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Bull World Health Organ. 1992;70(3):293-6.

Insecticide-impregnated bed nets for malaria control: a review of the field trials.


Insecticide-impregnated bed nets act as a physical barrier to repel and kill mosquitos. Community intervention trials suggest that these nets are effective in preventing malaria-related mortality and morbidity--but not malaria infection--in areas of low and moderate transmission; the results from areas of high transmission are not so encouraging. Comparison of the results from these trials and their interpretation are difficult because of variations in the epidemiology of malaria and several methodological flaws. Problems such as defining appropriate health indicators, monitoring bed-net usage, introducing bed nets randomly, selecting adequate controls, performing statistical analysis, and comparing bed nets with other available interventions are considered. Further community intervention trials are needed, paying attention to the methods and to assessment of their impact on malaria.


Researchers have conducted various field trials of insecticide impregnated bed nets for malaria control in the sub-Saharan African countries of Burkina Faso, the Gambia, Kenya, Sudan, and Tanzania, and in Malaysia and Papua New Guinea. Results show that local circumstances determine the degree to which bed nets protect against malaria. Bed nets are more successful at reducing the number of infective bites where mosquitoes feed inside and late at night and do not just bite humans. The bed nets form a physical barrier between humans and mosquitoes. They also repel and kill the mosquitoes. Researchers distributed bed nets to everyone in a community in most field trials to incorporate the mass effect in evaluating the health effect of the nets. Prevalence of malaria infections fell consistently in the field trials but most declines were not significant. On the other hand, the declines in parasite density and incidence of clinical malaria were significant (p.05). 1 trial measured malaria-related mortality. It found that the bed nets were more effective in protecting against malaria-related mortality than malaria morbidity. This may be due to a decline in the sporozoite load from mosquitoes resulting in protection against super infection. Methodological problems with community level interventions prevent researchers from making clear conclusions. For example, health professionals have not standardized the definition of clinical malaria. Using child mortality as a health indicator is hampered by the indirect effect of malaria on mortality and by other causes of death. Another problem is that distribution of bed nets does not guarantee usage. Obstacles also arise in randomization, determining controls and sample size, and in comparing other measures, e.g., DDT house spraying, with bed nets. Further research is needed that adequately addresses methodological problems as they must also be addressed in malaria vaccine trials.

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