The development and validation of a risk score for household infestation by Triatoma infestans, a Bolivian vector of Chagas disease

Chagas disease, primarily spread in Bolivia by the vector Triatoma Infestans, persists as an important public health problem. Preventative insecticide campaigns target spraying on the basis of anecdotal evidence and there is a need for an accurate classification score to correctly identify 'at risk' houses. Data were collected from 337 households on 11 variables through the use of a standardised questionnaire and survey. Risk factors for infestation were identified and a risk score was developed and validated on a separate cohort of 165 houses. Five significant risk factors were identified: cracks in the walls of houses; adobe walls; junk in the peridomiciliary area; no insecticide spraying in the previous two years; and freely ranging animals. A risk score was generated and then calculated for each house. Three risk categories were defined: low, medium and high risk. In the development cohort the infestation rates were 2%, 18% and 69% respectively. The corresponding infestation rates in the validation cohort were 7%, 30% and 75% respectively. Sensitivity and specificity for this test were 81% and 84% and the positive predictive and negative predictive values were 71% and 90%. The risk score developed could be used to inform decision making in underfunded multilateral preventative initiatives.