Objectives: To explain an increase in the incidence of salmonellosis caused by Salmonella agona in Israel between October 1994 and January 1995 in the light of an outbreak of S agona phage type 15 infection in England and Wales caused by consumption of a ready to eat savoury snack produced in Israel.
Design: Epidemiology of S agona in 1994-5 was analysed and two consecutive, case-control studies of 32 and 26 case-control pairs were performed. Phage typing and molecular methods were used to characterise strains of S agona isolated from cases and samples of the snack in Israel and England and Wales.
Results: The increase in the incidence of S agona between October 1994 and January 1995 was countrywide. Cases of infection with group B salmonella increased from 60% to 80% in children under 5 years old. In both case-control studies, cases consumed more of the snack than did controls (4.25 v 2.94 packets per week in the first study (P = 0.086) and 4.04 v 2.37 packets per week in the second study (P = 0.034)). When the two studies were combined there was a significant dose-response relation for the number of packets consumed weekly. Compared with consumption of less than two packets, the odds ratio was 1.43 for between two and six packets and 3.37 for seven or more packets (chi 2 for trend = 5.27, P = 0.02) S agona phage type 15 was isolated from a packet of the snack sold in Israel, and the strain was identical with those isolated from packets and cases in Israel and England and Wales.
Conclusions: This outbreak of S agona was caused by the contamination of a snack produced in Israel. Even under modern operating conditions, large, widespread international outbreaks of foodborne disease can occur. The success of this investigation resulted from excellent international collaboration between public health authorities.