Development of rapid assessment procedures for the delimitation of lymphatic filariasis-endemic areas

Lymphatic filariasis caused by Wuchereria bancrofti is a major public healt h problem in 73 tropical and subtropical countries including India. Delimit ation of endemic areas is essential to plan control operations. The current method of night blood survey (NBS) for delimitation is cumbersome, time-co nsuming and expensive. Therefore, there is a need to develop assessment pro cedures which can rapidly delimit endemic areas. For this purpose we evalua ted three procedures: direct interviewing of key informants using structure d questionnaires, an indirect method of a self-administered questionnaires to key informants and physical examination by health workers for the presen ce of chronic filarial disease. Thirty rural communities in a filariasis-en demic region in Cuddalore district in Tamil Nadu State in southern India co nstituted the study population. The determination of filariasis endemicity in the village communities assessed by the above procedures was compared in terms of rapidity, specificity, sensitivity and cost with the microfilaria rate and disease rate obtained by night blood sample survey and clinical e xamination by physicians. Prevalence score, control preference score and we ighted mean number of cases with filarial disease per village were calculat ed using the key informant questionnaire techniques. While the prevalence a nd control preference score showed low sensitivity and moderate specificity , weighted mean number of cases showed high sensitivity and moderate specif icity in identifying endemic villages. The prevalence of disease as determi ned by the physical examination of a sample population by health workers wa s highly sensitive in identifying communities endemic for filariasis. The d egree of association between the disease rates estimated by physician and t rained health workers was significant (r = 0.56; P < 0.05). These observati ons suggest that the weighted mean number of cases per village obtained thr ough key informant techniques may be considered at a primary level to crude ly identify endemic areas, followed by physical examination by health worke rs for filariasis, since it is relatively cheap and rapid.