title: Associations between schistosomiasis and the use of human waste as an agricultural fertilizer in China.
abstract: BACKGROUND
  Human waste is used as an agricultural fertilizer in China and elsewhere. Because the eggs of many helminth species can survive in environmental media, reuse of untreated or partially treated human waste, commonly called night soil, may promote transmission of human helminthiases.
  
  
  RESULTS
  We conducted an open cohort study in 36 villages to evaluate the association between night soil use and schistosomiasis in a region of China where schistosomiasis has reemerged and persisted despite control activities. We tested 2,005 residents for Schistosoma japonicum infection in 2007 and 1,365 residents in 2010 and interviewed heads of household about agricultural practices each study year. We used an intervention attributable ratio framework to estimate the association between night soil use and S. japonicum infection. Night soil use was reported by half of households (56% in 2007 and 46% in 2010). Village night soil use was strongly associated with human S. japonicum infection in 2007. We estimate cessation of night soil use would lead to a 49% reduction in infection prevalence in 2007 (95% CI: 12%, 71%). However, no association between night soil and schistosomiasis was observed in 2010. These inconsistent findings may be due to unmeasured confounding or temporal shifts in the importance of different sources of S. japonicum eggs on the margins of disease elimination.
  
  
  CONCLUSIONS
  The use of untreated or partially treated human waste as an agricultural fertilizer may be a barrier to permanent reductions in human helminthiases. This practice warrants further attention by the public health community.
authors.affiliation: Department of Environmental and Occupational Health, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Carlton
authors.affiliation: Institute of Parasitic Diseases, Sichuan Center for Disease Control and Prevention, Chengdu, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Institute of Parasitic Diseases, Sichuan Center for Disease Control and Prevention, Chengdu, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhong
authors.affiliation: Division of Biostatistics, School of Public Health, University of California, Berkeley, California, United States of America.
authors.forename: Alan
authors.initials: A
authors.lastname: Hubbard
authors.affiliation: Center for Occupational and Environmental Health, School of Public Health, University of California, Berkeley, California, United States of America.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Spear
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D005243:Feces / Q000469:parasitology*; D005308:Fertilizers; D006801:Humans; D012554:Schistosomiasis japonica / Q000453:epidemiology / Q000635:transmission*
chemical_list: D005308:Fertilizers