Micro-spatial variation in filarial disease and risk of developing disease associated with microfilaremia in urban situation.

Clinical and parasitological surveys were carried out concurrently during 1986 in Pondicherry. The analyses showed that there was no significant micro-spatial variation in prevalence of total diseases (acute and chronic) and the manifestations such as hydrocele and lymphedema in the different zones and stations of Pondicherry urban area, a stable endemic area. Analyses on different filariometric indices in different stations showed a significant correlation between disease and mf prevalence (r = 0.4106; p = 0.037). The prevalence of disease and hydrocele in microfilaremic individuals (9.4% and 20.0% respectively) was higher compared to that observed in amicrofilaremic persons (6.4% and 11.2% respectively). The relative risk (RR) of parasite carriers developing disease (any manifestations) was marginally higher compared to amicrofilaremic persons (1.18). However, the RR of developing hydrocele manifestation due to microfilaremia was much greater (1.5) compared to amicrofilaremic persons. The attributable risk (AR) due to microfilaremia for developing hydrocele was 0.05. This suggests that although the risk is high in mf carriers, there might be alternate ways of developing disease without the infected person becoming microfilaremic. The limitations of point prevalence data on understanding complex dynamics of infection and disease are discussed.