A case-control study of Yersinia enterocolitica infections in Auckland

Objective: To identify major risk factors for Yersinia enterocolitica (YE) and identify measures to reduce YE infections. Methods: A prospective case control study, group age matched, using 186 cas es of YE identified by community pathology laboratories and 379 randomly se lected controls. Conducted between April 1995 and June 1996 in Auckland, Ne w Zealand. Face-to-face interviews used a standardised questionnaire examin ing exposures to factors potentially associated with YE infections includin g untreated water, unreticulated sewerage, consumption of selected foods, s elected food handling practices and sociodemographic factors. Multivariate logistic regression was used to calculate adjusted odds ratios for the pote ntial risk factors. Population attributable risk (PAR) was calculated for s ignificant exposures. Results: Having more than two people living in the home was more common amo ng cases than controls (OR=2.2). Town supply water (OR=0.2), reticulated se werage (OR=0.34) and looking after a young child (OR=0.51) were significant ly less common. Of the meats, only pork (OR=1.34) had a higher consumption rate, while bacon (OR=0.75) and smallgoods (OR=0.73) were consumed less fre quently by cases than controls. Eating food from a sandwich bar was more fr equent among cases (OR=1.18). Fruit and vegetable consumption was marginall y less (OR=0.98). The population attributable risk of these factors was 0.8 9, implying that 89% of YE would be eliminated if adverse exposures were re moved. Conclusions: The risk of YE illness is increased by contact with untreated water, unreticulated sewerage and consumption of pork. Investigation of non -town water supply, informal sewerage systems and methods of preparation an d consumption of pork are recommended to determine how YE enters the human food chain.