Estimation of symptomatic and asymptomatic Salmonella infections.

Since the surveillance of salmonellosis in Sweden is primarily passive, it can be assumed that most of the asymptomatic salmonella infections are never identified. We here report the proportion of asymptomatic and symptomatic salmonella infections in Swedish travellers to different geographic areas as well as in "contacts" to index cases with salmonellosis. In the 346 travellers studied Salmonellae were isolated equally often among those who remained healthy (10/216; 4.6%) as in those with intestinal symptoms (7/130; 5.4%). Similarly, most of the salmonella-infected "contacts" to index cases (11/15; 73%) had an asymptomatic infection. No difference in the mean duration of excreting Salmonella in the stool was found between carriers with symptomatic and asymptomatic infection. The literature concerning transmission of nontyphi Salmonellae from carriers was reviewed. Since person to person transmission is rarely noted, screening for carriers may be limited to food handlers and hospital personnel taking care of patients susceptible to low infective doses of Salmonella. Similarly, follow-up faecal cultures in individuals with notified salmonella infection may be restricted to these groups.