Influence of climatic and environmental risk factors on child diarrhea and enteropathogen infection and predictions under climate change in rural Bangladesh

Abstract

AbstractBackgroundUnderstanding pathogen-specific relationships with climate is crucial to informing interventions under climate change.MethodsWe matched spatiotemporal temperature, precipitation, surface water, and humidity data to data from a trial in rural Bangladesh that measured diarrhea and enteropathogen prevalence in children 0-2 years from 2012-2016. We fit generalized additive models and estimated percent changes in prevalence using projected precipitation under Shared Socio-Economic pathways describing sustainable development (SSP1), middle of the road (SSP2), and fossil fuel development (SSP5) scenarios.FindingsAn increase from 15°C to 30°C in weekly average temperature was associated with 5.0% higher diarrhea, 6.4% higher Norovirus, and 13.0% higher STEC prevalence. Above-median precipitation was associated with 1.27-fold (95% CI 0.99, 1.61) higher diarrhea; higher Cryptosporidium, tEPEC, ST-ETEC, STEC, Shigella, EAEC, Campylobacter, Aeromonas, and Adenovirus 40/41; and lower aEPEC, Giardia, Sapovirus, and Norovirus prevalence. Other associations were weak or null. Compared to the study period, diarrhea prevalence was similar under SSP1 (7%), 3.4% (2.7%, 4.3%) higher under SSP2, and 5.7% (4.4%, 7.0%) higher under SSP5. Prevalence of pathogens responsible for a large share of moderate-to-severe diarrhea in this setting (Shigella, Aeromonas) were 13-20% higher under SSP2 and SSP5.InterpretationHigher temperatures and precipitation were associated with higher prevalence of diarrhea and multiple enteropathogens; higher precipitation was associated with lower prevalence of some enteric viruses. Under likely climate change scenarios, we projected increased prevalence of diarrhea and enteropathogens responsible for clinical illness. Our findings inform pathogen-specific adaptation and mitigation strategies and priorities for vaccine development.FundingBill & Melinda Gates Foundation, National Institute of Allergy and Infectious Diseases, National Heart, Lung, And Blood Institute, Stanford University School of Medicine, Chan Zuckerberg BiohubResearch in ContextEvidence before this studyWe searched Google Scholar and Scopus for studies published from January 1, 2000 to present using the following three queries: 1) child; and diarrhea OR “enteric infection”; and meteorological OR environmental OR “surface water” OR “standing water”; and risk AND/OR factors; 2) Climate AND change AND project* AND diarrhea OR diarrhoea; 3) climate AND change AND project* OR model AND enter* AND infect* AND E. coli. Studies generally focused on individual risk factors for diarrhea transmission or enteric infection, with an emphasis on temperature and precipitation. Studies found that higher temperatures were associated with higher incidence of bacterial diarrhea and lower incidence of viral diarrhea; few studies have investigated associations between temperature and parasitic diarrhea. Heavy rainfall, particularly after dry periods, was associated with higher diarrhea prevalence, though heavy rainfall during rainy seasons was found to protect against diarrhea incidence. Similarly, flooding of surface water and shallow wells was also associated with higher diarrhea prevalence. Very few studies investigated associations between diarrhea or enteropathogen carriage and surface water presence, or humidity. A recent individual participant meta-analysis of studies in 19 low- and middle-income countries found that higher precipitation was associated with a small decrease in enterotoxigenic E. coli (ETEC) and Campylobacter spp. prevalence and no difference in Shigella, Cryptosporidium, or Giardia, or enteric virus prevalence. Weekly average temperature increases of 10-40° C within the study period were associated with higher risk of Campylobacter, ETEC, Shigella, Cryptosporidium, Giardia, and adenovirus, and lower risk of sapovirus and rotavirus, and generally, associations were stronger. Higher humidity was associated with higher risk of enteric bacterial infections and lower risk of enteric virus infection. A small number of studies have projected diarrhea under climate change in low- and middle-income countries. Studies have estimated a 15-20% increase in global diarrhea risk in 2040-2069 relative to 1961-1990, up to 21% increase in diarrhea incidence in northern India from 2013 to the 2040s, 3-10% increase in diarrhea cases in the Gaza Strip associated with 1.5° to 2°C increases in temperature, and an 8% increase in diarrhea burden by 2050 in Nepal. One study estimated an additional 1,625,073 ETEC diarrhea cases in Bangladesh from 2046-2065 due to climate change. No studies estimated changes in the presence of multiple enteropathogens under possible climate change scenarios.Added value of this studyThis study matched remote sensing data on precipitation, temperature, surface water, and humidity to data on diarrhea and enteropathogen carriage in children under 2 years from a trial in rural Bangladesh. We fit flexible models to investigate potentially non-linear relationships between each climate and environmental risk factor and each health outcome. In addition, we predicted the prevalence of each outcome under three possible climate change scenarios. Our predictions leveraged the spatiotemporal distributions of both climate precipitation projections and diarrhea and enteropathogen carriage in the trial. To our knowledge, this is the first study to predict prevalence under climate change scenarios for both diarrhea and multiple enteropathogens in a rural, low-resource south Asian setting. Our study sheds light on how climate change may impact diarrhea and enteropathogen carriage in Bangladesh, which is highly vulnerable to climate change due to its low altitude and seasonal flooding.Implications of all the available evidenceWe found that both higher temperatures and precipitation were associated with higher diarrhea prevalence, consistent with prior studies. Compared to prior studies, which have primarily found associations between diarrhea and heavy rainfall following a dry period, we found that moderate levels of weekly precipitation were associated with higher diarrhea prevalence. Relationships between climatic and environmental variables and enteropathogen carriage varied by taxa, as other studies have found, but for some pathogens and risk factors, we observed associations in different directions than prior studies. Under middle of the road and fossil fuel-based development climate change scenarios, we projected increased diarrhea prevalence and taxa-specific changes in enteropathogen prevalence. Our findings suggest that climate change may exacerbate diarrhea burden in rural Bangladesh in the absence of sustainable development and inform prioritization of pathogen-specific mitigation and/or adaptation interventions (e.g., vaccines) for young children in rural, South Asian settings under climate change.