin-resistant Escherichia coli isolate, isolate 1B, was obtained from a urinary specimen of a Canadian patient treated with norfloxacin for infection due to a ciprofloxacin-susceptible isolate, isolate 1A. Both isolates harbored a plasmid-encoded sul1-type integron with qnrA1 and blaVEB-1 genes. Isolate 1B had amino acid substitutions in gyrase and topoisomerase.

This study determined the phylogenetic groups and virulence factors of 37 Escherichia coli isolates producing types of CTX-M compared with those of 19 isolates producing different types of extended-spectrum beta-lactamases (ESBLs) in a well-defined North American population. Most CTX-M-14 producers (97%) were from phylogenic group D; 67% of the CTX-M-15 producers were from group B2. A single CTX-M-14-producing strain belonged to clonal group A. There were significant prevalence differences for individual virulence factors among CTX-M producers and nonproducers; however, aggregate virulence factor scores were similar. CTX-M producers more commonly caused repeat urinary tract infections. Our results indicate that CTX-M type predicts phylogenetic background, and the virulence potential of ESBL-producing E. coli isolates is a complex issue, requiring further study and ongoing surveillance.

Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) typically cause nosocomial infections. Previous surveillance in the Calgary Health Region showed that Escherichia coli strains producing ESBLs were common among community patients. During the period (2000 to 2002): 23 of 157 (15%) of the strains were positive for blaCTX-M genes from the CTX-M-I group (CTX-M-1-like) and 87 of 157 (55%) of the strains were positive for blaCTX-M genes from the CTX-M-III group (CTX-M-14-like). The objective of this study was to investigate the molecular epidemiology of these strains. The beta-lactamases were characterized, and the genetic relatedness of the isolates was analyzed by digesting genomic DNA with the restriction endonuclease XbaI and by performing pulse-field gel electrophoresis (PFGE). PFGE revealed two closely related restriction patterns (clusters CTXM14A and CTXM14AR) among 67 (77%) CTX-M-14 producers. These strains from CTXM14A had nearly identical susceptibility patterns and were isolated most often from urine samples obtained at community sites during 2000 and 2001. Strains from the CTX-M-1-like and CTX-M-negative groups were unrelated to clusters CTXM14, CTXM14AR, and CTXM14NR. We conclude that clonally related strains of E. coli producing CTX-M-14 beta-lactamases were responsible for a predominantly community-wide outbreak. Further studies are warranted to investigate whether community-onset diseases caused by ESBL-producing E. coli are related to a point source or transmission within the community.

A prospective, population-based laboratory surveillance study was conducted to define the epidemiology of extended-spectrum beta -lactamase-producing Escherichia coli infections in the Calgary Health Region during the years 2000-2002. The incidence was 5.5 cases per 100,000 population per year. The annualized incidence of 3.9 cases per 100,000 population for January through March was significantly lower than the incidence for the other quarters of the year (6.0 per 100,000 population; P<.01). Seventy-one percent of subjects had community-onset disease. Patients aged > or =65 years (22.0 vs. 3.8 cases per 100,000 population per year; P<.0001) and women (9.2 vs. 1.7 cases per 100,000 population per year; P<.0001) had significantly higher rates of infection. Polymerase chain reaction identified 23 (15%) of 157 isolates as positive for blaCTX-M genes from the CTX-M-I subgroup and 87 (55%) from the CTX-M-III subgroup. Ciprofloxacin resistance was independently associated with CTX-M- beta -lactamases (odds ratio, 14.2; 95% confidence interval, 3.69-54.84). Strains of E. coli with blaCTX-M genes commonly cause community-onset infections, and women and older patients are at highest risk.

Background: Prompt administration of adequate empiric antimicrobial therapy is a major determinant influencing the outcome of serious infections. The objective of this study was to describe empiric antimicrobial therapy employed and assess its effect on the outcome of patients bacteremic with extended-spectrum beta-lactamase (ESBL) producing Escherichia coli and Klebsiella pneumoniae. Findings: A retrospective surveillance study of all patients with bacteremias caused by ESBL-producing E. coli and K. pneumoniae (EK-ESBL) from 2000-2007 in the Calgary Health Region was conducted. Data were available for 79 episodes of bacteremia among 76 patients. Forty-four (56%) were male, the median age was 70.0 yrs [interquartile range (IQR) 60.6-70.1 yrs], and 72 (91%) episodes were E. coli. Seventy-four episodes (94%) were treated with empiric therapy within the first 48 hours. A non-statistically significant increased mortality occurred in those treated empirically with a beta-lactam/beta-lactamase inhibitor combination (6/16; 38% vs. 10/53; 18%; p = 0.063) while empiric carbapenem therapy was associated with lower mortality (0/10 died vs. 16/53 (30%), p = 0.089). Only 42 (53%) episodes received adequate therapy within the first 48 hours. The median time to first adequate antibiotic therapy was 41.0 hours [IQR 5.8-59.5] (n = 75). The case-fatality rate was not different among those that received adequate compared to inadequate therapy by 48 hours as compared to inadequate empiric therapy (9/42; 21% vs. 7/37; 19%; p = 1.0). Conclusion: Inadequate empiric therapy is common among patients with EK-ESBL bacteremia in our region but was not associated with adverse mortality outcome. [ABSTRACT FROM AUTHOR]

Summary: Objectives: Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli have emerged as significant causes of community-onset disease. We sought to identify risk factors for acquiring community-onset ESBL-producing E. coli. Methods: Prospective, population-based surveillance for ESBL-producing E. coli was performed in the Calgary Health Region (population 1.2 million), Canada during a two-year period. Results: 247 patients were identified; 177 (72%; 7.6 per 100,000/year) were community acquired, and 70 (28%; 3.0 per 100,000/year) were healthcare associated. The acquisition risk increased with advancing age. Females were at higher risk as compared to males [relative risk (RR) 4.3; 95% confidence interval (CI), 3.1–6.1] as were urban as compared to rural residents (RR 2.2; 95% CI, 1.4–3.6). A number of co-morbidities increased risk (RR; 95% CI) including requirement for hemodialysis (56.3; 15.1–147.4), urinary incontinence (21.7; 15.0–30.9), cancer (11.1; 7.0–17.0), heart disease (6.5; 4.3–9.7), and diabetes (4.4; 2.6–7.1). Overseas travel overall increased the risk (5.7; 4.1–7.8) and was highest in travelers to India (145.6; 77.7–252.1), the Middle East (18.1; 8.1–35.2), and Africa (7.7; 2.8–17.2). Conclusions: Advancing age, female gender, co-morbid medical conditions, and foreign travel are important risk factors for developing community-onset ESBL-producing E. coli infections in our region. Emergence of anti-microbial-resistant pathogens is a global concern. [Copyright &y& Elsevier]

In the Calgary Health Region during 2000-2003, prospective, active, population-based laboratory surveillance for all cefoxitin-resistant Escherichia coli isolates was performed. Isolates were screened with an inhibitor-based disk test, and plasmid-mediated types were identified by multiplex PCR with sequencing. A total of 369 AmpC β-lactamase--producing E. coli isolates were identified; annual incidence rates were 1.7, 4.3, 11.2, and 15 per 100,000 residents for each year, respectively. AmpC β-lactamase-producing E. coli was 5x more likely to be isolated from female than male patients across all age groups except <1 year. Of these isolates, 83% were community onset, and urine was the principal site of isolation (90% of patients). PCR showed that 125 (34%) were positive for blacmy genes; sequencing identified these enzymes to be CMY-2. In this large Canadian region, AmpC β-lactamase--producing E. coli is an emerging community pathogen that commonly causes urinary tract infections in older women. [ABSTRACT FROM AUTHOR]

Background: Blood cultures are a gold standard specific test for diagnosing many infections. However, the low yield may limit their usefulness, particularly in low-risk populations. This study was conducted to assess the utility of blood cultures drawn from ambulatory outpatients. Methods: Blood cultures drawn at community-based collection sites in the Calgary Health Region (population 1 million) in 2001 and 2002 were included in this study. These patients were analyzed by linkages to acute care health care databases for utilization of acute care facilities within 2 weeks of blood culture draw. Results: 3102 sets of cultures were drawn from 1732 ambulatory outpatients (annual rate = 89.4 per 100,000 population). Significant isolates were identified from 73 (2.4%) sets of cultures from 51 patients, including Escherichia coli in 18 (35%) and seven (14%) each of Staphylococcus aureus and Streptococcus pneumoniae. Compared to patients with negative cultures, those with positive cultures were older (mean 49.6 vs. 40.1 years, p < 0.01), and more likely to subsequently receive care at a regional emergency department, outpatient antibiotic clinic, or hospital (35/51 vs. 296/ 1681, p < 0.0001). Of the 331 (19%) patients who received acute care treatment, those with positive cultures presented sooner after community culture draw (median 2 vs. 3 days, p < 0.01) and had longer median treatment duration (6 vs. 2 days, p < 0.01). Conclusion: Blood cultures drawn in outpatient settings are uncommonly positive, but may define patients for increased intensity of therapy. Strategies to reduce utilization without excluding patients with positive cultures need to be developed for this patient population. [ABSTRACT FROM AUTHOR]

This study aimed to compare antimicrobial resistance (AMR) in extended-spectrum cephalosporin-resistant and generic Escherichia coli from a One Health continuum of the beef production system in Alberta, Canada. A total of 705 extended-spectrum cephalosporin-resistant E. coli (ESCr) were obtained from: cattle feces (CFeces, n = 382), catch basins (CBasins, n = 137), surrounding streams (SStreams, n = 59), beef processing plants (BProcessing, n = 4), municipal sewage (MSewage; n = 98) and human clinical specimens (CHumans, n = 25). Generic isolates (663) included: CFeces (n = 142), CBasins (n = 185), SStreams (n = 81), BProcessing (n = 159) and MSewage (n = 96). All isolates were screened for antimicrobial susceptibility to 9 antimicrobials and two clavulanic acid combinations. In ESCr, oxytetracycline (87.7%), ampicillin (84.4%) and streptomycin (73.8%) resistance phenotypes were the most common, with source influencing AMR prevalence (p < 0.001). In generic E. coli, oxytetracycline (51.1%), streptomycin (22.6%), ampicillin (22.5%) and sulfisoxazole (14.3%) resistance were most common. Overall, 88.8% of ESCr, and 26.7% of generic isolates exhibited multi-drug resistance (MDR). MDR in ESCr was high from all sources: CFeces (97.1%), MSewage (96.9%), CHumans (96%), BProcessing (100%), CBasins (70.5%) and SStreams (61.4%). MDR in generic E. coli was lower with CFeces (45.1%), CBasins (34.6%), SStreams (23.5%), MSewage (13.6%) and BProcessing (10.7%). ESBL phenotypes were confirmed in 24.7% (n = 174) ESCr and 0.6% of generic E. coli. Prevalence of bla genes in ESCr were blaCTXM (30.1%), blaCTXM-1 (21.6%), blaTEM (20%), blaCTXM-9 (7.9%), blaOXA (3.0%), blaCTXM-2 (6.4%), blaSHV (1.4%) and AmpC β-lactamase blaCMY (81.3%). The lower AMR in ESCr from SStreams and BProcessing and higher AMR in CHumans and CFeces likely reflects antimicrobial use in these environments. Although MDR levels were higher in ESCr as compared to generic E. coli, AMR to the same antimicrobials ranked high in both ESCr and generic E. coli sub-populations. This suggests that both sub-populations reflect similar AMR trends and are equally useful for AMR surveillance. Considering that MDR ESCr MSewage isolates were obtained without enrichment, while those from CFeces were obtained with enrichment, MSewage may serve as a hot spot for MDR emergence and dissemination. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance (AMR) has important implications for the continued use of antibiotics to control infectious diseases in both beef cattle and humans. AMR along the One Health continuum of the beef production system is largely unknown. Here, whole genomes of presumptive extended-spectrum β-lactamase E. coli (ESBL-EC) from cattle feces (n = 40), feedlot catch basins (n = 42), surrounding streams (n = 21), a beef processing plant (n = 4), municipal sewage (n = 30), and clinical patients (n = 25) are described. ESBL-EC were isolated from ceftriaxone selective plates and subcultured on ampicillin selective plates. Agreement of genotype-phenotype prediction of AMR ranged from 93.2% for ampicillin to 100% for neomycin, trimethoprim/sulfamethoxazole, and enrofloxacin resistance. Overall, β-lactam (100%; blaEC, blaTEM-1, blaSHV, blaOXA, blaCTX-M-), tetracycline (90.1%; tet(A), tet(B)) and folate synthesis (sul2) antimicrobial resistance genes (ARGs) were most prevalent. The ARGs tet(C), tet(M), tet(32),blaCTX-M-1, blaCTX-M-14, blaOXA-1, dfrA18, dfrA19, catB3, and catB4 were exclusive to human sources, while blaTEM-150, blaSHV-11–12,dfrA12, cmlA1, and cmlA5 were exclusive to beef cattle sources. Frequently encountered virulence factors across all sources included adhesion and type II and III secretion systems, while IncFIB(AP001918) and IncFII plasmids were also common. Specificity and prevalence of ARGs between cattle-sourced and human-sourced presumptive ESBL-EC likely reflect differences in antimicrobial use in cattle and humans. Comparative genomics revealed phylogenetically distinct clusters for isolates from human vs. cattle sources, implying that human infections caused by ESBL-EC in this region might not originate from beef production sources. [ABSTRACT FROM AUTHOR]

Purpose: There are a number of biases that may influence the validity of laboratory-based surveillance for antimicrobial resistance. Our objective was to evaluate the potential magnitude of bias in reporting of etiologic agents and their resistance rates associated with inclusion of multiple patient samples and non-random timing and location of sampling. Methods: All urine cultures submitted to a regional laboratory in the Calgary Health Region during 2004 and 2005 were studied. Comparisons were then made using either the overall cohort or different subgroups compared with the "reference" or gold standard population where only the first isolate per patient per year per species was included. Results: Overall 56,897 organisms were cultured at ≤104 cfu/mL from 53,548 samples from 35,890 patients; 39,835 organisms were included in the reference cohort. Escherichia coli was reported in 37,246 (65.5%) of overall cohort and 28,257 (70.9%) of the reference cohort. Therefore, the overall cohort resulted in a relative underestimation of the importance of E. coli as the principal cause of urinary tract infections by 8%. Similarly, reported rates of resistance to antimicrobial agents most notably ciprofloxacin [6,480/ 52,544 (12.3%) vs. 2,647/37,086 (7.1%)], gentamicin [2,991/48,070 (6.2%) vs. 1,567/34,608 (4.5%)], and ceftriaxone [1,737/44,922 (3.9%) vs. 889/32,745 (2.7%)] were higher in the overall than in the reference cohorts. There were large differences in both the distribution of organisms and rates of resistance associated with sampling during different times of the day, week, and year as well as from acute care hospitals and outpatient clinics (P≤0.001). Conclusions: Reports from laboratory-based surveillance studies may be biased depending on the population studied and method of sampling employed. Care must be taken in interpreting results of surveillance studies that do not protect from these major sources of bias. [ABSTRACT FROM AUTHOR]