The role of dirt floors and of firewood in rural dwellings in the epidemiology of Chagas' disease in Costa Rica.

In an endemic area of Chagas' disease in Costa Rica, 50 houses infested with Triatoma dimidiata were re-examined after a period of 14-17 years. Criteria used were two socioeconomic parameters which are closely associated with the presence of the bugs: colonies of triatomines inside houses are favored by the presence of a dirt floor, and stored firewood is an excellent refuge for insects outdoors. Indoor infestation was completely eliminated from nine of 13 houses in which the floors had been changed from dirt to concrete during this period, and nearly eliminated from the other four, supporting the hypothesis that the disappearance of dirt floors makes it difficult for the bugs to thrive inside houses. Of the 21 houses that lost the infestation (inside, outside, or both), firewood had been eliminated in 13, and of 29 houses that remained infested firewood had been eliminated in only two. An inverse relationship was found between distance of firewood piles from the house and presence of bugs. It is supposed that a colony of insects frequently starts in stored firewood and then moves into the household if a dirt floor is present. Removal of firewood and replacement of dirt floors by concrete would provide good prophylactic measures against the transmission of Chagas' disease in areas where T. dimidiata is the vector.