Abstract
BackgroundHuman 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.Methodology/Principal FindingsWe 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/SignificanceThe 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.
Highlights
People have collected human waste and used the material, called night soil, to fertilize agricultural crops [1, 2]
Human waste was used as an agricultural fertilizer in 56% and 46% of households surveyed in 2007 and 2010, respectively
44 49 a Crops planted by at least 10% of households in a given season are listed. b Rapeseed and wheat are grown in the winter season; rice, corn, vegetables and peanuts are grown in the summer season. c Socio-economic status was calculated based on ownership of eight durable goods, aggregated using principal components analysis
Summary
People have collected human waste and used the material, called night soil, to fertilize agricultural crops [1, 2]. The use of human fecal waste as an agricultural fertilizer has the potential to improve crop yields without the expense, environmental risk or transportation infrastructure required of synthetic fertilizers. High pH, desiccation and the introduction of additives such as leaf litter and ash can reduce pathogen loads in human waste products, allowing use on agricultural commodities. Helminth eggs are hardy and may require longer storage and/or higher temperatures and pH for destruction relative to other pathogens found in human stool [4]. 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
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