OUTBREAK OF SHIGELLA-SONNEI INFECTION TRACED TO IMPORTED ICEBERG LETTUCE

In the period from May through June 1994, an increase in the number of domestic Lases of Shigella sonnei infection was detected in several E uropean countries, including Norway, Sweden, and the United Kingdom. I n all three countries epidemiological evidence incriminated imported i ceberg lettuce of Spanish origin as the vehicle of transmission. The o utbreaks shared a number of common features: a predominance of adults among the case patients, the presence of double infections with other enteropathogens, and the finding of two dominant phage types among the bacterial isolates. In Norway 110 culture-confirmed cases of infectio n were recorded; more than two-thirds (73%) mere adults aged 30 to 60 years. A nationwide case-control study comprising 47 case patients and 155 matched control individuals showed that the consumption of import ed iceberg lettuce was independently associated viith an increased ris k of shigellosis. Epidemiological investigation of a local outbreak in criminated iceberg lettuce from Spain, consumed from a salad bar, as t he source. The presence of shigellae in the suspected food source coul d not be documented retrospectively. However, high numbers of fecal co liforms were detected in iceberg lettuce from patients' homes. Three l ettuce specimens yielded salmonellae. The imported iceberg lettuce har bored Escherichia coli strains showing resistance to several antimicro bial agents, including ampicillin, ciprofloxacin, gentamicin, and trim ethoprim-sulfamethoxazole. During the outbreak it is likely that thous ands of Norwegians and an unknown number of consumers in other countri es were exposed to coliforms containing antibiotic resistance genes.