Prevalence and incidence of onchocerciasis as baseline data for evaluation of vector control in San Vicente Pacaya, Guatemala.

The aim of this study was to estimate the incidence rate of onchocerciasis as measured by skin biopsy during field surveys carried out in San Vicente Pacaya, Guatemala from 1977 through 1979. The age standardized prevalence rates for males and females were 44.6% and 19.9%, respectively, in 1979. There were annual incidence rates of 0.08 and 0.04 for males and females, respectively. The incidence rates seem to increase with age. Since the effect of false negatives will be greater in females than in males, these rates should be interpreted cautiously. Extremely high reversion rates (proportion of negatives in a later examination among positives at the first examination by skin biopsy) were observed; these figures might be explained mainly by false negatives due to the skin biopsy. However, it is suspected that some of the apparent reversion rates may also have been influenced by other factors, e.g., sex difference.