EPIDEMIOLOGY OF SALMONELLA-TYPHIMURIUM O-4-12 INFECTION IN NORWAY - EVIDENCE OF TRANSMISSION FROM AN AVIAN WILDLIFE RESERVOIR

In 1987, a nationwide outbreak of Salmonella typhimurium 0:4-12 infect ion traced to contaminated chocolate bars occurred in Norway. In the 5 years after the outbreak, elevated numbers of sporadic cases caused b y the epidemic strain of Salmonella were detected, followed by a decli ne in subsequent years. To characterize the epidemiology of this infec tion, the authors analyzed information concerning all sporadic cases r eported in Norway from 1966 to 1996. Of the 153 patients infected by t he outbreak strain, 43% were less than 5 years of age, and only three persons had acquired the infection abroad. In contrast, 46% of the cas es attributable to other S. typhimurium 0:4-12 variants and 90% of the total number of Salmonella infections were related to foreign travel. A distinct seasonality was observed: 76% of the cases appeared betwee n January and April. At the same time of year, the epidemic strain was regularly encountered as the etiologic agent of fatal salmonellosis a mong wild passerine birds, suggesting an epidemiologic link between th e avian and human cases. The strain was rarely isolated from other sou rces. From 1990 to 1992, the authors conducted a prospective case-cont rol study of sporadic indigenous infections to identify risk factors a nd obtain guidance for preventive efforts. Forty-one case-patients, ea ch matched by age, sex, and geographic area with two population contro ls, were enrolled. In conditional logistic regression analysis, the fo llowing environmental factors were independently related to an increas ed risk of infection: drinking untreated water, having direct contact with wild birds or their droppings, and eating snow, sand, or soil. Ca ses were also more likely than controls to report having antecedent or concurrent medical disorders. Forty-six percent of the study patients were hospitalized for their salmonellosis.