High prevalence of Wuchereria bancrofti infection as detected by immunochromatographic card testing in five districts of Orissa, India, previously considered to be non-endemic

India accounts for over one-third of the world's burden of lymphatic filariasis (LF). Although most coastal districts of Orissa state (eastern India) are LF-endemic, the western districts of Orissa are considered non-endemic. During a large-scale insecticide-treated bed net/microfinance trial, we tested one randomly selected adult (age 15-60 years) for LF from a random sample of microfinance-member households in five districts of western Orissa, using immunochromatographic card testing (ICT). Overall, 354 (adjusted prevalence 21%, 95%CI 17-25%) of 1563 persons were ICT positive, with district-wide prevalence rates ranging from 15-32%. This finding was not explained by immigration, as only 3% of subjects had ever lived in previously known LF-endemic districts. These results therefore suggest ongoing autochthonous transmission in districts where LF control programs are not operational. Our results highlight the importance of broad, systematic surveillance for LF in India and call for the implementation of LF control programs in our study districts.