210-Day Flood Health Risks: What Doctors Must Know
Flood exposure is linked to increased risks for hospitalisation for all causes and for 10 specific conditions, with relative risks ranging from 1.11 to 1.61 and persisting for up to 210 days.
An analysis of 300 million hospitalisation records from 747 communities in eight countries and territories showed that floods accounted for as much as 0.27% of all-cause admissions.
Background
Floods are the most frequent natural disaster, with approximately 23% of the global population exposed to floods with depths > 0.15 m during once-in-100-year flood events.
Projections indicate that the severity, duration, and frequency of floods will escalate due to increasingly frequent extreme precipitation events and rising sea levels caused by global warming.
In addition to the direct health impacts caused by the physical force of floods or related accidents, emerging evidence suggests that flooding may have broad indirect effects on human health.
Current epidemiologic studies on flood-related health impacts focus primarily on disease incidence, mainly digestive diseases, infectious diseases, and mental disorders.
Understanding the impact of flooding on hospitalisation risk is crucial for healthcare providers to prepare for increased demand following such events.
METHODOLOGY:
Researchers examined daily hospitalisation data from 2000 to 2019 in 747 communities across Australia, Brazil, Canada, Chile, New Zealand, Taiwan, Thailand, and Vietnam, averaging 13 years of follow-up per community.
The analysis included 300 million hospitalisation records, with a flood day defined as any day from the beginning to the end of flood events in each community.
Associations between flood days and daily hospitalisation risks were estimated using a quasi-Poisson regression model with a non-linear distributed lag function, followed by a random-effects meta-analysis.
TAKEAWAY:
The cumulative relative risks [RRs] of hospitalisation after flood exposure were 1.26 (95% CI, 1.15-1.38) for all causes, 1.35 (95% CI, 1.21-1.5) for cardiovascular diseases, and 1.61 (95% CI, 1.39-1.86) for diabetes.
Associations were modified by climate type, flood severity, age, population density, and socio-economic status, with stronger effects observed in communities with higher population density or higher socio-economic status.
Flood exposure contributed to up to 0.27% of all-cause hospitalisations, 0.41% of cardiovascular disease hospitalisations, and 1.93% of diabetes admissions.
Health impacts persisted for up to 210 days after exposure ended, except for infectious diseases (90 days) and mental disorders (150 days).
IN PRACTICE:
'Health service providers should anticipate increased health risks during and after floods and prepare for the heightened service demands, possibly through strengthening capacities in medical supplies, human resource management, and triage strategy. Public health institutions should closely monitor the reasons for hospitalisation after floods as a method for disease control and efficient resource allocation in the aftermath of floods. Policymakers should prioritise enhancing health system resilience to natural disasters, recognising that overwhelmed health systems after floods can lead to severe disease burden and even avoidable deaths,' the study authors wrote.
SOURCE:
The study was led by Yuming Guo, PhD, and Shanshan Li, PhD, of the Climate Air Quality Research Unit, School of Public Health and Preventive Medicine, Monash University in Melbourne, Australia, and included Paulo Saldiva, MD, PhD, of the Department of Pathology, School of Medicine, University of São Paulo in São Paulo, Brazil, and was published online on April 08, 2025, in Nature Water.
LIMITATIONS:
The Dartmouth Flood Observatory dataset, which primarily checks events mentioned in news reports, may under-represent flooding, particularly in South America. The exposure assessment was conducted at the community level rather than at the individual level, as the exact residential addresses were kept confidential. Similarly, a community may have both flooded and non-flooded areas, which has the potential to lead to underestimation of risk.
DISCLOSURES:
The study was supported by the Australian Research Council, Australian National Health and Medical Research Council, and National Research Council of Thailand. The funders had no role in the study design, collection, analysis, and interpretation of data, writing of the report, or the decision to submit the paper for publication.
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