Daniel B. Gregson

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.

Population-based study of the epidemiology of and the risk factors for pyogenic liver abscess.

BACKGROUND & AIMSnPyogenic liver abscess (PLA) is relatively uncommon in North America but is associated with significant morbidity and mortality. Our objective was to characterize the incidence of, risk factors for, and outcomes of PLA in a nonselected population.nnnMETHODSnPopulation-based surveillance was conducted in the Calgary Health Region (CHR) between April 1, 1999 and March 31, 2003. All adult CHR residents with PLA were identified, and charts were reviewed.nnnRESULTSnSeventy-one CHR residents developed a PLA for an annual incidence of 2.3 per 100,000 population. There was an increasing incidence of PLA with advancing age. Men were at much higher risk of acquiring a PLA as compared to women (3.3 vs 1.3 per 100,000; relative risk [RR], 2.6; 95% confidence interval [CI], 1.5-4.6; P < .001), and this was observed across all age groups. A number of comorbid conditions were associated with significantly higher risk for developing a PLA including liver transplantation patients (RR, 444.8; 95% CI, 89.5-1356.0; P < .0001), diabetics (RR, 11.1; 95% CI, 6.3-19; P < .0001), and patients with a history of malignancy (RR, 13.3; 95% CI, 6.9-24.4; P < .0001). No other solid organ transplantation patient was at increased risk. All patients required admission to hospital (median length of stay, 16 days), and 7 (10%) patients died in hospital, corresponding to a mortality rate of 0.22 per 100,000 population.nnnCONCLUSIONSnThis study provides important data on the burden of PLA and identifies risk groups that might potentially benefit from preventive efforts.

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.

Population‐Based Epidemiological Study of Infections Caused by Carbapenem‐Resistant Pseudomonas aeruginosa in the Calgary Health Region: Importance of Metallo‐β‐Lactamase (MBL)–Producing Strains

BACKGROUNDnA study was conducted in the Calgary Health Region between May 2002 and April 2004 to define the population-based epidemiological characteristics of infections caused by imipenem-resistant Pseudomonas aeruginosa and to explore the clinical outcomes due to metallo- beta -lactamase (MBL)-producing and non-MBL-producing strains.nnnMETHODSnDetailed clinical information was obtained by chart review, and phenotypic and molecular characterizations were performed using the MBL E-test, polymerase chain reaction with sequencing, and pulsed-field gel electrophoresis.nnnRESULTSnA total of 228 patients with infections caused by imipenem-resistant P. aeruginosa were identified (annual incidence, 10.5 cases/100,000 population), with the highest incidence rate in those >or=75 years old. MBL-producing strains (98/228) were associated with higher rates of multidrug resistance and bacteremia. Ninety MBL-producing strains also produced VIM-2, 4 produced IMP-7, and 4 were unclassified. A cluster of VIM-2-producing strains was responsible for a nosocomial outbreak during 2003. The case-fatality rate was significantly higher for infections caused by MBL-producing strains than for those caused by non-MBL-producing strains (25% vs. 13%; relative risk, 1.98 [95% confidence interval, 1.00-3.90]; P=.05).nnnCONCLUSIONnMBL-producing P. aeruginosa strains were associated with a higher case-fatality rate and invasive disease. Our study highlights the potential importance of molecular laboratory techniques in infection control and patient care.

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.

The distinct category of healthcare associated bloodstream infections

BackgroundBloodstream infections (BSI) have been traditionally classified as either community acquired (CA) or hospital acquired (HA) in origin. However, a third category of healthcare-associated (HCA) community onset disease has been increasingly recognized. The objective of this study was to compare and contrast characteristics of HCA-BSI with CA-BSI and HA-BSI.MethodsAll first episodes of BSI occurring among adults admitted to hospitals in a large health region in Canada during 2000-2007 were identified from regional databases. Cases were classified using a series of validated algorithms into one of HA-BSI, HCA-BSI, or CA-BSI and compared on a number of epidemiologic, microbiologic, and outcome characteristics.ResultsA total of 7,712 patients were included; 2,132 (28%) had HA-BSI, 2,492 (32%) HCA-BSI, and 3,088 (40%) had CA-BSI. Patients with CA-BSI were significantly younger and less likely to have co-morbid medical illnesses than patients with HCA-BSI or HA-BSI (p < 0.001). The proportion of cases in males was higher for HA-BSI (60%; p < 0.001 vs. others) as compared to HCA-BSI or CA-BSI (52% and 54%; p = 0.13). The proportion of cases that had a poly-microbial etiology was significantly lower for CA-BSI (5.5%; p < 0.001) compared to both HA and HCA (8.6 vs. 8.3%). The median length of stay following BSI diagnosis 15 days for HA, 9 days for HCA, and 8 days for CA (p < 0.001). Overall the most common species causing bloodstream infection were Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. The distribution and relative rank of importance of these species varied according to classification of acquisition. Twenty eight day all cause case-fatality rates were 26%, 19%, and 10% for HA-BSI, HCA-BSI, and CA-BSI, respectively (p < 0.001).ConclusionHealthcare-associated community onset infections are distinctly different from CA and HA infections based on a number of epidemiologic, microbiologic, and outcome characteristics. This study adds further support for the classification of community onset BSI into separate CA and HCA categories.

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.

Long-term mortality associated with community-onset bloodstream infection

PurposeAlthough 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 (≤28xa0days) and late (>28xa0days) mortality and assess determinants of late death following community-onset bloodstream infection.MethodsAll 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.ResultsA 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 28xa0days, the median time to death was 4 (interquartile range [IQR] 1–12)xa0days, with 158 (28%) and 212 (38%) of early (≤28-day) deaths occurring by days 1 and 2, respectively. Among survivors to 28xa0days (nxa0=xa03,992), 570 (14%) suffered late 1-year mortality (i.e., death occurred between 29 and 365xa0days 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.ConclusionsCommunity-onset bloodstream infection is associated with major early and late mortality.

Epidemiology of Staphylococcus aureus nasal colonization and influence on outcome in the critically ill

PURPOSEnTo determine the rate of Staphylococcus aureus nasal colonization at admission to intensive care units (ICU) and assess its effect on the development of an ICU-acquired S aureus infection.nnnMATERIALS AND METHODSnWe screened all ICU admissions for nasal colonization within the Calgary Health Region from October 2005 to September 2006 and followed up patients to hospital discharge or death or S aureus infection to 30 days.nnnRESULTSnOne thousand three hundred eight patients were admitted to ICU for more than 48 hours and screened for nasal colonization. Fifty (4%) were methicillin-resistant S aureus (MRSA)-positive, 311 (24%) were methicillin-sensitive S aureus (MSSA)-positive, and 947 (72%) were nasal screen-negative. Overall, 5% (63/1239) of patients uninfected at ICU admission developed an ICU-acquired S aureus infection. The rate of ICU-acquired infection was 5% in MRSA colonized patients, 12% in MSSA colonized patients, and 3% in noncolonized patients. A positive nasal screen (odds ratio [OR], 4.7; 95% confidence interval [CI] 2.7-7.9), neuro/trauma patients (OR, 3.1; 95% CI, 1.8-5.2), and higher first Therapeutic Intervention Scoring System score (OR, 1.03 per point; 95% CI, 1.01-1.05) were independent predictors for developing an ICU-acquired S aureus infection.nnnCONCLUSIONSnNasal colonization with S aureus is a significant risk factor for ICU-acquired S aureus infections, and strategies to control these infections should target both MSSA and MRSA colonization.

Blood cultures in ambulatory outpatients.

BackgroundBlood 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.MethodsBlood 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.Results3102 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).ConclusionBlood 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.