Risk factors for and prevention of sporadic infections with vero cytotoxin (shiga toxin) producing Escherichia coli O157

Abstract

Background: Recent outbreaks of vero cytotoxin (shiga toxin) producing Escherichia coli O157 (VTEC O157) infection have stimulated debate on food safety. However, 90% of cases in England and Wales are sporadic. We report a case-control study of sporadic VTEC O157 infection.

Methods: We compared 85 sporadic cases of VTEC O157 infection, identified through population surveillance, with 142 controls, randomly selected from general practitioners' lists. We matched cases and controls for age, sex, and family doctor's practice. Exposures to foods, water, animals, farms, and environmental factors were recorded. We visited the premises concerned when cases had eaten beefburgers or cooked sliced meats from caterers or had had contact with a farm.

Findings: Consumption of a beefburger from a catering premises other than from a fast-food chain A (a national chain) and consumption of cold cooked sliced meat (eg, in a salad or sandwich) from caterers, but not butchers, was associated with VTEC O157 infection (odds ratios 4.63 [95% CI 1.33-30.14] and 3.36 [1.04-12.74], respectively). Policies for ensuring thorough cooking of burgers by one national fast-food chain differed from the other catering premises we visited. There was evidence of person-to-person spread and transmission of VTEC O157 infection from animals.

Interpretation: Local inspection of catering establishments that serve cooked meats together with public education to prevent spread on farms and in houses would reduce the burden of VTEC O157 infection by about 10% for each risk factor.