The prevalence of
schistosomiasis due to S. japonicum is focally high in the lake regions of China, and
reinfection after treatment with
praziquantel is frequent. In this study, the total
reinfection rate among 740 treated persons was 12.9%. Factors associated with
reinfection were age and sex, water contact and the distance from homes to snail habitats. The
reinfection rate was higher among men (15.0%) than among women (8.3%). The frequency of water contact is the main factor in
reinfection. Among persons with more than 120 and 10-120 water-contact days, the
reinfection rates were 24.0% and 16.4%, respectively. The
reinfection rates among people living 0 m, 500 m and 1000 m from snail-ridden areas were 14.1%, 8.3% and 4.3%, respectively. Fishing was the most frequent reason for water-contact, followed by herding animals and playing in water;
reinfection rates among those engaging in these activities were 36.4%, 16.3% and 22.9%, respectively.
Reinfection is clearly a problem, and since much of it is connected with essential economic activities, the cycle of
infection and
reinfection is not likely to be broken until effective methods for eliminating reservoirs of infection are developed.