Atlantic Basin Tropical Cyclones and Associated Risks of Mortality and Emergency Medicare Hospitalizations in the United States

Background. The East and Gulf Coasts of the United States (US) are frequently exposed to powerful and destructive hurricanes and other tropical cyclones, and the intensity of tropical cyclones in the Atlantic basin may increase under climate change. To date, most death and injury tolls from these storms have been estimated using a traditional disaster surveillance approach, where each death or injury is considered case-by-case to determine if it can be attributed to the storm. This approach may not always capture the overall community-wide health effects associated with storm exposure, especially in cases where much of the excess morbidity and mortality result from outcomes common outside of disaster periods (e.g., heart attacks, respiratory problems) rather than well-characterized storm-related risks rarer outside of storm events (e.g., drowning, carbon monoxide poisoning). Here, we conducted the first multi-year, multi-state epidemiological study to estimate the relative risks (RRs) of storm exposures on the community-wide health outcomes of mortality and Medicare hospitalizations in a large number of eastern US communities.

Methods. To measure storm exposure, we separately considered five metrics—distance to storm track; cumulative rainfall; maximum sustained wind speed; flooding; and tornadoes. Our meteorological data were mainly based on the NASA’s North American Land Data Assimilation System Phase 2 (NLDAS-2) meteorological forcing dataset and the NOAA’s Storm Event Database. For mortality outcomes, we used community vital records for 78 large eastern US communities, 1988–2005, to estimate the risks of storm exposure on all-cause, cardiovascular, respiratory, and accidental mortality. For emergency hospitalization outcomes, we used Medicare claims for 180 eastern US counties, 1999–2010, to estimate storm-related risks on emergency hospitalizations from cardiovascular and respiratory disease among Medicare beneficiaries, all aged 65 years or older. We estimated how health outcome rates across the study population (all community residents for the mortality analysis; community Medicare beneficiaries for the hospitalization analysis) differed during tropical cyclone exposures compared to what would have been expected had the storms not occurred, using a matched analysis to compare health risks on storm-exposed days versus similar unexposed days within each community. For each combination of exposure metric and health outcome, we estimated storm-associated health risks for a window from two days before to seven days after the day of storm’s closest approach.

Results. For the mortality analysis (1988–2005), 92 Atlantic Basin tropical cyclones were considered based on US landfall or close approach, with 70 communities exposed to at least one storm; for the hospitalization analysis (1999–2010), 74 storms were considered for 174 exposed counties. Under the wind-based exposure metric, we found substantially elevated risk for all mortality outcomes considered compared with similar unexposed days, with risk typically highest on the day of the storm’s closest approach. For the strongest wind exposures, cumulative RRs of mortality during the full storm exposure window were 1.90 (95% confidence interval (CI): 1.58, 2.29), 161.41 (61.62, 422.80), 1.30 (0.97, 1.76), and 1.54 (0.70, 3.39) for all-cause, accidental, cardiovascular, and respiratory mortality, respectively. When excluding the ten most severe storm events based on wind exposures, however, we did not observe significantly increased risk for the remaining tropical cyclones on any mortality outcomes. Among Medicare beneficiaries, the risks of emergency hospitalizations generally decreased on the day of the storm’s closest approach compared to expected rates had the storm not occurred and then significantly increased on the following one or two days, with particularly clear evidence of a storm-related increase in risk of respiratory hospitalizations. Cumulative risks of respiratory hospitalizations were increased under all storm exposure metrics considered, for all storms and across all exposed counties; these risks remained significantly elevated (RR = 2.22, 95% CI, 1.53 to 3.21) even when the ten most severe storm events (based on wind exposure) were excluded.

Conclusions. Severe tropical cyclone exposures can have important health impacts beyond direct accidental deaths and injuries, including potentially important risks for cardiovascular and respiratory mortality and for respiratory Medicare hospitalizations. While most storms with high associated risks of non-accidental mortality were characterized by very high wind exposures, storms with a wider range of exposure characteristics were associated with increased risk of respiratory Medicare hospitalizations. For mortality outcomes, the highest storm-related risks were observed on the day of the storm’s closest approach, while the observed increased risk of emergency Medicare respiratory hospitalizations typically followed the storm by one or two days. Our findings complement existing literature based on surveillance methods by quantifying community-wide adverse health risks associated with tropical cyclone exposures, especially for several common causes of mortality and morbidity that are difficult to attribute as storm-related on a case-by-case basis.