RESUMO
A study was carrried out to determine the predictive value and the cost-effectiveness of the indirect hemagglutination test using highly purified Vi antigen as a means of screening Salmonella Typhi carrriers in a high-risk group living in an área where typhoid fever is emdemic. The group consisted of women over age 30 who were participating in a municipal sanitary control program for food handlers in Lima, Perú. Test yielding an anti-Vi antibody titer= 1:40 were considered positive (79 percent sensitivity, and 99 percent and 100 percent specificity for the local population). On this basis, 29 women (1.5 percent) tested positive out of a total of 1 931. A follow-up bacteriological study demonstrated that 26 of these 29 women were carriers of S. typhi; thus, the test had a predictive value of 15 percent. The prevalence of carriers in this group was estimated at 292 per 100 000 population. The test cost $US 0.30 per person. In comparison, the method that requires a series of three fecal cultures to isolate the causative agent would have cost $US 1.72. It can be concluded that the test studied is suficiently sensitive, that it is highly specific, and that it is cost-effective when used to detect S. typhi carriers in áreas where typhoid fever is endemic