Risk factors for infection with malaria in a low endemic community in Bataan, the Philippines

The patterns of malaria morbidity and mortality can vary with the level of malaria transmission in a given area. We carried out two annual cross-sectional surveys in the hypoendemic malarious community of Morong, the Philippines, to examine epidemiologic and sociobehavioural risk factors for infection. In both surveys, the greatest risk of having malaria was associated with place of residence. For example, in the first survey, living in an area where more than 50% of the community had a high IFAT titer had an adjusted odds ratio (OR) of 33.7. A range of activities thought to be associated with risk were examined, but in the first survey, only frequent nocturnal visits to the forest were found to be a significant risk factor overall (adjusted OR; 2.65; 95% CI 1.48, 4.73), but this phenomenon was primarily observed among individuals residing in the lowest prevalence areas. In the second survey, where only the area with a relatively high prevalence of malaria was sampled, no association with activities was found. In this survey, significant factors associated with malarial infection were: being a migrant (adjusted OR 1.97; 95% CI 1.33, 2.92), being male (adjusted OR 1.63; 95% CI 1.10, 2.43) and age 30 years or less (adjusted OR 0.29 for age > 30 years; 95% CI 0.16, 0.52). The data suggest that in low-endemic communities like Morong, Bataan, control efforts should be primarily directed to focal areas identified by serology, particularly among migrants and among male young adults.