The effect of oral and parenteral typhoid vaccination on the rate of infection with Salmonella typhi and Salmonella paratyphi A among foreigners in Nepal

We studied the incidence of enteric fever among travelers and foreign residents who attended an expatriate clinic in Kathmandu, Nepal, from February 1987 to June 1988. There were 42 cases of enteric fever; 20 were caused by Salmonella typhi and 22 by Salmonella paratyphi A. Among 18 unvaccinated foreigners who had enteric fever, S typhi was isolated from 67%, and S paratyphi A from 33%, a ratio similar to the local Nepalese population. Among 22 vaccinated foreigners, S typhi was isolated from 35%, compared with 65% with S paratyphi A. Nine percent of tourists had received the oral Ty21A typhoid vaccine. However, among seven vaccinated tourists who became infected with S typhi, four (57%) had received the oral vaccine. Thypoid vaccine efficacy for tourists was calculated and showed an overall protective rate of 90% against enteric fever in general, 95% protection against S typhi, and 72% to 75% protection against S paratyphi A. We conclude that typhoid vaccine should be recommended to all travelers to the Indian subcontinent, and since S paratyphi A is the predominant cause of enteric fever among vaccinated travelers, consideration should be given to an effective vaccine against S paratyphi A when that becomes available.