Grant: Travel Awards - Institute Community Support

Asymptomatic foci of malaria may be important reservoirs of parasites and are difficult to detect. A targeted active case detection system using symptomatic cases that present at rural health centres during the low transmission season in the Choma and Namwala districts of Zambia was conducted in 2009. Results of this pilot study indicated that this system appears to be able to identify more cases of asymptomatic asexual parasite and gametocytes carriers than controls. This study was repeated from July to November 2010 with an increased sample size to further validate the findings. The residence of all rapid diagnostic test (RDT) confirmed cases of malaria from participating rural health centres (RHC) during the low transmission season were located. Two controls per case were selected from the registries of the same RHC on the same day where the case presented. All consenting residents of the selected homesteads completed a questionnaire and were screened for malaria using microscopy, RDT, and nested-PCR. RT-PCR was conducted on all PCR positive samples to detect sexual stage parasites. In total, 218 and 408 participants residing in 40 case and 70 control homesteads, respectively, were screened. Unadjusted analysis resulted in case homesteads having 1/4% prevalence of malaria by RDT and 1.2% in control homesteads (Fisher's Exact p-value=1.0: OR=1.11 95% CI=0.17-5.76). However, when data were stratified by proximity to permanent rivers, those living greater than 1km away from a river had 2.2 greater odds of being RDT positive for malaria compared to controls (95% CI: 0.29-16.74; Fisher's Exact p-value=0.38). THe odds ratio for those living within 1km of rivers could not be calculated but the Fisher's Exact p-value was 0.51. The molecular analysis is ongoing.