A prospective case–control and molecular epidemiological study of human cases of Shiga toxin-producing Escherichia coli in New Zealand

Abstract

BackgroundShiga toxin-producing Escherichia coli (STEC) O157:H7 and related non-O157 STEC strains are enteric pathogens of public health concern worldwide, causing life-threatening diseases. Cattle are considered the principal hosts and have been shown to be a source of infection for both foodborne and environmental outbreaks in humans. The aims of this study were to investigate risk factors associated with sporadic STEC infections in humans in New Zealand and to provide epidemiological information about the source and exposure pathways.MethodsDuring a national prospective case–control study from July 2011 to July 2012, any confirmed case of STEC infection notified to regional public health units, together with a random selection of controls intended to be representative of the national demography, were interviewed for risk factor evaluation. Isolates from each case were genotyped using pulsed-field gel electrophoresis (PFGE) and Shiga toxin-encoding bacteriophage insertion (SBI) typing.ResultsQuestionnaire data from 113 eligible cases and 506 controls were analysed using multivariate logistic regression. Statistically significant animal and environmental risk factors for human STEC infections were identified, notably 'Cattle livestock present in meshblock’ (the smallest geographical unit) (odds ratio 1.89, 95% CI 1.04–3.42), 'Contact with animal manure’ (OR 2.09, 95% CI 1.12–3.90), and 'Contact with recreational waters’ (OR 2.95, 95% CI 1.30–6.70). No food-associated risk factors were identified as sources of STEC infection. E. coli O157:H7 caused 100/113 (88.5%) of clinical STEC infections in this study, and 97/100 isolates were available for molecular analysis. PFGE profiles of isolates revealed three distinctive clusters of genotypes, and these were strongly correlated with SBI type. The variable 'Island of residence’ (North or South Island of New Zealand) was significantly associated with PFGE genotype (p = 0.012).ConclusionsOur findings implicate environmental and animal contact, but not food, as significant exposure pathways for sporadic STEC infections in humans in New Zealand. Risk factors associated with beef and dairy cattle suggest that ruminants are the most important sources of STEC infection. Notably, outbreaks of STEC infections are rare in New Zealand and this further suggests that food is not a significant exposure pathway.

Geographic Divergence of Bovine and Human Shiga Toxin–ProducingEscherichia coliO157:H7 Genotypes, New Zealand1

“…The evidence of localized transmission of STEC between cattle and humans in New Zealand has advanced our understanding of the epidemiology of sporadic STEC infections in the country and is consistent with environmental- or animal-associated sources of infection rather than more disseminated foodborne outbreaks ( 20 ). Measures to prevent direct contact with animal fecal material in the environment include the wearing of protective clothing, increased hand washing, and targeted education of the population at risk regarding possible sources of STEC infection.…”

“…Bovine meat isolates were retrieved from carcass swab samples and bulk meat samples collected at beef-processing plants, so it could be hypothesized that fresh beef meat might be an exposure pathway for humans. However, although various food sources (including beef) were considered as potential risk factors during a nationwide prospective case-control study on sporadic STEC infections in humans, food was not identified as a major exposure pathway of infections in New Zealand ( 20 ). …”

Use of the EntericBio Gastro Panel II in a diagnostic microbiology laboratory: challenges and opportunities

“…3,11 In the 5 month study period, detection of VTEC increased by 325% compared with the previous 12 months of data for our region; the median age of patients was higher than that previously reported in NZ (16 years versus <5 years), and the proportion of non-O157 serotypes increased from <20% to 86%. 13,14 In common with other diagnostic laboratories in NZ, prior to the introduction of GP2, VTEC detection in our laboratory was limited to E. coli O157 and testing was performed on pre-selected groups of patients <6 years old and/or with possible haemolytic uraemic syndrome (HUS) noted on the request form. Only where request forms indicated HUS, but E. coli O157 was not isolated, were samples referred to the reference laboratory for stx gene testing.…”

<I>ESCHERICHIA COLI</I> PATHOTYPES ASSOCIATED WITH DIARRHEA IN HUMAN AND DOMESTIC ANIMALS

“…Transmission of E. coli O157:H7 to humans is principally via contamination of food by animal feces (Jaros et al, 2013). Food products of animal origin have been confirmed as vehicles of disease transmission in case-control studies of VTEC outbreaks and sporadic VTEC infections; these included raw milk (Guh et al, 2010) and undercooked meat products (Chapman et al, 2001).…”