Potential risk factors for sporadic verocytotoxin-producing Escherichia coli (VTEC) infection in
Belgium were investigated in a matched case-control study. Thirty-seven cases, 8 infected with
O157 VTEC strains (all eaeA-positive), 29 with non-O157 VTEC strains (13 eaeA-positive and
16 eaeA-negative) and 69 matched controls were interviewed. In a conditional logistic
regression analysis, consumption of fish appeared to be a risk factor for infection (adjusted
odds ratio (OR) 3·25, P=0·04). Contact with dogs
(OR 0·27, P=0·04) and consumption of
shellfish (OR 0·19, P=0·05) showed a negative association, corresponding to a decrease in risk.
These findings might be explained if low level environmental exposure to VTEC induces
protective immunity. Eating raw meat, a frequent habit in Belgium, or hamburgers, or eating
in a fast-food restaurant was not more frequently reported by cases than controls. The
exposures causing sporadic infections with VTEC, in particular non-O157 strains, may be very
different from those which led to outbreaks, and may account for more cases overall.