Abstract: Objective To investigate the relationship of the intensity of Schistosoma japonicum infection with the variation in individual egg counts. Methods Stool specimens were collected from residents in a village in Jiangxi Province and examined with Kato-Katz thick smear method for seven consecutive days. Two smears were prepared and microscopically examined for each specimen. 570 individuals completed the investigation. Coefficient of variation （CV） was used to assess the intra-individual variation of the egg counts， in relation to the demographic characteristics including age，sex，occupation，and the intensity of infection. Results The proportion of individuals with at least one positive finding increased from 33.0% in a single measurement to 56.5% by seven measurements （P<0.01）. The average intensity of infection in a single Kato-Katz test （111.06 EPG） was markedly higher than the average accumulated intensity of infection （42.51 EPG）. Variation of intra-individual: the variation of CV in female infected subjects was higher than males（P<0.05）. The variation of CV in 0-9 age group was higher than other age groups （P<0.05）. The lowest variation of CV was detected in fishermen （P<0.05），but no statistical difference was found among other occupation groups. With an increase of the intensity of infection， the variation of CV decreased gradually. A negative correlation was observed between the variation of CV and the intensity of infection（r=-0.717， P<0.01）. There was no significant difference in variation of CV between males and females，age and occupation groups when data were stratified according to the intensity of infection （P>0.05）. Conclusion The prevalence and intensity of S. japonicum infection by single Kato-Katz test was obviously lower than the real figures. The intensity of infection may be an essential factor that affects the intra-individual variation of egg counts.

Key words: Schistosoma japonicum, Egg count, Variation, Kato-Katz method