Longitudinal malaria studies in rural north-east Thailand: demographic and temporal variables of infection.

A prospective longitudinal study of malaria incidence was carried out in randomly selected samples of the population in the villages of Bu Phram and Tablan, north-east Thailand. During the 10-month study period 46% of the 252 persons followed up experienced a falciparum parasitaemia, and 23% a vivax parasitaemia. The peak of the cases occurred during a 10-week period from late May to the end of July, with transmission apparently continuing, at lower levels, throughout the remainder of the study period. Falciparum infection rates were higher for residents of Bu Pham; vivax infection rates were the same in both villages. Certain indices declined with age in Bu Phram but not in Tablan residents. Parasite rates were higher for males than for females. Age-specific rates did not vary predictably. Infection of children aged less than one year was rare.