SPATIAL PATTERNS OF HUMAN WATER CONTACT AND SCHISTOSOMA-MANSONI TRANSMISSION AND INFECTION IN 4 RURAL-AREAS IN MACHAKOS DISTRICT, KENYA

This paper presents the results of microgeographical studies of human water contact behavior and Schistosoma mansoni transmission levels and intensity of infection in four rural areas in Machakos District, Keny a. The relationship between intensity of infection (geometric mean egg counts) in 3502 persons aggregated in 120 household clusters and eigh t independent variables was investigated using straight and stepwise l inear regression and mapping techniques. Results indicate that the two water contact variables, mean frequency per person and mean duration per person, as well as mean number of sites used per person, a transmi ssion index and mean distance to the most frequently used site were th e strongest predictors of geometric mean egg counts. All three distanc e variables were usually negatively associated with infection although intensity of infection and water contact declined relatively slowly w ith distance from the streams. This pattern appears to be owing to a c ombination of the relatively short distances, a general lack of safe a lternative water sources and the use of more distant water contact sit es both inside and outside the study area during periods of drought. T he study of snail-to-man transmission identified number of infected sn ails as the major transmission variable and number of contacts as the major predictor variable. Mapping of total egg counts at the household cluster level and total number of infected snails revealed spatial as sociation with transmission sites. All results varied considerably bet ween study areas, owing to differences in exposure levels, transmissio n patterns and environmental factors. Findings are discussed in relati on to the epidemiology and control of schistosomiasis and suggestions are made for further spatial studies. (C) 1997 Elsevier Science Ltd.