Impact of fly control on childhood diarrhoea in Pakistan: community-randomised trial

Abstract

Background: Several million children are killed each year by diarrhoeal diseases; preventive strategies appropriate for developing countries are vital. Despite strong circumstantial evidence that flies are vectors of diarrhoeal diseases, no convincing studies of the impact of fly control on diarrhoea incidence in developing countries have been reported. We undertook a randomised study of the effect of insecticide spraying on diarrhoea incidence.

Methods: Six study villages were randomly assigned to two groups. Flies were controlled through insecticide application in group A in 1995 and in group B in 1996. In 1997 the effectiveness of baited fly traps was tested in group A villages. Diarrhoea episodes were monitored in children under 5 years through mothers' reports during weekly visits by a health visitor. Fly density was monitored by use of sticky fly-papers hung in sentinel compounds.

Findings: During the fly seasons (March-June) of both 1995 and 1996, insecticide application practically eliminated the fly population in the treated villages. The incidence of diarrhoea was lower in the sprayed villages than in the unsprayed villages in both 1995 (mean episodes per child-year 6.3 vs 7.1) and 1996 (4.4 vs 6.5); the reduction in incidence was 23% (95% CI 11-33, p=0.007). At times other than the fly season there was no evidence of a difference, in diarrhoea morbidity between sprayed and unsprayed villages. Fly density data for 1997 indicate the ineffectiveness of baited traps in this setting.

Interpretation: Fly control can have an impact on diarrhoea incidence similar to, or greater than, that of the interventions currently recommended by WHO for inclusion in diarrhoeal disease control programmes in developing countries. This important finding needs confirmation in other settings in developing countries. Technologies and practices that interrupt disease transmission by flies need to be developed and promoted.

PIP: Since circumstantial evidence suggests that flies are vectors of diarrheal diseases, a randomized study of the effect of insecticide spraying upon the incidence of diarrhea was conducted near the town of Peshawar, North West Frontier Province, Pakistan. 6 study villages were randomly assigned to 2 groups, with flies controlled through the twice weekly application of ultra low volume space spraying with insecticide in group A in 1995 and in group B in 1996. The insecticide used was Aqua K-Othrine, a water-based formulation of deltamethrin, applied at a dose of 0.5-1.0 g of active ingredient per hectare by Porta-Pak sprayers. In 1997, the effectiveness of baited fly traps was tested in group A villages. The incidence of diarrhea episodes was monitored in children under age 5 years through mothers' reports during weekly visits by a health worker, and fly density was monitored using sticky fly-papers hung in sentinel compounds. During the fly seasons of March-June in 1995 and 1996, the application of insecticide almost eliminated the fly population in the treated villages. The incidence of diarrhea was lower in the sprayed villages than in the unsprayed villages in both 1995 and 1996, for an overall 23% reduction in incidence. At times other than the fly season, no evidence was observed of a difference in diarrhea morbidity between sprayed and unsprayed villages. Fly density data for 1997 found the baited traps to be ineffective.