Estimating the intensity of infection with Schistosoma japonicum in villagers of leyte, Philippines. Part I: a Bayesian cumulative logit model. The schistosomiasis transmission and ecology project (STEP).

Intensity profiles for helminths are used to describe population infection status, monitor effectiveness of control programs, and provide accurate data to validate transmission models. This study aims to accurately predict age/gender specific intensity profiles of endemic schistosomiasis japonica infection in the Philippines. Poor sensitivity of the Kato-Katz test and large heterogeneity in infection levels across villages complicate these predictions. Data from 1,989 individuals living in three endemic villages were analyzed with a Bayesian cumulative-logit model adjusting for nonproportional odds, variation between villages, and measurement error. The posterior uncertainty regarding the proportion of individuals in each egg category was high compared with that estimated using a model ignoring measurement error and villages' heterogeneity. The intensity profiles were very different in children less than 7 years old compared with older children and adults. This model could easily be adapted to other parasitic infections or outcomes where an analysis by category would be recommended.