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

Abstract

SummaryLymphatic filariasis caused by Wuchereria bancrofti is a major public health problem in 73 tropical and subtropical countries including India. Delimitation of endemic areas is essential to plan control operations. The current method of night blood survey (NBS) for delimitation is cumbersome, time-consuming and expensive. Therefore, there is a need to develop assessment procedures which can rapidly delimit endemic areas. For this purpose we evaluated three procedures: direct interviewing of key informants using structured questionnaires, an indirect method of a self-administered questionnaires to key informants and physical examination by health workers for the presence of chronic filarial disease. Thirty rural communities in a filariasis-endemic region in Cuddalore district in Tamil Nadu State in southern India constituted 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 examination by physicians. Prevalence score, control preference score and weighted mean number of cases with filarial disease per village were calculated using the key informant questionnaire techniques. While the prevalence and control preference score showed low sensitivity and moderate specificity, weighted mean number of cases showed high sensitivity and moderate specificity in identifying endemic villages. The prevalence of disease as determined by the physical examination of a sample population by health workers was highly sensitive in identifying communities endemic for filariasis. The degree of association between the disease rates estimated by physician and trained health workers was significant (r ϭ 0.56; P Ͻ 0.05). These observations suggest that the weighted mean number of cases per village obtained through key informant techniques may be considered at a primary level to crudely identify endemic areas, followed by physical examination by health workers for filariasis, since it is relatively cheap and rapid.

The global distribution and transmission limits of lymphatic filariasis: past and present

“…Alternatively, the presence of W. bancrofti antigenaemia can be detected using the ICT card test [33][34][35] and presence of specific IgG4 antibodies to Brugia spp can be detected using the Brugia Rapid™ test [36][37][38]. Surveys for the mapping of LF have been based on a variety of sampling designs, including the rapid geographical assessment of Bancroftian filariasis (RAGFIL) method [29,63], lot quality assurance sampling [64,65], population-based household surveys [66] and sentinel site surveys [43,67,68], with the choice of survey methodology dependent on available resources and the stage of the control programme [69].…”

A geostatistical analysis of the geographic distribution of lymphatic filariasis prevalence in southern India.

“…Within each village, 50 adult males above 15 years of age, and 40 households were selected for estimating antigenemia prevalence within the community using the ICT card test. 26,27 The number of households (40) to be sampled per village was based on the finding that on average in rural India 2 to 3 adult males would be available per household; the selection of households themselves was performed by first listing the total number of households in the village followed by estimating the sampling interval (total number of households/40) for the systematic selection of household units for the study. The first household is selected randomly (by choosing a number randomly between one and the sampling interval), and the others are chosen by the cumulative addition of the sampling interval to each previous number as described elsewhere.…”

“…28 As far as the data for microfilaria (mf) prevalences are concerned, these villages were randomly selected from three districts under different field studies conducted by the Vector Control Research Centre(VCRC). 26,27,29 In each village, 7-10% of the population from randomly selected households were included in the microfilaraemia surveys. Microfilaria examination was undertaken using 20 ccm blood smears collected from each individual selected for these surveys.…”

“…This investigation forms part of a multicountry study initiated by the World Health Organization (WHO) Rapid Geographical Assessment of Bancroftian Filariasis (RAGFIL) program, 25 which advocated using a sampling grid of either 25 × 25 km or 50 × 50 km for selecting communities to undertake rapid filariasis prevalence surveys (by the application of rapid assessment procedures (RAP) surveys of filariasis prevalence, such as physical examination by the health workers (PEHW) 26 or estimation of parasite antigenemia prevalence by the use of the immunochromatographic card test (ICT) 27 to map and investigate filariasis distribution. While the primary analysis is based on filariasis antigeneamia prevalence data obtained from 79 communities selected from an endemic region in South India using the 25 × 25 km grid sampling framework, comparison is also made with the spatial structure of microfilaraemia prevalence data obtained from a random sample of 119 villages within the same region (used for a separate study validating different RAP methods 26 ), to illustrate the importance of spatial sampling scale for the detection and quantification of spatial structure.…”

“…While the primary analysis is based on filariasis antigeneamia prevalence data obtained from 79 communities selected from an endemic region in South India using the 25 × 25 km grid sampling framework, comparison is also made with the spatial structure of microfilaraemia prevalence data obtained from a random sample of 119 villages within the same region (used for a separate study validating different RAP methods 26 ), to illustrate the importance of spatial sampling scale for the detection and quantification of spatial structure. These results are discussed in light of the WHO advocacy of a common grid dimension for grid sampling of communities for the rapid mapping and spatial analysis of filariasis distribution in diverse endemic regions.…”