Editing IPCC:AR6/WGII/Chapter-7 (section)

==== 7.2.2.2 Observed Impacts on Waterborne Diseases ====

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Important waterborne diseases (WBDs) include diarrhoeal diseases (such as cholera, shigella, cryptosporidiosis and typhoid), schistosomiasis, leptospirosis, hepatitis A and E and poliomyelitis ( [[#Cisse--2019|Cisse, 2019]] ; [[#Houéménou--2021|Houéménou et al., 2021]] ; [[#Hassan--2021|Hassan et al., 2021]] ; [[#Archer--2020|Archer et al., 2020]] ; [[#Mbereko--2020|Mbereko et al., 2020]] ; [[#Fan--2021|Fan et al., 2021]] ). The number of cases of WBDs is considerable, and even in high-income countries WBDs continue to be a concern ( [[#Cissé--2018|Cissé et al., 2018]] ; [[#Kirtman--2014|Kirtman et al., 2014]] ; [[#Levy--2018|Levy et al., 2018]] ; [[#Murphy--2014|Murphy et al., 2014]] ; [[#Brubacher--2020|Brubacher et al., 2020]] ; [[#Lee--2021|Lee et al., 2021]] ). Nevertheless, diarrhoea mortality has declined substantially since 1990, although there are variations by country, and the global burden of WBDs has decreased in line with vaccination coverage of some WBDs (such as polio and cholera), poverty reduction and improved sanitation and hygiene ( [[#Jacob--2021|Jacob and Kazaura, 2021]] ; [[#Mutono--2020|Mutono et al., 2020]] ; [[#Lee--2019|Lee et al., 2019]] ; [[#Semenza--2021|Semenza and Paz, 2021]] ; [[#Jacob--2021|Jacob and Kazaura, 2021]] ; [[#Mutono--2020|Mutono et al., 2020]] ).

Drinking water containing pathogenic microorganisms is the main driver of the burden of WBDs ( [[#Murphy--2014|Murphy et al., 2014]] ; [[#Lee--2021|Lee et al., 2021]] ; [[#Chen--2021b|Chen et al., 2021b]] ; [[#Musacchio--2021|Musacchio et al., 2021]] ). WBD outbreaks, particularly intestinal diseases, are attributable to a combination of the presence of particular pathogens (bacteria, protozoa, viruses or parasites) and the characteristics of drinking water systems in a given location ( [[#Bless--2016|Bless et al., 2016]] ; [[#Ligon--2016|Ligon and Bartram, 2016]] ; [[#Mutono--2021|Mutono et al., 2021]] ; [[#Ferreira--2021|Ferreira et al., 2021]] ).

''Since AR5 there is a growing body of evidence that increases in temperature (very high confidence), heavy rainfall (high confidence), flooding (medium confidence) and drought (low confidence) are associated with an increase of diarrhoeal diseases.'' In the majority of studies there is a significant positive association observed between WBDs and elevated temperatures, especially in areas where water, sanitation and hygiene (WASH) deficiencies are significant ( [[#Levy--2018|Levy et al., 2018]] ; [[#Carlton--2016|Carlton et al., 2016]] ; [[#Levy--2018|Levy et al., 2018]] ; [[#Sherpa--2014|Sherpa et al., 2014]] ; [[#Guzman%20Herrador--2015|Guzman Herrador et al., 2015]] ; [[#Levy--2016|Levy et al., 2016]] ; [[#Lo%20Iacono--2017|Lo Iacono et al., 2017]] ). In Ethiopia, South Africa and Senegal, increases in temperatures are associated with increases in diarrhoea, while in Ethiopia, Senegal and Mozambique, increases in monthly rainfall are associated with an increase in cases of childhood diarrhoea ( [[#Azage--2015|Azage et al., 2015]] ; [[#Thiam--2017|Thiam et al., 2017]] ; [[#Horn--2018|Horn et al., 2018]] ). Similar associations between weather and diarrhoea have been observed in Cambodia, China, Bangladesh, Pacific Island countries and the Philippines ( [[#McIver--2016a|McIver et al., 2016a]] ; [[#McIver--2016b|McIver et al., 2016b]] ; [[#Liu--2018|Liu et al., 2018]] ; [[#Wu--2014|Wu et al., 2014]] ; [[#Matsushita--2018|Matsushita et al., 2018]] ). Heavy precipitation events have been consistently associated with outbreaks of WBDs in Europe, USA, UK and Canada ( [[#Guzman%20Herrador--2015|Guzman Herrador et al., 2015]] ; [[#Levy--2016|Levy et al., 2016]] ; [[#Lo%20Iacono--2017|Lo Iacono et al., 2017]] ; [[#Curriero--2001|Curriero et al., 2001]] ; [[#Guzman%20Herrador--2016|Guzman Herrador et al., 2016]] ; [[#Levy--2018|Levy et al., 2018]] ; [[#Semenza--2021|Semenza and Paz, 2021]] ).

Impacts of floods include outbreaks of WBDs, with such events disproportionately affecting the young, elderly and immunocompromised ( [[#Suk--2020|Suk et al., 2020]] ; [[#Guzman%20Herrador--2015|Guzman Herrador et al., 2015]] ; [[#Levy--2016|Levy et al., 2016]] ; [[#Lo%20Iacono--2017|Lo Iacono et al., 2017]] ; [[#Zhang--2019a|Zhang et al., 2019a]] ). Water shortage and drought have been found associated with diarrhoeal disease peaks ( [[#Epstein--2020b|Epstein et al., 2020b]] ; [[#Subiros--2019|Subiros et al., 2019]] ; [[#Boithias--2016|Boithias et al., 2016]] ), while some reviews found insufficient evidence of the effects of drought on diarrhoea (Levy et al, 2016 ; [[#Asmall--2021|Asmall et al., 2021]] ; [[#Epstein--2020b|Epstein et al., 2020b]] ; [[#Subiros--2019|Subiros et al., 2019]] ; [[#Boithias--2016|Boithias et al., 2016]] ; [[#Ramesh--2016|Ramesh et al., 2016]] ).

''Heavy rainfall and higher than normal temperatures are associated with increased cholera risk in affected regions (very high confidence'' '').'' Cholera is an acute diarrhoeal disease typically caused by the bacterium ''Vibrio cholerae'' that can result in severe morbidity and mortality. Maximum and minimum temperatures and precipitation have been negatively associated with cholera cases. Cholera outbreaks have occurred in several regions after natural disasters, including cholera incidence increasing three-fold in El Niño-sensitive regions of Africa ( [[#Mpandeli--2018|Mpandeli et al., 2018]] ; [[#Amegah--2016|Amegah et al., 2016]] ; [[#Escobar--2015|Escobar et al., 2015]] ; [[#Jutla--2017|Jutla et al., 2017]] ; [[#Asadgol--2019|Asadgol et al., 2019]] ; [[#Moore--2018|Moore et al., 2018]] ; [[#Moore--2017|Moore et al., 2017]] ; [[#Camacho--2018|Camacho et al., 2018]] ; [[#IPCC--2019a|IPCC, 2019a]] ; Cross-Chapter Box ILLNESS in Chapter 2; Box 3.3).

''Heavy rainfall, warmer weather and drought are linked to increased risks for other GI infections (high confidence).'' As temperature increases, bacterial causes of GI infection also appear to increase, and this association is variably influenced by humidity and rainfall ( [[#Ghazani--2018|Ghazani et al., 2018]] ; [[#Levy--2016|Levy, 2016]] ). In New York it has been found that every 1°C increase in temperature was correlated with a 0.70–0.96% increase in daily hospitalisation for GI infections ( [[#Lin--2016|Lin et al., 2016]] ). In the Philippines, leptospirosis and typhoid fever showed an increase in incidence following heavy rainfall and flooding events ( [[#Matsushita--2018|Matsushita et al., 2018]] ).

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