Assessing the Health Impacts of Hurricanes and Tropical Storms in Florida: Methodological Challenges and Solutions

Background: The overarching goal of the Florida Building Resilience Against Climate Effects Program is to increase resilience to the health effects of weather variability by incorporating the best available climate science into routine public health practice. Part of this mandate is to understand the current state-level impacts of extreme weather on the health of Floridians. Because of our unique peninsular geography, extensive coast line, and exposure to both the Atlantic Ocean and Gulf of Mexico, Florida experiences more hurricane and tropical storm landfalls than any other state. Tropical cyclones (TCs) produce a wide variety of impacts (storm surge, inland flooding, high winds, tornadoes), which may have a broad range of effects on human health. Most literature in this area focuses on trauma (e.g., injury and drowning) and mental health issues (e.g., stress and anxiety). These studies have typically been limited to one event (e.g., Hurricane Katrina) and a small geographic area (e.g., the Mississippi Delta). Depending on the size and strength of the system, inland areas - even those outside of the main storm track - may experience as much damage as coastal areas. Because of this, our objective was to take a more comprehensive look at the impact of these systems on human health in Florida. Here, we describe the methodological challenges and solutions employed in analyzing the impacts of TCs on one human health concern: mental health emergency department (ED) visits.

Methods: The Southeast Regional Climate Center provided maximum wind speeds observed in each Florida county for each TC from 2005 through 2011. Only counties experiencing tropical storm-force (39-74 MPH) or hurricane-force (≥ 74 MPH) winds were included. During this period, there were two hurricanes and ten tropical storms affecting 66 of Florida's 67 counties.

The Florida Agency for Health Care Administration has been collecting ED data since 2005 from all hospitals statewide. We used primary diagnosis codes to define ED visits related to mental health conditions: stress, depression, substance-related conditions, neuroses, organic psychotic conditions, other psychotic conditions, and all mental health conditions combined.

We chose to conduct a hybrid matched cohort study where our unit of analysis was daily counts of ED visits in a specific county, comparing impact to control periods. For mental health conditions, the impact period included both a pre- and post-landfall timeframe (-2 to 30 days) to include the stress and anxiety associated with impending danger, as well as mental health effects associated with loss of property, displacement, injury, and death of loved ones. The choice of control periods is crucial in matched study designs, and we considered two separate classifications. First, we matched control to impact periods based on climatological factors, using the same time period in other years with similar climatological characteristics (e.g., temperature, drought index) and no exposure to a TC. Because of the frequency of TCs during this timeframe, control periods were one to three years after the impact period. Second, we chose both a pre- and post-hurricane season control period for each TC impact within the same calendar year, with appropriate ‘wash-out' periods in between to limit carryover effects from previous systems. Associations between TCs and daily counts of mental health ED visits were examined using conditional Poisson regression models. Relative risks (RR) and p-values are reported.

Results: Using climatologically-matched control periods, TC impacts seemed protective against mental health ED visits, as visits for various conditions were lower during impact periods compared to control periods. For example, visits for depression were 6% lower (RR: 0.94; p = 0.0035) and visits for neuroses were 11% lower (RR: 0.89; p < 0.0001). These findings may be attributable to the limited health service infrastructure available post-impact in some areas. However, closer inspection of the data revealed an average 9% increase in ED visits related to mental health over the study period. The decrease in ED visits observed post-storm may have been an artifact of this overall increasing trend in ED utilization, as all control periods were in more recent years compared to their matched impact periods.

Therefore, we considered our pre-/post-hurricane control periods to eliminate the potentially confounding effect of the general increase in ED utilization on the associations of interest. Using these control periods, TC impacts were associated with an increase of 9-15% in the number of ED visits for most mental health conditions, indicating confounding was present in analyses using the climatologically-matched control periods. Specifically, visits for all mental health conditions increased by 9% (RR: 1.09; p = 0.0204), substance-related conditions increased by 11% (RR: 1.11; p = 0.0009), and organic psychotic conditions increased by 15% (RR: 1.15; p < 0.0001).

Conclusions: Examining the impacts of extreme weather events at the state-level using readily available statewide databases presents several challenges. First, we are missing individuals who are receiving mental health services outside of an ED setting, whether at temporary clinics or outside of health care settings (e.g., church or community organizations). However, ED visit data currently represents the best available statewide data source to examine such associations. We also recognize that the effects of such extreme weather events on mental health may be long-term and outside of our impact period of interest. However, evidence suggests that most individuals with initial symptoms of stress or trauma associated with natural disasters tend to return to normal functioning over time. Additional work is on-going to further improve the methods used to investigate the relationships between TCs and health outcomes.

In general, our results suggest that ED visits for mental health symptoms do increase in the immediate aftermath of a storm. EDs may be the best source of health care available immediately after impact, barring structural damage, as available resources are often targeted towards emergency services. Therefore, it is imperative that post-disaster recovery plans have programs available to deal with the mental health conditions and symptoms that may arise immediately after natural disasters.