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1/ Why do many WASH interventions have limited effects on child stunting? Our historical data suggest something surprising: Sanitation infrastructure alone often wasn’t enough, even in the past. New BMJ Global Health paper 👇 doi.org/10.1136/bmjg...

2/ Poor water, sanitation and hygiene (WASH) are widely seen as drivers of child stunting. Repeated exposure to faecal pathogens → diarrhoeal disease → impaired nutrient absorption → slower growth. So improving sanitation should reduce stunting. But the evidence is mixed.

3/ Recent large trials (e.g. WASH Benefits, SHINE) found limited impacts on child linear growth despite major investments in sanitation infrastructure. Our historical data suggest this puzzle isn’t new. We see similar patterns in the past.

4/ Take 19th-century England. Cities invested massively in sanitation and clean water. The results were dramatic: • cholera epidemics were eliminated • under-5 typhoid mortality fell by ~88% Yet child stunting remained above 40% in the 1890s.

5/ Why? Because building sanitation infrastructure doesn’t necessarily reduce children’s exposure to all faecal pathogens. Exposure pathways also depend on: • hygiene behaviour • infant feeding practices • environmental contamination (e.g. horse manure)

6/ In Britain, diarrhoeal disease remained widespread and only declined decades after the introduction of clean water and sanitation. Declining diarrhoeal disease caused by: • improved hygiene behaviour • safer infant feeding • environmental changes (fewer horses in cities)

7/ This is why infrastructure alone often had limited effects on stunting. Behaviour and environmental change also mattered.

8/ Now compare to early-20th-century Jamaica. A Rockefeller Foundation hookworm campaign combined: • treatment • improved latrines • intensive hygiene education Campaign workers even brought microscopes into villages so people could see hookworm parasites.

9/ The result? Communities began building improved latrines themselves and sanitary behaviour changed widely. Infant mortality fell by 41% in the 1920s–30s. Similar sanitation challenge—very different outcome. See great paper by Preyer and Strobl: ehes.org/wp-content/u...

11/ So why is changing WASH behaviour so difficult today? We speculate that high levels of child mortality in the past provided very strong incentives for people to adopt better WASH behaviours. However, child mortality is far lower today, weakening these incentives.

12/ Child stunting is not as salient as mortality as a health indicator because it is difficult for individuals to understand. Stunted children look normal relative to their peers in LMICs. They are only short compared to healthy children, which people cannot observe.