Epidemiology and impact of methicillin-sensitive Staphylococcus aureus with ß-lactam antibiotic inoculum effects in adults with cystic fibrosis.

Staphylococcus aureus is the most prevalent cystic fibrosis (CF) pathogen. Several phenotypes are associated with worsened CF clinical outcomes including methicillin-resistance and small-colony-variants. The inoculum effect (IE) is characterized by reduced ß-lactam susceptibility when assessed at high inoculum. The IE associates with worse outcomes in bacteremia and other high-density infections, and may therefore be relevant to CF. The prevalence of IE amongst a CF cohort (age ≥18 years), followed from 2013 to 2016, was investigated. Yearly methicillin-sensitive S. aureus (MSSA) isolates were screened at standard (5 × 105 CFU/mL) and high (5 × 107 CFU/mL) inoculum against narrow-spectrum anti-Staphylococcal ß-lactams and those with anti-pseudomonal activity common to CF. A ≥ 4-fold increase in minimum inhibitory concentration between standard and high inoculum defined IE. Isolates underwent blaZ sequencing and genotyping and were compared against published genomes. Fifty-six percent (99/177) of individuals had MSSA infection. MSSA was observed at ≥105 CFU/mL in 44.8% of entry sputum samples. The prevalence of the IE was 25.0%-cefazolin; 13.5%-cloxacillin; 0%-meropenem; 1.0%-cefepime; 5.2%-ceftazidime; and 34.4%-piperacillin-tazobactam amongst baseline MSSA isolates assessed. blaZ A associated with cefazolin IE (P = 0.0011), whereas blaZ C associated with piperacillin-tazobactam IE (P < 0.0001). Baseline demographics did not reveal specific risk factors for IE-associated infections, nor were long-term outcomes different. Herein, we observed the IE in CF-derived MSSA disproportionally for cefazolin and piperacillin-tazobactam and this phenotype strongly associated with underlying blaZ genotype. The confirmation of CF being a high density infection, and the identification of high prevalence of MSSA with IE in CF supports the need for prospective pulmonary exacerbation treatment studies to understand the impact of this phenotype.

Multi-year comparison of VITEK® MS and 16S rRNA gene sequencing performance for the identification of rarely encountered anaerobes causing invasive human infections in a large Canadian region: can our laboratory abandon 16S rRNA gene sequencing?

BACKGROUND: Our large regional laboratory routinely provides a definitive identification (ID) for 800-1,200 anaerobic bacteria per annum that cause invasive human infections. An increasing number of isolates (i.e., 10 to 13%) recovered from clinical specimens from these cases were more unusual or rarely isolated genera and/or species (i.e., ≤5 individual cases/annum). METHODS: VITEK® MS (MALDI-TOF MS) is done initially on all anaerobic bacteria, but rare isolates undergo in-house PCR/sequencing when proteomics provides a wrong ID or no results despite repeat testing. A clinical microbiologist in consultation with the Infectious Diseases service approves molecular analyses. This multi-year comparison (2014-19) of the performance of MALDI-TOF MS and 16S rRNA gene sequencing using the IDNS® SmartGene bacterial dataset shows both method's abilities to provide a genus-level and/or species-level ID for rare isolates. RESULTS: 489 rare anaerobes were recovered from a variety of clinical specimens: 57% blood cultures, 19% other sterile fluids, 14% sterile tissues, 8% deep wounds/abscesses, and 2% prosthetic implants. 16S rRNA gene sequencing gave an accurate genus-vs. species level ID for 487/489 (99.6%) and 401/489 (82.0%) of isolates respectively. Accurate genus-vs species-level ID were obtained by MALDI-TOF MS for 269/489 (53.4%) and 187/489 (37.3%) of isolates respectively. MALDI-TOF MS gave wrong or no results for 35.1% of Gram-negative anaerobic cocci (GNAC), 62% of Gram-negative anaerobic bacilli (GNAB), 30.8% of Gram-positive anaerobic cocci (GPAC) and 46.3% of Gram-positive anaerobic bacilli (GPAB). Neither method gave an ID for one GNAB and one GPAC isolate. MALDI-TOF MS genus-level ID of GNAC and genus/species-level ID of GPAB improved during the study but its performance remained stable for genus- or species-level ID of other organism groups. CONCLUSIONS: MALDI-TOF MS provides accurate ID for most common anaerobes, but molecular analyses need to be available for rare isolates. Large complex laboratories should have a workflow for sending rare isolates for 16S rRNA gene sequencing in invasive cases where a definitive ID is clinically required.

Remote transient Lactobacillus animalis bacteremia causing prosthetic hip joint infection: a case report.

BACKGROUND: Lactobacillus spp. are uncommon pathogens in immunocompetent hosts, and even rarer causes of prosthetic device infections. CASE PRESENTATION: A case of chronic hip prosthetic joint infection (PJI) caused by L. animalis is described. This occurred 5 years after a transient bacteremia with the same organism. Whole genome sequencing of both isolates proved this PJI infection resulted from this remote bacteremia. CONCLUSIONS: We document that prosthetic joint infections may be a consequence of bacteremia as much as 3 years before the onset of symptoms.

Species-Level Identification of Actinomyces Isolates Causing Invasive Infections: Multiyear Comparison of Vitek MS (Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry) to Partial Sequencing of the 16S rRNA Gene.

Actinomyces species are uncommon but important causes of invasive infections. The ability of our regional clinical microbiology laboratory to report species-level identification of Actinomyces relied on molecular identification by partial sequencing of the 16S ribosomal gene prior to the implementation of the Vitek MS (matrix-assisted laser desorption ionization-time of flight mass spectrometry [MALDI-TOF MS]) system. We compared the use of the Vitek MS to that of 16S rRNA gene sequencing for reliable species-level identification of invasive infections caused by Actinomyces spp. because limited data had been published for this important genera. A total of 115 cases of Actinomyces spp., either alone or as part of a polymicrobial infection, were diagnosed between 2011 and 2014. Actinomyces spp. were considered the principal pathogen in bloodstream infections (n = 17, 15%), in skin and soft tissue abscesses (n = 25, 22%), and in pulmonary (n = 26, 23%), bone (n = 27, 23%), intraabdominal (n = 16, 14%), and central nervous system (n = 4, 3%) infections. Compared to sequencing and identification from the SmartGene Integrated Database Network System (IDNS), Vitek MS identified 47/115 (41%) isolates to the correct species and 10 (9%) isolates to the correct genus. However, the Vitek MS was unable to provide identification for 43 (37%) isolates while 15 (13%) had discordant results. Phylogenetic analyses of the 16S rRNA sequences demonstrate high diversity in recovered Actinomyces spp. and provide additional information to compare/confirm discordant identifications between MALDI-TOF and 16S rRNA gene sequences. This study highlights the diversity of clinically relevant Actinomyces spp. and provides an important typing comparison. Based on our analysis, 16S rRNA gene sequencing should be used to rapidly identify Actinomyces spp. until MALDI-TOF databases are optimized.

Development and Validation of a PCR Assay To Detect the Prairie Epidemic Strain of Pseudomonas aeruginosa from Patients with Cystic Fibrosis.

The monitoring of epidemic Pseudomonas aeruginosa is important for cystic fibrosis (CF) infection control. The prairie epidemic strain (PES) is common in western Canadian CF clinics. Using whole-genome sequencing, we identified a novel genomic island and developed a PCR assay for PES. Against a collection of 186 P. aeruginosa isolates, the assay had 98% sensitivity and 100% specificity.

Molecular Characterization by Using Next-Generation Sequencing of Plasmids Containing blaNDM-7 in Enterobacteriaceae from Calgary, Canada.

Enterobacteriaceae with blaNDM-7 are relatively uncommon and had previously been described in Europe, India, the United States, and Japan. This study describes the characteristics of Enterobacteriaceae (Klebsiella pneumoniae [n = 2], Escherichia coli [n = 2], Serratia marcescens [n = 1], and Enterobacter hormaechei [n = 1] isolates) with blaNDM-7 obtained from 4 patients from Calgary, Canada, from 2013 to 2014. The 46,161-bp IncX3 plasmids with blaNDM-7 are highly similar to other blaNDM-harboring IncX3 plasmids and, interestingly, showed identical structures within the different isolates. This finding may indicate horizontal transmission within our health region, or it may indicate contact with individuals from areas of endemicity within the hospital setting. Patients infected or colonized with bacteria containing blaNDM-7 IncX3 plasmids generate infection control challenges. Epidemiological and molecular studies are required to better understand the dynamics of transmission, the risk factors, and the reservoirs for bacteria harboring blaNDM-7. To the best of our knowledge, this is the first report of S. marcescens and E. hormaechei with blaNDM-7.

Incidence, risk factors, and outcomes for Enterococcus spp. blood stream infections: a population-based study.

BACKGROUND: Enterococci are a clinically significant cause of bloodstream infections (BSI), particularly in the nosocomial setting. The purpose of this study was to characterize the incidence, risk factors for acquisition, microbiological characteristics and mortality of enterococcal BSI within the well-defined population of a large Canadian health region. METHODS: Surveillance for all episodes of enterococcal BSI occurring among residents of the Calgary Health Zone (population 1.2 million) between 2000 and 2008 was conducted using an electronic surveillance system. Clinical features, microbiology, and outcomes were obtained. RESULTS: A total of 710 incident episodes of enterococcal BSI were identified for an annual incidence of 6.9 episodes per 100,000; the incidences of E. faecalis and E. faecium BSI were 4.5, and 1.6 per 100,000, respectively. Enterococcus faecalis infections were associated with a urinary focus, genitourinary malignancy, and abnormal genitourinary anatomy. E. faecium infections were associated with a gastrointestinal focus. Resistance to ampicillin, vancomycin and ciprofloxacin was higher in E. faecium infection. The overall case fatality rate was 22.8%, and was higher for E. faecium infection. CONCLUSIONS: This is the second population-based study to assess the risk factors for enterococcal BSI and compare the characteristics of infection with E. faecalis and E. faecium. Results suggest that BSI with E. faecalis and E. faecium should be regarded as two clinically different entities with unique sets of risk factors and microbiologic characteristics.

Bloodstream infections due to Peptoniphilus spp.: report of 15 cases.

Peptoniphilus spp. are Gram-positive anaerobic cocci (GPAC) that were formerly classified in the genus Peptostreptococcus. This study describes 15 cases of Peptoniphilus spp. bloodstream infection (BSI) diagnosed from 2007 to 2011 using 16S rDNA sequencing in patients with pneumonia, pre-term delivery, soft tissue infection or colon or bladder disease. Seven out of 15 (47%) of these cases had polymicrobial BSIs. One of the isolates was closely related to P. duerdenii (EU526290), while the other 14 isolates were most closely related to a Peptoniphilus sp. reference strain (ATCC 29743) and P. hareii (Y07839). Peptoniphilus is a rare but important cause of BSI.

Population-based assessment of the incidence, risk factors, and outcomes of anaerobic bloodstream infections.

BACKGROUND: Anaerobes are a relatively uncommon but important cause of bloodstream infection. However, their epidemiology has not been well defined in non-selected populations. We sought to describe the incidence of, risk factors for, and outcomes associated with anaerobic bacteremia. METHODS: Population-based surveillance for bacteremia with anaerobic microorganisms was conducted in the Calgary area (population 1.2 million) during the period from 2000 to 2008. RESULTS: A total of 904 incident cases were identified, for an overall population incidence of 8.7 per 100,000 per year; 231 (26 %) were nosocomial, 300 (33 %) were healthcare-associated community-onset, and 373 (41 %) were community-acquired. Elderly males were at the greatest risk. The most common pathogens identified were: Bacteroides fragilis group (3.6 per 100,000), Clostridium (non-perfringens) spp. (1.1 per 100,000), Peptostreptococcus spp. (0.9 per 100,000), and Clostridium perfringens (0.7 per 100,000). Non-susceptibility to metronidazole was 2 %, to clindamycin 17 %, and to penicillin 42 %. Relative to the general population, risk factors for anaerobic bloodstream infection included: male sex, increasing age, a prior diagnosis of cancer, chronic liver disease, heart disease, diabetes mellitus, stroke, inflammatory bowel disease, human immunodeficiency virus (HIV) infection, chronic obstructive pulmonary disease (COPD), and/or hemodialysis-dependent chronic renal failure (HDCRF). The 30-day mortality was 20 %. Increasing age, nosocomial acquisition, presence of malignancy, and several other co-morbid illnesses were independently associated with an increased risk of death. CONCLUSION: Anaerobic bloodstream infection is responsible for a significant burden of disease in general populations. The data herein establish the extent to which anaerobes contribute to morbidity and subsequent mortality. This information is key in developing preventative, empiric treatment and research priorities.

Population-based laboratory assessment of the burden of community-onset bloodstream infection in Victoria, Canada.

Although community-onset bloodstream infection (BSI) is recognized as a major cause of morbidity and mortality, its epidemiology has not been well defined in non-selected populations. We conducted population-based laboratory surveillance in the Victoria area, Canada during 1998-2005 in order to determine the burden associated with community-onset BSI. A total of 2785 episodes were identified for an overall annual incidence of 101·2/100,000. Males and the very young and the elderly were at highest risk. Overall 1980 (71%) episodes resulted in hospital admission for a median length of stay of 8 days; the total days of acute hospitalization associated with community-onset BSI was 28 442 days or 1034 days/100,000 population per year. The in-hospital case-fatality rate was 13%. Community-onset BSI is associated with a major burden of illness. These data support ongoing and future preventative and research efforts aimed at reducing the major impact of these infections.

Risk factors for recurrence and death after bacteraemia: a population-based study.

Although most bacteraemic outcome studies have focused on mortality, a repeated episode(s) is another important outcome of bacteraemia. We sought to characterize patient factors and microbial species associated with recurrence and death from bacteraemia. Population-based surveillance for bacteraemia was conducted in a Canadian health region during 2000-2008. Episodes of bacteraemia were extracted and characterized. Transition intensities of both recurrence and death were estimated by separate multivariate Cox proportional hazards models. We identified 9713 patients with incident episodes of bacteraemia. Within 1 year: 892 (9.2%) had recurrent bacteraemia, 2401 (24.7%) had died without a recurrent episode and 330 (3.4%) had died after a recurrent episode. Independent risk factors for recurrence within 1 year (hazard ratio; 95% confidence interval) were: increasing Charlson comorbidity scores (score 1-2: 2.2; 1.8-2.7 and score 3+: 3.4; 2.8-4.2), origin of infection (nosocomial: 2.1; 1.8-2.6 and healthcare-associated: 2.4; 2.0-2.8), microorganism (polymicrobial: 1.5; 1.2-2.0 and fungal: 2.8; 1.9-4.2) and focus of infection (verified urogenital: 0.4; 0.3-0.6). Independent risk factors for death within 1 year included: a recurrent bacteraemic episode 3.6 (3.1-4.0), increasing age and different foci of infection. This study identifies patient groups at risk of having a recurrent episode and dying from these infections. It adds recurrent bacteraemia as an independent risk factor of death within 1 year and may help to target patients for prevention or changes in management.

Long-term mortality associated with community-onset bloodstream infection.

PURPOSE: Although bloodstream infection is widely recognized as an important cause of acute morbidity and mortality, long-term mortality outcomes are less well defined. The objective of this study was to define the early (≤28 days) and late (>28 days) mortality and assess determinants of late death following community-onset bloodstream infection. METHODS: All adult residents of the Calgary Zone who had community-onset bloodstream infections during the period 1 January 2003 and 31 December 2007 were included. The mortality outcome was assessed through to 31 December 2008. RESULTS: A total of 4,553 cases were identified, of which 2,105 (46%) were healthcare-associated and 2,448 (54%) were community-acquired. The 28-day, 90-day, and 365-day all-cause case-fatality rates were 561/4,553 (12%), 780/4,553 (17%), and 1,131 (25%), respectively. Within the first 28 days, the median time to death was 4 (interquartile range [IQR] 1-12) days, with 158 (28%) and 212 (38%) of early (≤28-day) deaths occurring by days 1 and 2, respectively. Among survivors to 28 days (n = 3,992), 570 (14%) suffered late 1-year mortality (i.e., death occurred between 29 and 365 days postinception). The most common causes of death in this cohort as listed by the vital statistics data were malignancy in 220 (39%), cardiovascular in 135 (24%), and infection-related in 37 (7%). Older age, higher Charlson score, prolonged initial admission duration, and healthcare-associated and polymicrobial infections were independently associated with late 1-year mortality. CONCLUSIONS: Community-onset bloodstream infection is associated with major early and late mortality.

Identification by 16S rRNA gene sequencing of Negativicoccus succinicivorans recovered from the blood of a patient with hemochromatosis and pancreatitis.

We describe a case of Negativicoccus succinicivorans bacteremia in an adult man with hemochromatosis and acute pancreatitis. Conventional phenotypic tests and commercial identification systems failed to definitively identify the tiny anaerobic Gram-negative coccus isolated from two sets of blood cultures. The bacterium was identified by 16S rRNA gene sequencing and analysis using the SmartGene Integrated Database Network System software. This is the first published report of the recovery of this organism from a patient with invasive infection.

Population-based study of the epidemiology and the risk factors for Pseudomonas aeruginosa bloodstream infection.

BACKGROUND: Detailed population-based data on the epidemiology of Pseudomonas aeruginosa bloodstream infections are sparse. We sought to describe the incidence rate, risk factors, and outcomes associated with P. aeruginosa bacteremia in a large Canadian health region. PATIENTS AND METHODS: A retrospective population-based surveillance for P. aeruginosa bacteremia was conducted in the Calgary Health Region (CHR, population:approx. 1.2 million) during the period from 2000 to 2006. RESULTS: A total of 284 incident cases of P. aeruginosa bacteremia were identified in CHR residents, corresponding to an annual incidence rate of 3.6/100,000.Nosocomial acquisition accounted for 45% of cases,healthcare-associated community onset for 34% of cases,and community-acquired (CA) cases for 21%. Relative to the general population, risk factors for blood stream infection included male sex, increasing age, hemodialysis,solid organ transplant, diagnosis of cancer, heart disease, HIV infection, diabetes mellitus, and/or chronic obstructive airway disease (COPD). Overall mortality was 29%. Factors associated with mortality in univariate analysis included pulmonary focus of infection and co-morbidities, including chronic liver disease, substance abuse, heart disease, COPD, and cancer, and increased with the burden of co-morbidities. Despite those patients with CA disease having fewer co-morbidities,they had a significantly higher mortality rate than either healthcare-associated cases or nosocomial cases(RR 1.88, p = 0.05). CONCLUSIONS: This study documents that P. aeruginosa bacteremic disease is responsible for a significant burden of illness in general populations and identifies those groups at increased risk of infection and subsequent mortality. This information can be used to identify those individuals likely to benefit from empiric anti-pseudomonal therapies.

Detection of AmpC beta-lactamases in Escherichia coli, Klebsiella spp., Salmonella spp. and Proteus mirabilis in a regional clinical microbiology laboratory.

There are currently no standardized diagnostic tests available for the reliable detection of AmpC beta-lactamases in Klebsiella spp., Escherichia coli, Proteus mirabilis and Salmonella spp. A study was designed to evaluate a confirmation disk test using cefotetan (CTT) and cefoxitin (FOX) with phenylboronic acid (PBA). It also investigated the most suitable screening concentrations of FOX, ceftriaxone (CRO) and ceftazidime (CAZ) for the detection of AmpC beta-lactamases. A total of 126 control (consisting of 11 laboratory and 115 well-characterized clinical strains) and 29,840 non-repeat clinical isolates were included. FOX with PBA used in a confirmation test and CRO and CAZ as screening agents were found to be unreliable. FOX at >or= 32 mg/L was the best screening agent and CTT with PBA was the best confirmation test. Of the clinical isolates 635 (2%) were found to be resistant to cefoxitin (MIC >or= 32 ug/mL) and 332 (52%) were AmpC positive. E. coli was the most common organism with AmpC beta-lactamases and was mostly present in urines from community patients. It is recommended that laboratories use FOX at 32 mg/L as a screening agent and perform a disk test with CTT and PBA to confirm the presence of an AmpC cephalosporinase in isolates of Klebsiella spp., E. coli, Salmonella spp. and P. mirabilis. This approach is convenient, practical and easy to incorporate into the workflow of a clinical laboratory. False-positive AmpC detection may occur with KPC-producing bacteria when inhibitor-based methods are used.

Incidence, risk factors and outcomes of Escherichia coli bloodstream infections in a large Canadian region.

Although Escherichia coli is the most common cause of bloodstream infection, its epidemiology has not been well defined in non-selected populations. We sought to describe the incidence of risk factors for, and outcomes associated with, E. coli bacteraemia. Population-based surveillance for E. coli bacteraemia was conducted in the Calgary Health Region (population 1.2 million) during the period 2000-2006. In total, 2368 episodes of E. coli bacteraemia were identified for an overall annual population incidence of 30.3/100 000; 15% were nosocomial, 32% were healthcare-associated community-onset and 53% were community-acquired bacteraemias. The very young and the elderly were at highest risk for E. coli bacteraemia. Sixty per cent of the episodes occurred in females (relative risk 1.5; 95% CI 1.4-1.6). Dialysis, solid organ transplantation and neoplastic disease were the most important risk factors for acquiring E. coli bacteraemia. Rates of resistance to ampicillin, trimethoprim-sulphamethoxazole, gentamicin, ciprofloxacin, cefazolin and ceftriaxone increased significantly during the period 2000-2006. The case-fatality rate was 11% and the annual population mortality rate was 2.9/100 000. Increasing age, ciprofloxacin resistance, non-urinary focus and a number of comorbid illnesses were independently associated with an increased risk of death, and community acquisition and urinary focus were associated with a lower risk of death. This study documents the major burden of illness associated with E. coli bacteraemia and identifies groups at increased risk for acquiring and dying from these infections. The emergence of ciprofloxacin resistance and its adverse effect on patient outcome is a major concern.

Epidemiology of Clostridium species bacteremia in Calgary, Canada, 2000-2006.

OBJECTIVES: To define the incidence, risk factors for acquisition, and outcomes associated with clostridial bacteremia in a large Canadian health region. METHODS: Retrospective population-based surveillance for clostridial bacteremia was conducted among all residents of the Calgary Health Region (population 1.2 million) during 2000-2006. RESULTS: One hundred and thirty-eight residents had incident Clostridium species bacteremia (1.8 per 100,000/year); 45 (33%) were nosocomial, 55 (40%) were healthcare-associated community onset, and 38 (28%) were community acquired. Older age and a number of underlying conditions were risk factors for acquiring Clostridium species bacteremia most importantly hemodialysis [relative risk (RR) 212.3; 95% confidence interval (CI) 106.5-385.5], malignancy (RR 40.2; 95% CI 27.6-58.1), and Crohn's disease (RR 11.2; 95% CI 3.0-29.4). Clostridium perfringens was most commonly identified with 58 (42%) isolates followed by Clostridium septicum (19; 14%), Clostridium ramosum (13; 9%), Clostridium clostridiiforme (8; 6%), and Clostridium difficile (7; 5%). Reduced susceptibility to penicillin occurred in 14/135 (10%), to metronidazole in 2/135 (1%), and to clindamycin in 36/135 (27%) isolates. The median length of stay was 12.7 days and 39/130 (30%) patients died in hospital for mortality rate of 0.5 per 100,000/year. CONCLUSIONS: Clostridium species bacteremia is associated with a significant burden of illness and hemodialysis and cancer patients are at highest risk.

Population-based laboratory surveillance for Serratia species isolates in a large Canadian health region.

A population-based laboratory surveillance was conducted during a six-year period to define the incidence, demographic risk factors for acquisition, and anti-microbial susceptibilities of Serratia species isolates. A total of 715 incident Serratia species isolates were identified for an annual incidence of 10.8 per 100,000 residents; bacteremic disease occurred in 0.9 per 100,000 residents annually. The incidence increased with advancing age and males were at the highest risk. Ninety-two percent of the isolates were Serratia marcescens, and the majority (65%) of incident Serratia species isolates were of community onset. Ninety-five percent of isolates were susceptible to ciprofloxacin, 98% to gentamicin, 98% to trimethoprim/sulfamethoxazole, and >99% to imipenem. No yearly increase in resistance was observed. Serratia species isolation is most commonly of community onset and older patients and males are at increased risk. Despite reports of increasing resistance among Serratia species, the incidence in our region remains at a low stable rate.

Community-onset urinary tract infections: a population-based assessment.

BACKGROUND: Although multiple studies have investigated community-onset urinary tract infections (UTI), population-based data are lacking. We therefore conducted population-based laboratory surveillance in order to define the incidence, demographic risk factors, etiology, and antimicrobial susceptibilities of community onset UTI in a large Canadian region. METHODS: Laboratory surveillance for all community onset UTIs among residents of the Calgary Health Region (population approximately 1.2 million) was conducted during 2004/2005. Repeated positive samples within a 1-month period and those infections first cultured more than 2 days after admission to a hospital were excluded. RESULTS: A total of 40,618 episodes of community onset UTI occurred among 30,851 residents for an overall annual incidence of 17.5 per 1,000. Seventy-four percent of the cultures were submitted from ambulatory patients, 18% from hospitalized patients within the first 2 days of admission, and 9% from nursing home residents. Females were at significantly increased risk as compared to males (30.0 vs 5.0 per 1,000, RR 5.98; 95% CI, 5.81-6.15; p < 0.0001) as were the very young and very old. The most common infecting organisms were Escherichia coli (70%), Klebsiella pneumoniae (7%) and Enterococcus species (6%). Overall resistance rates among first isolates per patient tested were 14% for trimethoprim/sulfamethoxazole, 8% for cefazolin, 7% for nitrofurantoin, 6% for ciprofloxacin, 4% for gentamicin, and 2% for ceftriaxone although rates differed significantly based on sending location and patient age. CONCLUSION: This study provides novel information on the epidemiology of community-onset UTIs in a non-selected Canadian population. The occurrence, etiology, and resistance rates of community onset UTI differ significantly among definable population groups.