Risk Factors of Sporadic Human Infection of Shiga Toxin Producing Escherichia coli O157 and Non-O157 in Australia

Abstract

Background: Shiga toxin producing Escherichia coli (STEC) causes acute gastroenteritis characterised by abdominal cramps and bloody diarrhoea. In Australia and elsewhere, serotype O157 is the predominant strain of STEC. To investigate risk factors for STEC O157 and non-O157 infection we conducted an Australia-wide case control study between 2003 and 2007. Methods: Patients infected with STEC that were notified to health departments were eligible for the study and three controls per case were selected from a bank of controls based on sex and five year age groups. Cases were recruited in South Australia from July 2003, with all other Australian states participating from 2005. A standardised questionnaire was used to collect information regarding demographic data, food, behavioural and environmental exposures. All factors associated with O157 and non-O157 infection at the univariate level (p < 0.1) were included in separate logistic regression models. Results: The O157 analysis included 43 cases and 117 controls; the non-O157 analysis included 71 cases and 187 controls. In multivariate analysis, STEC O157 infection was associated with eating hamburgers (OR = 6.6, 95% CI = 2.2–20.0), eating out of the home (OR = 4.8, 95% CI = 1.7–13.6) and living on or visiting a farm (OR = 4.6, 95% CI = 1.2–17.6). Non-O157 STEC infection was associated with consuming chicken deli meat (OR = 5.3, 95% CI = 1.5–18.5), working with animals (OR = 3.2, 95% CI = 1.2-8.3) and asthma (OR = 2.7, 95% CI = 1.1–6.3). Bush camping in Australia had an elevated odds ratio, although this was not significant (OR = 3.3, 95% CI = 0.9–11.9). Conclusions: This national case control study is the first to provide risk factors for both O157 and non-O157 STEC cases. That O157 was associated with farm exposure and eating hamburgers is consistent with that reported internationally. However, some of the risk factors for non-0157 cases have not been reported previously. It is important to consider these risk factors in developing prevention programmes for this serious illness.