Abstract

Background:

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.

Objectives:

In this analysis, we explored the extent to which the concentration-dilution hypothesis is supported by published literature.

Methods:

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.

Results:

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 $\left(\text{IRR}\right)=1.26$; 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 ($\text{IRR}=0.911$; 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.

Discussion:

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

中文翻译：

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了解降雨对腹泻的影响：使用系统评价和荟萃分析检验浓度稀释假说

摘要

背景：

预计极端天气的增加可能会改变与降雨相关的气候暴露与腹泻病之间的关系。根据先前的文献，降雨是否会增加或减少腹泻率尚不清楚。浓度稀释假说表明，这些相互矛盾的结果可以通过降雨的背景水平来解释：干旱期后的降雨可以将病原体冲入地表水中，增加腹泻发病率，而潮湿期后的降雨可以稀释地表水中的病原体浓度，从而减少腹泻发生率。

目标：

在这项分析中，我们探讨了已发表文献对浓度稀释假说的支持程度。

方法：

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）与腹泻疾病之间关系的文章进行了系统搜索。

结果：

共有 111 篇文章符合我们的纳入标准。总体而言，文献很大程度上支持浓度稀释假说。特别是，在干旱期之后，极端降雨与腹泻增加有关[发病率比$（\text{内部收益率}）=1.26$; 95% 置信区间 (CI)：1.05, 1.51]，尽管不显着，但雨季后的极端降雨有呈负相关的趋势，四项相关研究之一显示了显着的负相关（$\text{内部收益率}=0.911$; 95% CI: 0.771, 1.08)。细菌性和寄生虫性腹泻的发病率在雨季更为常见，这为集中机制提供了病原体特异性支持，但轮状病毒腹泻却表现出相反的关联。缺乏有关雨季内病例发生时间（例如早与晚）的信息，限制了进一步的分析。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，但一些研究发现低雨和高雨均与腹泻相关，存在非线性关联。

讨论：

我们的荟萃分析表明，降雨的影响取决于前期条件。未来的研究应使用标准的、明确定义的暴露变量来加强对降雨与腹泻病之间关系的理解。https://doi.org/10.1289/EHP6181