The morbidity attributable to Schistosoma japonicum infection in 3 villages in Dongting Lake region, Hunan Province, PR China

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Abstract
In common with other helminth infections, symptoms associated with Schistosoma japonicum infection have a low specificity, and many infections are asymptomatic. The presence of the parasite in a sick individual from an endemic area does not mean that S. japonicum is the aetiological agent. However, estimates of the proportion of all symptomatic episodes in a community attributable to S. japonicum infection can be used to determine its public health impact. Using parasitological and morbidity survey data from 3 villages in China, the fractions of diarrhoea, bloody stool, and abdominal pain episodes that were attributable to S. japonicum infection were estimated. The association between hepatomegaly and S. japonicum infection was also assessed. For all morbidity indicators, it was found that individuals with higher infection intensities were at greater risk of morbidity. The highest risk indicator of morbidity associated with S. japonicum infection was bloody stools. Logistic regression revealed that factors related to village and sex were important confounders of the relation between infection and the risk of morbidity. The fraction of the population in each village estimated to be suffering morbidity attributable to S. japonicum infection was low, due to the low prevalence of infection. However, the results suggest that some sick individuals may have been diagnosed as false negatives for S. japonicum infection.