Comparison of two sample survey methods for hyperendemic onchocerciasis and a new focus in Dakka, Nigeria.

Most researchers rely only on large samples for the assessment of onchocerciasis prevalence in communities where it is endemic. However, because of the large population that must be included in the sample and the cost of surveys, several alternative methods are being explored. One is the selection of a small "at risk" sample of 30 persons from each community to determine the level of onchocercal endemicity. In this study both the Small Sample Survey (SSS) and the Complete Enumeration Survey (CES) techniques were used to determine the prevalence and intensity of onchocerciasis infection in sixteen communities in Dakka district, Nigeria, using conventional epidemiological procedures. The SSS showed that 82.3% of 390 at risk persons were microfilarial positive with a mean microfilaria density (MFD) of 90.9 microfilaria per skinsnip (MF/SS) and six communities were classified as hyperendemic (prevalence beyond 59.9%). The CES of 1529 persons produced a count of 78.2% positivity and a MFD of 88.44 MF/SS. For each of the physical symptoms of the disease and the MFD, computed T-test values showed that the SSS gives an estimate that is impressively close to the CES in the estimation of the prevalence of onchocerciasis in a community despite its low cost.