257 Am. J. Trop. Med. Hyg., 58(2), 1998, pp. 257–262 Copyright  1998 by The American Society of Tropical Medicine and Hygiene LA UNTADITA: A PROCEDURE FOR MAINTAINING WASHBASINS AND DRUMS FREE OF AEDES AEGYPTI BASED ON MODIFICATION OF EXISTING PRACTICES CATALINA SHERMAN, EDUARDO A. FERNANDEZ, ADELINE S. CHAN, REINA C. LOZANO, ELLI LEONTSINI, AND PETER J. WINCH Division de Enfermedades Transmitidas por Vectores, Ministerio de Salud Publica, Tegucigalpa, Honduras; Department of International Health, The Johns Hopkins University, School of Hygiene and Public Health, Baltimore, Maryland Abstract. Chlorine bleach and detergent are routinely used by householders in El Progreso, Honduras in the process of cleaning washbasins and drums, the two most important larval habitats of Aedes aegypti in the city. The efficacy of these materials in eliminating eggs, larvae, and pupae of Ae. aegypti was assessed under controlled conditions. The promising results obtained led to trials using a combination of chlorine bleach and detergent to apply to the walls of washbasins and drums as a method for eliminating eggs. The bleach maintained its ovicidal properties when mixed with detergent, and the detergent gave the mixture consistency so that it could be applied as a thin film to the walls. This new procedure was named the little dab (Untadita in Spanish) and allows households to direct their efforts against a stage of the mosquito life cycle that has been ignored in the past: the egg. The first confirmed cases of dengue in Honduras occurred in 1977. Since that time dengue transmission has become endemic, and large epidemics were documented in 1978, 1987, 1989, 1991, and 1995. 1 All four dengue serotypes are now circulating in the country, and there were at least 30 confirmed cases of dengue hemorrhagic fever during the most recent epidemic in 1995. The Integrated Dengue Con- trol Project has been conducting field research since 1991 on community participation in reduction of larval container habitats of the disease’s mosquito vector Aedes aegypti (Lin- naeus). The site for the research has been El Progreso, a rapidly growing city of 100,000 on the north coast of Hon- duras. 2 Storage of water for domestic use is common where water supply is deficient or unreliable. 3, 4 This applies to El Pro- greso, where rapid and unplanned growth has made it in- creasingly difficult for city authorities to supply all residents with basic services such as potable water. In this city, con- crete washbasins and metal drums account for 25–72% and and 8–20%, respectively, of the Ae. aegypti larval habitats, depending on the neighborhood and the season. 5 They play an important role in maintaining mosquito populations dur- ing the dry season when other common containers such as tires and metal cans are dry. Washbasins are rectangular, made of cement, and usually have a drain at the bottom. The surface of the water may be completely uncovered, or partially covered by a built-in hor- izontal washboard made of corrugated cement and used for washing clothing. In El Progreso, the water is used for wash- ing clothing and dishes, mopping, watering plants, bathing, and only rarely for cooking or drinking. The water is in constant use and runs out quickly, but the washbasin fre- quently is filled up again before being emptied completely, allowing mosquito larvae remaining at the bottom to com- plete their life cycle. Continuing interruptions of the water supply have led householders to construct larger washbasins, ranging in size from 380 to 1,110 liters. Metal drums have a volume of 204 liters and no drain at the bottom. In houses with a washbasin they are used as an additional container for water storage. Initially, the project instructed householders to clean their washbasins and drums at least once and preferably two or three times per week to keep them free of mosquito larvae. However, even where these recommendations were closely adhered to, little or no decrease could be observed in the percent of washbasins and drums harboring mosquito larvae, for the following reasons. 1) Cleaning the washbasin or drum frequently does not entail emptying it out completely. Regarding the drum, in particular, there is the added diffi- culty of the absence of a drain. When the containers are filled again, the remaining larvae can complete their life cy- cle. 2) The frequency of cleaning is irregular, depending on both the availability of water and the time constraints of the housewife, to whom the responsibility for cleaning usually falls. 3) The immediate aim of the person cleaning is usually to remove the algae found on the walls below the water line, and few people are aware that the eggs attached to the wall above the water line must also be removed to eliminate all mosquito larvae. Successful removal of the algae results in a washbasin that appears clean, yet the irregular scrubbing of the walls has removed few eggs. The remaining eggs can hatch and develop into adult mosquitoes within days. 4) The built-in washboard makes it difficult to clean all parts of the washbasin because it is difficult to clean either the underside of the washboard or the vertical walls immediately below it, both of which were found in our trials to contain the highest quantity of deposited eggs. 5) In trials conducted in our lab- oratory, subsequent to scrubbing of egg-infested walls with a commercially available brush, many eggs were found to survive and later hatch either at the bottom of the washbasin or in the bristles of the brush. In one experiment, 2,079 eggs were initially located on the wall of a drum. Thirty seconds of scrubbing with the brush resulted in 442 (21%) being removed from the wall, but hatching as larvae in the water at the bottom, and 189 (9%) becoming wedged in the bristles of the brush and hatching after the brush was immersed in water. Brushing therefore only eliminated 64% of the eggs in this case. It was obvious that scrubbing with a brush in isolation was an ineffective method of control. In previous phases of the project, it was believed that the irregular water supply, coupled with the ineffective methods used by householders to clean washbasins and drums, indi- cated that neither was amenable to cleaning-related control methods. 6 A number of alternative approaches were consid-