The impact of insecticide-treated bed nets on malaria incidence in Ixcan, Guatemala and the associated identification of spatial clusters of malaria

This project was conducted to assess the efficacy of insecticide-treated bed nets (ITNs) in protecting people against malaria infection in a rural area of Northern Guatemala characterized by low malaria endemicity with unstable and seasonal transmission. While studies from sub-Saharan Africa have indicated that ITNs are highly efficacious, likely due to favorable conditions such as stable malaria transmission and Anopheles gambiae or An. funestus as primary malaria vectors, a number of studies from other areas of the world, including Latin America, have shown either no protective efficacy of ITNs or even an increased risk of infection for individuals using ITNs. For this purpose, a cluster randomized controlled trial was conducted in 2001 in Ixcán, Guatemala to compare the risk of malaria between 13 intervention villages in which all individuals were provided with an ITN and 13 control villages in which no ITNs were provided. The rates of malaria were measured during two cross-sectional pre-intervention surveys and one post-intervention survey. Results showed a significantly higher risk of malaria infection for people living in intervention villages compared to those living in control villages (RR = 1.81, 95% CI 1.11 – 1.92). These results suggest that ITNs failed to provide protection against malaria in this area of Guatemala, although, notably, the rate of malaria for intervention villages was considerably magnified due to uncommonly high malaria rates in only two of the thirteen intervention villages during the post-intervention survey. It is essential to conduct more studies in areas of unstable malaria transmission to have a better understanding of the extent of ITN efficacy and to compare ITNs to other malaria control strategies such as prompt diagnosis and treatment, indoor residual spraying, vector control, or a combination of them. ^ In addition to the ITN efficacy study, a spatial and temporal evaluation of the study area (the same area in which the ITN efficacy study was conducted) was carried out using two statistics, i.e., the local Moran’s I and the Getis-Ord*(d), to determine whether malaria aggregated in the form of clusters (or outliers). This analysis was performed to reveal patterns of malaria distribution in an area of low malaria endemicity since a thorough understanding of the spatial and temporal patterns of malaria distribution is essential for targeted malaria control programs. Clusters of malaria exhibited high spatial and temporal variations, suggesting that surveillance and spatial analysis should be conducted on a regular basis to create targeted malaria control activities. ^ Overall, results from the ITN efficacy study confirm the lower efficacy of ITNs in an area of unstable and seasonal malaria transmission characterized by seemingly unfavorable conditions such as local malaria vectors ( An. albimanus) that tend to feed when humans are not sleeping and the high proportion of Plasmodium vivax malaria that favors relapses. The results of the spatial analysis, which indicate marked spatial and temporal variations in malaria distribution, also seem to be consistent with a context of unstable and seasonal malaria where the location of clusters over a relatively short period of time (approximately 1 year in this study) can vary considerably.