Serological follow-up after non-typhoid salmonella infection in humans using a mixed lipopolysaccharide ELISA

In industrialized countries, non-typhoid salmonella are a frequent cause of bacterial gastroenteritis. Diagnosis is usually made by stool culture, which is labour-intensive and time-consuming. Sensitivity depends on handling of stool samples and delay from illness onset to sampling. We developed an indirect mixed enzyme-linked immunosorbent assay (ELISA) for the detection of human serum antibodies against lipopolysaccharide antigens of the two predominant serovars, Salmonella serovar Enteritidis (S. Enteritidis) and S. Typhimurium. We measured IgA, IgM and IgG in 964 sera from 302 patients with stool culture-confirmed acute salmonella gastroenteritis, in 300 sera from healthy blood donors, and in 147 sera from patients with antibodies against other bacteria. Patient sera were collected within 1 month and approximately 3, 6, and 12 months after illness onset. For sera collected ≤30 days of onset, sensitivity of the ELISA was 92% for S. Enteritidis and 86% for S. Typhimurium, with a specificity of 95% for both serovars. The mixed ELISA is a useful additional tool for the diagnosis of acute salmonella gastroenteritis. It allows rapid analysis of multiple samples, thus can be used for sero-epidemiological studies of large population-based serum collections in order to estimate the population incidence of salmonella infections. Another application is aetiological diagnostics in patients with suspected post-infectious complications such as reactive arthritis, even when faecal shedding of salmonella has ceased.