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Title: The Gambian National Impregnated Bed Net Programme: evaluation of effectiveness by means of case-control studies.
Author: D'Alessandro U, Olaleye B, Langerock P, Bennett S, Cham K, Cham B, Greenwood BM.
Journal: Trans R Soc Trop Med Hyg; 1997; 91(6):638-42. PubMed ID: 9509168.
Abstract:
Two case-control studies, one on mortality and the other on malaria morbidity, were carried out in order to evaluate the impact of the Gambian National Insecticide Bed Net Programme during the second year of intervention and to explore the feasibility of such a study for the evaluation of programme effectiveness. For the mortality study, children 1-9 years old who died during the 1993 rainy season were matched by age and sex with 2 healthy controls from the same village. For the morbidity study, children 1-9 years old attending Fatoto or Jahalia Health Centres in The Gambia and who had fever and parasitaemia > or = 5000/microL were matched by age with a child attending the health centres without fever or parasitaemia. An additional healthy control was recruited from the case's village. No impact of insecticide-treated bed nets on mortality was detected and this was in keeping with the results obtained by prospective surveillance. A protective effect of insecticide-treated nets on malaria morbidity was detected when cases were compared with controls recruited at the health centres. However, this disappeared when cases were compared with controls recruited from the cases' villages. The mortality case-control study suggested that reducing the time between onset of disease and treatment may have an important impact on childhood mortality. In order to calculate programme cost-effectiveness, important for informed resource allocations to be made by health managers, it is essential to obtain evidence of effectiveness. This can be done by means of case-control studies, which are easier to carry out and require fewer resources than prospective surveillance. Nevertheless, it is necessary to be conscious of their pitfalls, particularly of the bias involved in the choice of cases and controls. The measurement of insecticide on the nets of the cases or controls is essential for such studies. The impact of the Gambian National Impregnated Bed Net Program was evaluated during its second year of implementation through two case-control studies on malaria mortality and morbidity. The first study matched 167 children 1-9 years of age who died during the 1993 rainy season with two healthy controls (n = 334) of the same age and sex from the same village. The second study matched 143 children 1-9 years of age attending Fatoto or Jahalia Health Centers with fever or parasitemia with a child the same age attending the health centers without these symptoms and an additional healthy control from the same village. The mortality study failed to document any protective effect of insecticide-treated bed nets. Child survival was more closely linked to consultation with a village health worker during serious illness, household availability of chloroquine tablets, sponging, and maternal awareness of fever and convulsions as symptoms of malaria. A protective effect of the bed nets on malaria morbidity was revealed when cases were compared with health center controls, but this effect disappeared when cases were compared with controls from the same village. Going to bed early and father having a job other than working on the family farm were the two variables associated with significant protection against malaria in the multivariate analysis. Case-control studies are easier to conduct and require fewer resources than large prospective community-based studies. However, it is recommended that any future such studies of malaria control programs clarify the criteria used to select cases and controls and incorporate insecticide measurements of study nets.

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