Objective  To study the impact of household drinking water source and toilet condition on diarrhea among children under 5 years of age and to analyze whether household drinking water and toilet sanitation conditions have joint effects on infantile diarrhea.

  Methods  The data on 4 256 children aged ≤ 5 years were extracted from the dataset of China Health and Nutrition Survey conducted between 1989 and 2015 across China. Logistic regression was used to explore the effect of household drinking water and toilet conditions and probable multiplicative interaction of the two variables on diarrheal disease among the under-5 children. The indices of interaction on an additive scale was calculated by introducing an Excel spreadsheet set up by Tomas Andersson.

  Results  Of all the infants surveyed, 248 (5.83%) were identified having diarrhea during previous four weeks. Logistic analysis demonstrated that improved household sanitation conditions of drinking water and toilet were protective factors against infantile diarrhea, with the odds ratios (95% confidence interval) of 0.59 (0.42 – 0.82) and 0.64 (0.45 – 0.91), respectively. No interactive protective effect of household drinking water and toilet sanitation conditions on infantile diarrhea was observed.

  Conclusion  Improving household sanitation is an effective way to reduce the incidence of diarrhea among under-5 children in China and protective roles of improved drinking water and toilets on diarrhea may be played through different mechanisms.