Chagas disease: assessing the existence of a threshold for bug infestation rate.

To examine the existence of a possible threshold for the domestic infestation rate of Triatoma dimidiata, below which transmission becomes unlikely, a census was conducted in 59 Chagas disease endemic communities of El Salvador and Honduras. Entomological and serological tests were conducted targeting 4,083 households and 6,324 children between 6 months and 15 years of age. The overall domestic infestation rate of Triatoma dimidiata and seroprevalence among children were 12.9% and 0.49%, respectively. Communities with a domestic infestation rate at 8% or less consistently showed a seroprevalence of 0%. In communities with a domestic infestation rate above 8%, there was a wide range in seroprevalence. A domestic infestation rate of 8% could serve as the possible threshold below which transmission would become unlikely. The implementation of an 8% threshold for determining needs for universal insecticide spraying would lead to a 21% reduction in spraying-related costs.