Decreased microfilarial load and its effect on the calculation of prevalence and the rate of false negatives in the detection of onchocerciasis.

It has been shown in the epidemiological evaluation of onchocerciasis that the method of taking two or more snips per person contains information about the probabilities of false negatives which can be extracted and used to improve the prevalence estimates. Using the method of maximum likelihood, one can obtain expressions for estimating the prevalence, adjusted for the false negatives, and for estimating the proportion of false negatives. The variances of all estimates are also available, making confidence interval estimation possible.