T. Ross

Staphylococcus aureus Bloodstream Infections: Risk Factors, Outcomes, and the Influence of Methicillin Resistance in Calgary, Canada, 2000–2006

BACKGROUNDnReports have suggested that the epidemiological profile of invasive Staphylococcus aureus infections is changing. We sought to describe the epidemiological profile of S. aureus bacteremia and to assess whether the incidence and severity of and the antimicrobial resistance rates associated with this bacteremia are increasing.nnnMETHODSnPopulation-based surveillance for S. aureus bacteremias was conducted in the Calgary Health Region (population, 1.2 million) during 2000-2006.nnnRESULTSnThe annual incidence of S. aureus bacteremia was 19.7 cases/100,000 population. Although rates of health care-associated and nosocomial methicillin-susceptible S. aureus (MSSA) bacteremia were similar throughout the study, rates of community-acquired MSSA bacteremia gradually decreased, and rates of methicillin-resistant S. aureus (MRSA) bacteremia dramatically increased. The clonal type predominantly isolated was CMRSA-2 (i.e., Canadian [C] MRSA-2), but CMRSA-10 (USA300) strains have been increasingly isolated, especially from community-onset infections, since 2004. Dialysis dependence, organ transplantation, HIV infection, cancer, and diabetes were the most important risk factors and were comparable for MSSA and MRSA bacteremias. The overall case-fatality rate was higher among individuals with MRSA (39%) than among those with MSSA (24%; P< .0001). The annual overall population mortality rate associated with S. aureus bacteremia did not significantly change during the study.nnnCONCLUSIONSnAlthough the overall influence of S. aureus bacteremia has not significantly changed, MRSA has emerged as an important etiology in our region.

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.

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 ~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, 5.8–6.15; 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.

Burden of community-onset bloodstream infection: a population-based assessment

Although community-onset bloodstream infection (BSI) is recognized to be a major cause of morbidity and mortality, there is a paucity of population-based studies defining its overall burden. We conducted population-based laboratory surveillance for all community-onset BSI in the Calgary Health Region during 2000-2004. A total of 4467 episodes of community-onset BSI were identified for an overall annual incidence of 81.6/100,000. The three species, Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae were responsible for the majority of community-onset BSI; they occurred at annual rates of 25.8, 13.5, and 10.1/100,000, respectively. Overall 3445/4467 (77%) episodes resulted in hospital admission representing 0.7% of all admissions to major acute care hospitals. The subsequent hospital length of stay was a median of 9 (interquartile range, 5-15) days; the total days of acute hospitalization attributable to community-onset BSI was 51,146 days or 934 days/100,000 annually. Four hundred and sixty patients died in hospital for a case-fatality rate of 13%. Community-onset BSI is common and has a major patient and societal impact. These data support further efforts to reduce the burden of community-onset BSI.

Epidemiology of Clostridium species bacteremia in Calgary, Canada, 2000–2006

OBJECTIVESnTo define the incidence, risk factors for acquisition, and outcomes associated with clostridial bacteremia in a large Canadian health region.nnnMETHODSnRetrospective population-based surveillance for clostridial bacteremia was conducted among all residents of the Calgary Health Region (population 1.2 million) during 2000-2006.nnnRESULTSnOne 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 Crohns 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.nnnCONCLUSIONSnClostridium species bacteremia is associated with a significant burden of illness and hemodialysis and cancer patients are at highest risk.

Population-Based Study of the Epidemiology and the Risk Factors for Pseudomonas aeruginosa Bloodstream Infection

Background:Detailed population-based data on the epidemiologyof Pseudomonas aeruginosa bloodstream infectionsare sparse. We sought to describe the incidence rate, riskfactors, and outcomes associated with P. aeruginosa bacteremiain a large Canadian health region.Patients and Methods:A retrospective population-basedsurveillance for P. aeruginosa bacteremia was conductedin the Calgary Health Region (CHR, population:approx. 1.2 million) during the period from 2000 to2006.Results:A total of 284 incident cases of P. aeruginosabacteremia were identified in CHR residents, correspondingto 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 tothe general population, risk factors for bloodstreaminfection included male sex, increasing age, hemodialysis,solid organ transplant, diagnosis of cancer, heartdisease, HIV infection, diabetes mellitus, and/or chronicobstructive airway disease (COPD). Overall mortality was29%. Factors associated with mortality in univariateanalysis included pulmonary focus of infection andco-morbidities, including chronic liver disease, substanceabuse, heart disease, COPD, and cancer, and increasedwith the burden of co-morbidities. Despite thosepatients with CA disease having fewer co-morbidities,they had a significantly higher mortality rate thaneither healthcare-associated cases or nosocomial cases(RR 1.88, p = 0.05).Conclusions:This study documents that P. aeruginosabacteremic disease is responsible for a significant burdenof illness in general populations and identifies thosegroups at increased risk of infection and subsequentmortality. This information can be used to identify thoseindividuals likely to benefit from empiric anti-pseudomonaltherapies.

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.

Population-based laboratory surveillance of Hafnia alvei isolates in a large Canadian health region.

BackgroundHospital-based series have characterized Hafnia alvei primarily as an infrequent agent of polymicrobial nosocomial infections in males with underlying illness.MethodsWe conducted population-based laboratory surveillance in the Calgary Health Region during 2000–2005 to define the incidence, demographic risk factors for acquisition, and anti-microbial susceptibilities of Hafnia alvei isolates.ResultsA total of 138 patients with Hafnia alvei isolates were identified (2.1/100,000/year) and two-thirds were of community onset. Older age and female gender were important risk factors for acquisition. The most common focus of isolation was urine in 112 (81%), followed by lower respiratory tract in 10 (7%), and soft tissue in 5 (4%), and the majority (94; 68%) were mono-microbial. Most isolates were resistant to ampicillin (111;80%), cephalothin (106; 77%), amoxicillin/clavulanate (98; 71%), and cefazolin (95; 69%) but none to imipenem or ciprofloxacin.ConclusionHafnia alvei was most commonly isolated as a mono-microbial etiology from the urinary tract in women from the community. This study highlights the importance of population-based studies in accurately defining the epidemiology of an infectious disease.

Clinical and microbiological characteristics of bloodstream infections due to AmpC β-lactamase producing Enterobacteriaceae: an active surveillance cohort in a large centralized Canadian region.

BackgroundThe objective of this study was to describe the clinical and microbiological characteristics of bloodstream infections (BSIs) due to AmpC producing Enterobacteriaceae (AE) in a large centralized Canadian region over a 9-year period.MethodsAn active surveillance cohort design in Calgary, Canada.ResultsA cohort of 458 episodes of BSIs caused by AE was assembled for analysis. The majority of infections were of nosocomial origin with unknown sources. Enterobacter spp. was the most common species while BSIs due to Serratia spp. had a significant higher mortality when compared to other AE. Delays in empiric or definitive antibiotic therapy were not associated with a difference in outcome. However, patients that did not receive any empiric antimicrobial therapy had increased mortality (3/5; 60% vs. 57/453; 13%; pu2009=u20090.018) as did those that did not receive definitive therapy (6/17; 35% vs. 54/441; 12%; pu2009=u20090.015).ConclusionsDelays in therapy were not associated with adverse outcomes although lack of active therapy was associated with increased mortality. A strategy for BSIs due to AE where β-lactam antibiotics (including oxyimino-cephalosporins) are used initially followed by a switch to non-β-lactam antibiotics once susceptibility results are available is effective.