The Complex Epidemiological Relationship between Flooding Events and Human Outbreaks of Mosquito-Borne Diseases: A Scoping Review

Abstract

Background: Climate change is expected to increase the frequency of flooding events. Although rainfall is highly correlated with mosquito-borne diseases (MBD) in humans, less research focuses on understanding the impact of flooding events on disease incidence. This lack of research presents a significant gap in climate change-driven disease forecasting.

Objectives: We conducted a scoping review to assess the strength of evidence regarding the potential relationship between flooding and MBD and to determine knowledge gaps.

Methods: PubMed, Embase, and Web of Science were searched through 31 December 2020 and supplemented with review of citations in relevant publications. Studies on rainfall were included only if the operationalization allowed for distinction of unusually heavy rainfall events. Data were abstracted by disease (dengue, malaria, or other) and stratified by post-event timing of disease assessment. Studies that conducted statistical testing were summarized in detail.

Results: From 3,008 initial results, we included 131 relevant studies (dengue $n=45$, malaria $n=61$, other MBD $n=49$). Dengue studies indicated short-term ($<1\text{month}$) decreases and subsequent (1-4 month) increases in incidence. Malaria studies indicated post-event incidence increases, but the results were mixed, and the temporal pattern was less clear. Statistical evidence was limited for other MBD, though findings suggest that human outbreaks of Murray Valley encephalitis, Ross River virus, Barmah Forest virus, Rift Valley fever, and Japanese encephalitis may follow flooding.

Discussion: Flooding is generally associated with increased incidence of MBD, potentially following a brief decrease in incidence for some diseases. Methodological inconsistencies significantly limit direct comparison and generalizability of study results. Regions with established MBD and weather surveillance should be leveraged to conduct multisite research to a) standardize the quantification of relevant flooding, b) study nonlinear relationships between rainfall and disease, c) report outcomes at multiple lag periods, and d) investigate interacting factors that modify the likelihood and severity of outbreaks across different settings. https://doi.org/10.1289/EHP8887.

Figure 1.

Hypothesized conceptual diagram of key factors that link flooding and human mosquito-borne disease frequency.

Figure 2.

PRISMA 2009 flow diagram for the scoping review of flood and mosquito-borne disease (From Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PloS Med 6(7):e1000097. Doi:10.1371/journal.pmed1000097). Note: See Excel Table S1 for a detailed list of reasons for exclusion.

Figure 3.

Number of studies on flood and mosquito-borne disease occurrence by country as (A) total, (B) dengue, (C) malaria, and (D) studies with statistical hypothesis testing of the association between flood and mosquito-borne disease (see Excel Table S10 for data).

Figure 3.

Number of studies on flood and mosquito-borne disease occurrence by country as (A) total, (B) dengue, (C) malaria, and (D) studies with statistical hypothesis testing of the association between flood and mosquito-borne disease (see Excel Table S10 for data).