Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA.
Department of Epidemiology, University of Michigan-Ann Arbor, Ann Arbor, Michigan, USA.
Environ Health Perspect. 2020 Dec;128(12):126001. doi: 10.1289/EHP6181. Epub 2020 Dec 7.
Projected increases in extreme weather may change relationships between rain-related climate exposures and diarrheal disease. Whether rainfall increases or decreases diarrhea rates is unclear based on prior literature. The concentration-dilution hypothesis suggests that these conflicting results are explained by the background level of rain: Rainfall following dry periods can flush pathogens into surface water, increasing diarrhea incidence, whereas rainfall following wet periods can dilute pathogen concentrations in surface water, thereby decreasing diarrhea incidence.
In this analysis, we explored the extent to which the concentration-dilution hypothesis is supported by published literature.
To this end, we conducted a systematic search for articles assessing the relationship between rain, extreme rain, flood, drought, and season (rainy vs. dry) and diarrheal illness.
A total of 111 articles met our inclusion criteria. Overall, the literature largely supports the concentration-dilution hypothesis. In particular, extreme rain was associated with increased diarrhea when it followed a dry period [incidence rate ratio ; 95% confidence interval (CI): 1.05, 1.51], with a tendency toward an inverse association for extreme rain following wet periods, albeit nonsignificant, with one of four relevant studies showing a significant inverse association (; 95% CI: 0.771, 1.08). Incidences of bacterial and parasitic diarrhea were more common during rainy seasons, providing pathogen-specific support for a concentration mechanism, but rotavirus diarrhea showed the opposite association. Information on timing of cases within the rainy season (e.g., early vs. late) was lacking, limiting further analysis. We did not find a linear association between nonextreme rain exposures and diarrheal disease, but several studies found a nonlinear association with low and high rain both being associated with diarrhea.
Our meta-analysis suggests that the effect of rainfall depends on the antecedent conditions. Future studies should use standard, clearly defined exposure variables to strengthen understanding of the relationship between rainfall and diarrheal illness. https://doi.org/10.1289/EHP6181.
预计极端天气的增加可能会改变与降雨相关的气候暴露和腹泻病之间的关系。根据以往的文献，降雨是增加还是减少腹泻率尚不清楚。浓缩稀释假说表明，这些相互矛盾的结果可以用背景降雨水平来解释：在干旱期之后的降雨可以将病原体冲入地表水，从而增加腹泻的发病率，而在潮湿期之后的降雨可以稀释地表水的病原体浓度，从而降低腹泻的发病率。
在本分析中，我们探讨了发表文献在多大程度上支持浓缩稀释假说。
为此，我们对评估降雨、极端降雨、洪水、干旱和季节（雨季与旱季）与腹泻病之间关系的文章进行了系统搜索。
共有 111 篇文章符合我们的纳入标准。总的来说，文献在很大程度上支持浓缩稀释假说。特别是，在干旱期之后的极端降雨与腹泻增加有关[发病率比；95%置信区间（CI）：1.05，1.51]，尽管没有统计学意义，但在潮湿期之后的极端降雨与腹泻呈负相关趋势，四项相关研究中有一项显示出显著的负相关[95% CI：0.771，1.08]。细菌性和寄生虫性腹泻在雨季更为常见，为浓缩机制提供了病原体特异性支持，但轮状病毒腹泻则呈现相反的关联。关于雨季内病例发生时间（例如早期与晚期）的信息缺乏，限制了进一步分析。我们没有发现非极端降雨暴露与腹泻病之间存在线性关联，但有几项研究发现与低降雨和高降雨均与腹泻有关的非线性关联。
我们的荟萃分析表明，降雨的影响取决于先前的条件。未来的研究应使用标准、明确界定的暴露变量，以加强对降雨与腹泻病之间关系的理解。https://doi.org/10.1289/EHP6181.
