Usage of personal-protection measures against mosquitoes and the low prevalences of Wuchereria bancrofti microfilaraemia in the Indian city of Chennai.

The usage of personal-protection measures against mosquitoes and the prevalence of Wuchereria bancrofti microfilaraemia were assessed in different areas of the city of Chennai, a large urban area in southern India. Most of the households investigated (75% to 92%, depending on socio-economic status) used some form of personal protection (such as mosquito coils, vaporizing mats and liquids and mosquito nets). The study households spent a mean (S.D.) of 109.45 (141.65) Indian rupees/month on personal protection, such expenditure increasing significantly with increasing household income (F=2.95; P=0.03). Over the last three decades the prevalence of W. bancrofti microfilaraemia has been slowly declining in Chennai. Most of the 'moderate-income' areas of the city investigated in the present study appeared free of such microfilaraemia, and the prevalences recorded in about half of the low- and very-low-income study areas did not exceed 1.0%. The mean prevalences recorded in the moderate-, low- and very-low-income areas were 0.51%, 1.15% and 1.30%, respectively. Given their very low prevalences of microfilaraemia, relatively good housing, sanitation and health care and extensive use of personal-protection measures, the 100 million Indians living in (mostly urban) moderate- and high-income areas may not require active mass drug administrations (MDA) against lymphatic filariasis. The need to develop simple methods to stratify urban areas, into those that require and those that do not require active MDA, remains. If lymphatic filariasis is to be eliminated from India in a reasonable time-frame, at least as a public-health problem, MDA should now be focused on the poorer localities.