A Spatial and Temporal Investigation of Medical Surge in Dallas-Fort Worth During Hurricane Harvey, Texas 2017

Abstract

Objective: When 2017 Hurricane Harvey struck the coastline of Texas on August 25, 2017, it resulted in 88 fatalities and more than US $125 billion in damage to infrastructure. The floods associated with the storm created a toxic mix of chemicals, sewage and other biohazards, and over 6 million cubic meters of garbage in Houston alone. The level of biohazard exposure and injuries from trauma among persons residing in affected areas was widespread and likely contributed to increases in emergency department (ED) visits in Houston and cities receiving hurricane evacuees. We investigated medical surge resulting from these evacuations in Dallas-Fort Worth (DFW) metroplex EDs.

Methods: We used data sourced from the North Texas Syndromic Surveillance Region 2/3 in ESSENCE to investigate ED visit surge following the storm in DFW hospitals because this area received evacuees from the 60 counties with disaster declarations due to the storm. We used the interrupted time series (ITS) analysis to estimate the magnitude and duration of the ED surge. ITS was applied to all ED visits in DFW and visits made by patients residing in any of the 60 counties with disaster declarations due to the storm. The DFW metropolitan statistical area included 55 hospitals. Time series analyses examined data from March 1, 2017-January 6, 2018 with focus on the storm impact period, August 14-September 15, 2017. Data from before, during, and after the storm were visualized spatially and temporally to characterize magnitude, duration, and spatial variation of medical surge attributable to Hurricane Harvey.

Results: During the study period overall, ED visits in the DFW area rose immediately by about 11% (95% CI: 9%, 13%), amounting to ~16 500 excess total visits before returning to the baseline on September 21, 2017. Visits by patients identified as residing in disaster declaration counties to DFW hospitals rose immediately by 127% (95% CI: 125%, 129%), amounting to 654 excess visits by September 29, 2017, when visits returned to the baseline. A spatial analysis revealed that evacuated patients were strongly clustered (Moran's I = 0.35, P < 0.0001) among 5 of the counties with disaster declarations in the 11-day window during the storm surge.

Conclusions: The observed increase in ED visits in DFW due to Hurricane Harvey and ensuing evacuation was significant. Anticipating medical surge following large-scale hurricanes is critical for community preparedness planning. Coordinated planning across stakeholders is necessary to safeguard the population and for a skillful response to medical surge needs. Plans that address hurricane response, in particular, should have contingencies for support beyond the expected disaster areas.

Keywords: hurricane; interrupted time series analysis; medical surge; spatial analysis.

FIGURE 1. Texas County-Level Disaster Declarations (n = 60) Due to Hurricane Harvey, 2017

Note: Reprinted from FEMA website: https://gis.fema.gov/maps/dec_4332.pdf. Accessed January 2019.

FIGURE 2. Predicted Visits from Interrupted Time Series (ITS) Models of Daily Emergency Department Visits compared to counterfactual trend, Metropolitan Dallas–Fort Worth, TX, March 1 2017–January 6, 2018

Note predicted visits are those predicted by the ITS model. Predicted trend is structural tred predicted by ITS model. Counterfactual trend assumes that no event occurs to interrupt the time series. Reference line “Hurricane Harvey” is August 25, 2017, the date that Hurricane Harvey made landfall in Texas. Evacuee visits are visits by patients that reported zip codes indicating residence in any of the 60 counties with emergency declarations due to Hurricane Harvey. 95% confidence band represents the confidence interval around the predicted structural trend.

FIGURE 3. Spatial Analysis of Surge in Evacuees Presenting for Care at Emergency Departments in the Dallas-Fort Worth Area Before (August 14–24, 2017), During (August 25–September 4, 2017), and After (September 5–15, 2017) Hurricane Harvey.

The zip codes in declared counties are represented with a yellow-to-dark-orange scale, representing the number of emergency department visits in Dallas-Fort Worth hospitals from people with residential zip codes in emergency-declared counties. The green-to-blue graduated circles represent the number of emergency department visits in Dallas-Fort Worth hospitals from people who reside in Texas counties with disaster declarations.