title: Development and validation of a rapid epidemiological assessment tool for lymphatic filariasis.
Creators: name: Gyapong, JO
Publisher: name: London School of Hygiene & Tropical Medicine
Year: 1997
Subjects: subject: Medicine

description: The real burden of lymphatic filariasis in most endemic areas remain unknown even though it is a major public health problems in many tropical countries. This is particularly so in sub-Saharan Africa, primarily because the standard procedures for assessing communities at risk of the disease are cumbersome, time-consuming, expensive and very intrusive. The nocturnal periodicity of the parasite requires parasitological examinations to be done at night and thus it becomes logistically cumbersome to organize. As a result of the lack of data on the burden and distribution of the disease, health care managers do not put much priority on its control. The need
to develop instruments which are easy to use in the field to identify communities at risk is therefore paramount for the initiation of any control programme. The aim of this study was to develop and validate rapid epidemiological assessment tools for the community diagnosis of lymphatic filariasis, and in the future, use the tools to determine the distribution of the disease, identify high risk communities, and obtain sufficient information for planning a control programme in Ghana. The data collection methods used were:
• Key informant interviews and other qualitative data collection methods,
• Physical examination of a sampled population by trained health workers, and
• Filarial surface antigen assays of those who were physically examined.
These methods were validated using standard epidemiological techniques such as:
• Physician examination of the same individuals who were examined by the health worker, and,
• Night blood parasitological examination of the same individuals who had the antigen assays done on them.
The key informant interviews were qualitatively very useful in identifying communities at risk, and tracing people with overt chronic disease. The system of sending questionnaires through routine administrative systems worked very well. The return rate of the questionnaires was about 95%. The District Assemblies provided reliable information on the communities, but teachers provide more accurate figures when compared with existing data from those communities. Routine reports from health institutions, even though useful, grossly under estimated the burden of the disease in the community. This is because these reports were influenced by:
• physical accessibility and ability to pay for the services,
• socio-cultural beliefs associated with the disease,
• technical expertise and laboratory facilities available at the institution, and
• the quality of record keeping.
The prevalence of hydroceles was high in the communities (range = 4.5 - 40.75%, mean = 17.78%). The community microfilaria prevalence correlated very well with the community prevalence of hydroceles (r = 0.84). There was a generally high agreement between the health worker's clinical findings and that of the physician (Kappa&gt;0.85 in most instances). The prevalence of infection detected by the Og4C3 surface antigen was consistently lower than the standard night blood smears in all the 20 communities. Thus, even though the antigen test had been shown in the laboratory to have a sensitivity of about 99% and specificity of a similar value, it was not possible to replicate such a high sensitivity under field conditions using blood
collected on filter paper.
The findings of the study suggested that it is possible to obtain reliable and valid estimates of the burden of lymphatic filariasis at community level using a combination of cheap and non-invasive methods such as:
• Key person interviews,
• Examination of a random sample of the population by peripheral level health staff.
The antigen assays will however require further development for field use.