Sero-epidemiology as a tool to study the incidence of Salmonella infections in humans.

Although most foodborne infections are undiagnosed, the incidence of these infections is usually calculated from reported cases. We present a novel population-based method to estimate the incidence of non-typhoid Salmonella infections. From 154 patients with confirmed Salmonella serotype Enteritidis infection, we determined the kinetics of the antibody response. The estimated mean responses for the three classes of serum antibodies were combined such that the time from infection could be estimated from antibody measurements. Next, serum samples collected in 1983, 1986, 1992, and 1999 from the general population were analysed for antibodies. We demonstrated how these measurements can be translated into an estimate of the general incidence. Based on serology markers there were 13 exposures leading to seroresponse of Salmonella Enteritidis/1000 person-years in 1983; the similar number in 1999 was 217. This trend confirms the increase in the number of culture-confirmed cases reported to the national surveillance system.