Rapid assessment of onchocerciasis prevalence and a model for selecting communities for ivermectin distribution in West Africa.

Analysis of the prevalence of onchocerciasis in an area of north-east Nigeria indicates that clinical symptoms are generally good predictors of the rate of onchocerciasis infection and of the mean microfilarial density in infected individuals. However, differences between regions and anomalous communities within regions make reliance on a single indicator dubious. Use of multivariate equations was tested, but offered little improvement over bivariate ones and an algorithmic approach, making use of local knowledge of factors which might complicate interpretation, is proposed instead. The framework is suggested as a basis for screening, although a larger database is required to produce definitive equations.