Hands play a major role especially in the transmission of blood-borne, fecal, and respiratory tract viruses.
Hand washing after use of bathroom aims at preventing the transmission of pathogens, which rely on faecal-oral transmission, such as rotavirus, noroviruses, enteroviruses in some cases hepatitis A virus (1). It prevents those pathogens from reaching the kitchen for example where it could lead to subsequent ingestion.
Recently a systematic review (2) identified a total of 2881 unique publications addressing this question.
Interestingly, this study found a varying prevalence of hand-washing after contact with extcreta:
We estimate that 19% of people worldwide wash their hands with soap
after contact with excreta. The regional mean prevalence of
handwashing with soap ranges between 13% and 17% in low- and
middle-income regions, and between 42% and 49% in high-income regions
However, the authors reported a 40% reduction in the risk of diarrhoea from the promotion of handwashing with soap (RR 0.60, 95% CI 0.53–0.68) suggesting that hand-washing impact on faecal oral transmission and reduces risk of diarrhoea.
Kampf G, Kramer A. Epidemiologic Background of Hand Hygiene and Evaluation of the Most Important Agents for Scrubs and Rubs. Clinical Microbiology Reviews. 2004;17(4):863-893.
Freeman et al. Systematic review: Hygiene and health: systematic review of handwashing practices worldwide and update of health effects. Tropical Medicine and international health. Volume 19, Issue 8. August 2014. Pages 906–916