Evaluation of community-based serologic screening for identification of chronic Salmonella Typhi carriers in Vietnam

Objectives: To determine the utility of screening anti-Vi antibodies to detect chronic Salmonella Typhi carriers in an endemic community. Methods: We conducted a community-based serologic survey for anti-Vi antibodies to identify chronic Salmonella Typhi carriers in a typhoid endemic region in Vietnam. Results: We tested sera from 3209 (67.2%) of 4772 eligible adults. The median age was 37 years (range 20-92), 57.3% were female, 4.6% reported a history of typhoid fever and 0.3% reported typhoid vaccination. Anti-Vi antibody titers tested in Vietnam were <1:40 in 2759 (86.0%), 1:40 in 194 (6.0%), 1:80 in 168 (5.2%), 1:160 in 57 (1.8%), and ≥1:320 in 31 (1.0%). On re-testing in the USA, an additional 19 sera with titers ≥1:160 were identified. We collected 589 rectal swabs from 103 (96.3%) of 107 persons with Vi antibody titers ≥1:160 and 183 swabs from 33 persons with antibody titers <1:80. No Salmonella Typhi was isolated. Conclusions: Community-based serologic screening is a feasible, but impractical method for identifying chronic Salmonella Typhi carriers. Background levels of anti-Vi antibody titers in this endemic area may be high despite a low prevalence of chronic carriers.