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

Abstract

Most researehers rely only on large samples fol' Ihe assessment of onchoeerciasis prevalence in eomrnunities where il is endemic . However, beeause of the large population that must be included in the sample and the cost of surveys, severa! alternative methods are being explored. One is Ihe seleetion of a small "at risk" sample of 30 persons from eaen eomrnunity lo determine the level of onchoeercal endemicity. In this study both the Small Sample Survey (SSS) and Ihe Complete Enumeration Survey (CES) techniques were IIsed lo determine the prevalence and intensity of onchocerciasis infeetíon in sixteen comrnunities in Dakka district, Nigeria, using conventional epidemiological procedures. The SSS showed Iha! 82.3% of 390 at risk persons were microfilarial positive wíth a mean microfilaria density (MFD) oi 90.9 microfilaria per skínsnip (MF/SS) and six comrnunities were classified as hyperendemic (prevalence beyond 59.9%). The CES of 1529 persol1s produced a coun! of 78.2% positivity and a MFD of 88.44 MF/SS. For each of tlle physical symptoms of Ihe disease and the MFD, computed T-Ies! values showed that ¡he SSS gives an estimate Iha! is impressively close lO tlle CES in Ihe estimation of the prevalence of onchocerciasis in a community des pite its low cosí.