A Secondary Sanitary Revolution? What About the First One?

Water and sanitation is being taken increasingly seriously in Low- and Middle-Income Countries (LMICs). This is a good thing because, despite improved treatment of diarrhoea and vaccination against rotavirus,[1] gastrointestinal diseases are one of the two biggest causes of death in children under the age of five.[2] Yet recent evaluations of water and sanitation interventions show patchy results [3] and are overall disappointing.[4] [5] Very few studies have been done in urban areas, but infant death rates in slums are unconscionably high.[6]

Why are water and sanitation interventions so disappointing in the LMICs of today when the Sanitary Revolution around the turn of the 19th century was so successful? Well it turns out that the Sanitary Revolution was a bit of a myth – Thomas McKeown, Professor of Social Medicine at the University of Birmingham, caused quite a stir by pointing this out in the 1970s.[7] The ‘historical epidemiology’ of this time period is intensely interesting. While sequential chlorination of water in North American cities in the early years of the 1900s was associated with corresponding dramatic drops in the incidence of typhoid fever,[8] establishment of water and sanitation in the Netherlands [9] and Estonia [10] produced no benefit whatsoever on gastrointestinal deaths. Only one-third of the reduction in gastrointestinal-related deaths observed in around the turn of the 18th century Germany could be attributed to water and sanitation improvements.[9]
So why do water and sanitation interventions produce such variable, and often disappointing, benefits? In rural India this can often be attributed to low use of facilities, but little or no health benefit has been observed, even when uptake has been high. A number of (non-exclusive) theories can be adduced:

1) The inadequate dose theory. This holds that the type of intervention deployed in LMICs has generally been inadequate. For example, pit latrines (classed as ‘improved sewerage’ by the UN) do not clean up the environment adequately.[11] Similarly, water pipes may be installed, but the water may be contaminated en route.[12] St Petersburg is a notorious example.

2) The tipping point theory. This theory is an elaboration of the above inadequate dose theory and postulates a non-linear relationship between the intensity, type of water and sanitation (facility), and coverage of interventions and health, with increasing and then decreasing returns to scale as shown in Figure 1. By this theory, many interventions (such as pit latrines) simply fail to reach the ‘tipping point’, especially in densely inhabited city areas.

085 DCB A Secondary Sanitary Revolution Fig 1

3) The deep contamination theory (Figure 2). By this theory contamination follows many routes and becomes embedded in local communities, with transmission routes that are frequently replenished, so that garbage dumps, flies, nappies, soil and the human gut all act as repositories of infection. Food may be contaminated along its supply chain, as well as in preparation. Floods sweep sewage out of drains and back into communities. Cleaning up such an environment moves the tipping point (shown in Figure 1) to the right (meaning it is harder to reach) and may also take time to effect – a point to which we return.


4) The multiple agent hypothesis. By this theory some germs are more easily eradicated than others. Typhoid is waterborne, but, unlike cholera, it cannot replicate in water. Ensuring uncontaminated water may be enough to eradicate this particular problem. However, hookworms are at the other end of the spectrum, since they can be carried asymptomatically and linger in soil. There is even some evidence that organisms gain virulence as they are passed rapidly from host to host.[13] So this theory predicts that some types of infection might decrease more rapidly than others in response to an intervention. Moreover, some real gains, with respect to some type of serious infection, might be obscured by little or no change in more common, but less serious infections.

5) The multiple causes theory. This theory relies on evidence that malnutrition and gastrointestinal infections are self-reinforcing. Certainly malnutrition is associated with an altered microbiome, which, in turn, reduces absorption of food, creating a vicious cycle.[14] The microbiome affects the immune system, which, in turn, affects resistance to infection.

6) The ‘double-handed’ hygiene hypothesis. Hygiene can compensate for dirty water and a contaminated environment, and some of the most consistently effective interventions in LMICs have been based on improved hygiene and near use decontamination.[4] [15] On the other hand, hygiene does not seem important in places where exposure to harmful pathogens is low and, in such circumstances, hygiene may be too fastidious, leading to allergic illnesses.

7) The insensitive outcome hypothesis. Measuring the health benefit of sanitation is not unproblematic – the standard question on diarrhoea enquires about loose stools over a three-day period, and the measurement error appears to be large.[16] An account of blood in stools, signifying dysentery (Shigella and amoeba) is more specific, but is much rarer, leading to imprecision (lack of statistical power). Anthropological measurements reflect long-term conditions, and many factors, including gastrointestinal infections and malnutrition (see above), and also age of weaning, birth weight, and mother’s weight (inter-generational effects). We are working on designing a better (equally sensitive, but more specific and less reactive) method to measure gastrointestinal health.[17]

There may well be an element of truth in all these hypotheses. If a fully functioning water and sewerage system was installed, lanes paved and drained, and garbage eliminated, then there would probably be an impressive and rapid improvement in gastrointestinal health, especially if malnutrition was also tackled. But the same water and sewerage system would probably have moderate and delayed benefits if not accompanied by the other measures mentioned. What nutrition and vaccination would achieve without water and sanitation is unknown, but as they are less expensive, the experiment should be tried in places where water and sanitation improvements are some time away. In-depth study of transmission routes will help explicate some of the other theories postulated and careful comparative studies will help identify the tipping point for the most cost-effective solutions. What is for sure is that science has a role to play in unravelling the process by which we may achieve a Second Sanitary Revolution.

— Richard Lilford, CLAHRC WM Director


  1. GBD Diarrhoeal Diseases Collaborators. Estimates of global, regional, and national morbidity, mortality, and aetiologies of diarrhoeal diseases: a systematic analysis for the Global Burden of Disease Study 2015. Lancet Infect Dis. 2017; 17: 909-48.
  2. Global Burden of Disease Pediatrics Collaboration. Global and National Burden of Diseases and Injuries Among Children and Adolescents Between 1990 and 2013. JAMA Pediatr. 2016; 170(3): 267-87.
  3. Lilford RJ, Oyebode O, Satterthwaite D, et al. Improving the health and welfare of people who live in slums. Lancet. 2017; 389: 559-70.
  4. Wolf J, Prüss-Ustün A, Cumming O, et al. Assessing the impact of drinking water and sanitation on diarrhoeal disease in low- and middle-income settings: systematic review and meta-regression. Trop Med Int Health. 2014; 19(8): 928-42.
  5. Fuller JA, Westphal JA, Kenney B, Eisenberg JNS. The joint effects of water and sanitation on diarrhoeal disease: a multicountry analysis of the Demographic and Health Surveys. Trop Med Int Health. 2015; 20(3): 284-92.
  6. Feikin DR, Olack B, Bigogo GM, et al. The burden of common infectious disease syndromes at the clinic and household level from population-based surveillance in rural and urban Kenya. PLoS One. 2011; 6: e16085.
  7. McKeown T, Record RG, Turner RD. An interpretation of the decline of mortality in England and Wales during the twentieth century. Popul Stud. 1975. 29(3): 391-422.
  8. Cutler D & Miller G. The Role of Public Health Improvements in Health Advances: The 20th Century United States. NBER Working Paper 10511. Cambridge, MA: National Bureau of Economic Research; 2004.
  9. Van Poppel F & van der Heijden C. The effects of water supply on infant and childhood mortality: a review of historical evidence. Health Trans Rev. 1997; 7(2): 113-48.
  10. Jaadla H & Puur A. The impact of water supply and sanitation on infant mortality: Individual-level evidence from Tartu, Estonia, 1897-1900. Popul Stud. 2016; 70(2): 163-79.
  11. Nakagiri A, Niwagaba CB, Nyenje PM, Kulabako RN, Tumuhairwe JB, Kansiime F. Are pit latrines in urban areas of sub-Saharan Africa performing? A review of usage, filling, insects and odour nuisances. BMC Public Health. 2016; 16: 120.
  12. Eschol J, Mahapatra P, Keshapagu S. Is fecal contamination of drinking water after collection associated with household water handling and hygiene practices? A study of urban slum households in Hyderabad, India. J Water Health. 2009; 7(1): 145-54.
  13. Ewald PW. Waterborne transmission and the evolution of virulence among gastrointestinal bacteria. Epidemiol Infect. 1991; 106: 83-119.
  14. Rook G, Bäckhed F, Levin BR, McFall-Ngai MJ, McLean AR. Evolution, human-microbe interactions, and life history plasticity. Lancet. 2017; 390: 521-30.
  15. Freeman MC, Garn JV, Sclar GD, Boisson S. The impact of sanitation on infectious disease and nutritional status: A systematic review and meta-analysis. Int J Hyg Environ Health. 2017; 220(6): 928-49.
  16. Schmidt WP, Arnold BF, Boisson S, et al. Epidemiological methods in diarrhoea studies – an update. Int J Epidemiol. 2011; 40(6): 1678-92.
  17. Lilford RJ. Protocol to Test Hypothesis That Streptococcal Infections and Their Sequelae Have Risen in Incidence Over the Last 14 Years in England. NIHR CLAHRC West Midlands News Blog. 13 January 2017.

3 thoughts on “A Secondary Sanitary Revolution? What About the First One?”

  1. The “hoary chestnut” of our sanitary habits and the vague relationship between “constipation” and Western Diseases, is significant and true. 20-30% Western populations “strain” to initiate or complete defaecation (Heaton, 1991). 1% of the population only achieve defaecation once per week, 0.1% once per month !! (Heaton, 1991). Physical efforts during defaecation injure autonomic nerves at different anatomical sites (mouth open or mouth closed). If you are a bottle-fed infant in the supine position you injure coeliac nerves (causing T1DM, Mundinger, 2016) or cardiac nerves (asthma). If you are an adult then stage 4, nulliparous endometriosis and chronic prostate ”tis are the inexorable outcomes. There are many descriptions of colectomy “curing” diseases (Sur WA Lane, 1924) and DP Burkitt observations from 1973 are pertinent – squatting prevents straining.

    The key outcome is that autonomic denervation carries diverse and varying consequences that produce different manifestations of many Western diseases (Quinn, 2014). These range from tissue hyperplasia in adenomyosis and leiomyoma, opportunist infection in preterm labour, viscerovisceral reflexes in preeclampsia, pain in endometriosis, impaired visceral and ducal motility in appendicitis and cholecystitis, etc etc,

    The message is simply touch your toes (squat) on contemporary sanitary arrangements (Thomas Crapper, 1861 et seq) and wait for things to happen (anorectal reflex is usually intact and effective !),

  2. One astonishing thing is the enormous and egregious spike in diarrhoea deaths in India and Nigeria – so far above the other LMICs that it seems to me that the rapid urbanisation and mixing of cultures from different areas and has to be a factor in these two changing economies. Perhaps the cheaper option of factor 6 awareness programmes – wash your hands properly – is something that should be done anyway regardless of whether rubbish collection and good nutrition can be afforded (and without stopping anyone from squatting as MJQuinn discusses above).

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