Emergency Care, Hospitalization Rates, and Floods.

Importance: Flooding is a major environmental hazard, with events increasing in intensity and frequency in the context of climate change. Floods cause significant health and economic impacts, particularly among vulnerable populations, including older adults. However, comprehensive analyses of the health consequences of flooding remain limited.

Objective: To evaluate the morbidity and health care costs among Medicare beneficiaries associated with flood exposure in the US.

Design, setting, and participants: This retrospective cohort study analyzed emergency department (ED) use and unplanned hospitalization among Medicare beneficiaries 65 years or older living in zip code tabulation areas (ZCTAs) that were exposed to large-scale flood events from January 1, 2008, to December 31, 2017. This analysis was conducted from April 3 to December 15, 2023.

Exposure: The primary exposure was the presence of a flood as recorded in the Multisourced Flood Inventories, a spatially distributed flood database.

Main outcomes and measures: A conditional fixed-effects regression approach was used to explore the incidence of all-case and cause-specific ED visits and hospitalizations before and after floods. The primary outcomes measured were the incident rate ratios (IRRs) and associated 95% CIs. Attributable risk percentages and estimated attributable excess visits were calculated. Stratified analyses were performed for evaluation of effect modification. Health care costs associated with these events were measured and standardized to 2017 US dollars.

Results: Among 11 801 527 Medicare beneficiaries 65 years or older (mean [SD] age, 74.4 [7.6] years; 56.3% female), the rate of all-cause ED visits and hospital admissions increased by 4.8% (IRR, 1.05; 95% CI, 1.04-1.05) and 7.4% (IRR, 1.07; 95% CI, 1.07-1.08) after flood exposure, respectively. The mean ZCTA-level cost was $3230 (95% CI, $3198-$3261) per ED visit and $11 310 (95% CI, $11 252-$11 367) for hospitalizations. The national costs to the Medicare system were estimated to be $69 275 429 (95% CI, $63 010 840-$76 315 210) for ED visits and $191 409 579 (95% CI, $172 782 870-$206 181 300) for hospitalizations. Stratified analyses highlighted greater impacts for certain demographic groups, including adults older than 85 years, and specific seasonal patterns.

Conclusions and relevance: In this cohort study of Medicare beneficiaries 65 years or older, flood exposure was associated with increased health care use and costs, underscoring the need for targeted public health strategies and improved disaster preparedness, especially for older adults. These findings contribute to a more comprehensive understanding of the health-related costs of flooding and can be used to inform future climate change resilience and health care planning.