Influence of strain characteristics and immunity on the epidemiology of Campylobacter infections in Thailand.

To determine how strain differences and immunity affect the clinical expression of Campylobacter infections, we conducted a study of acute diarrheal disease in Thailand in which specimens from children with Campylobacter infections were cultured weekly for up to 12 weeks to determine the serotype-specific length of time of convalescent-phase excretion and rate of reinfection. Levels of immunoglobulin G to cell-surface antigens of C. jejuni were determined in another population of healthy children who were closely related by age and location to the children in the diarrheal disease study. Campylobacter species were initially isolated from 18% of 586 children under 5 years old with diarrhea; most isolates in Thailand belonged to serotypes commonly found in developed countries. C. coli was significantly less often associated with symptomatic infections and with bloody diarrhea than C. jejuni (P less than 0.001 and P = 0.045, respectively). The peak age of isolation and the peak level of immunoglobulin G to Campylobacter species occurred before 2 years of age. The mean duration of convalescent-phase excretion was 14 +/- 2 (standard error of the mean) days for children less than 1 year old and 8 +/- 2 days for children 1 to 5 years old (P = 0.02, t test). Infection with another Campylobacter serotype was found in 34% of 105 children during the 12-week follow-up period. The rate of reinfection in these children was 15% (range, 8 to 22%) each week. Hyperendemic exposure to Campylobacter species in Thailand confers immunity to infection that is associated with an early peak in specific serum antibodies and an age-related decrease in the case-to-infection ratio and duration of convalescent-phase excretion but does not prevent asymptomatic infections.