Epidemiology of malaria in a hypoendemic Brazilian Amazon migrant population: a cohort study.

The present study describes aspects of the epidemiology of malaria in a migrant population living in a hypoendemic area in Brazil using an open cohort study design. Rural settlement residents in Leonislândia, Peixoto de Azevedo, Mato Grosso, Brazil were followed from September 1996 to April 1997. At baseline, an interview and malaria diagnoses were carried out and spleen size was measured. Incident cases were detected through follow-up visits and laboratory records. Cox regression was used to assess risk factors for time to malaria onset. Eighty percent (n = 414) of the study population (n = 521) contributed follow-up data. Overall, malaria prevalence during any study visit ranged from 0.3% to 5.4% and the malaria incidence rate (IR) was 4.49 (95% confidence interval = 3.66, 5.46) per 100 person-months. The IR of Plasmodium vivax malaria was approximately four times higher than the IR for P. falciparum malaria during follow-up. Among individuals who had had malaria during his or her lifetime, 14.03% reported hospitalization (median duration = 3 days) and 70.1% reported days of work lost (median duration = 4 days for P. falciparum malaria and 3 days for P. vivax malaria) related to the last malaria episode. No important risk factor was associated with the malaria IR. The fact that neither work-related factors nor age was associated with the risk of malaria indicates that indoor/peri-domiciliary transmission by the local vector is more important or as important as workplace-related transmission.