Assessing community-wide health impacts of natural disasters: studies of a severe flood in Beijing and tropical cyclones in the United States
Date
2018
Authors
Yan, Meilin, author
Anderson, G. Brooke, advisor
Peel, Jennifer L., advisor
Magzamen, Sheryl, committee member
Wilson, Ander, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Death and injury tolls occurring during natural disasters have traditionally been estimated using a disaster surveillance approach, where each death or injury is considered case-by-case to determine if it can be attributed to the disaster. This approach may not always capture the overall community-wide health effects associated with disaster 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 disaster-related risks that are rarer outside of storm events (e.g., drowning, carbon monoxide poisoning, trauma). The goal of this dissertation is to examine the community-wide impacts of natural disasters on some common health outcomes. To achieve this goal, we assessed the community-wide health risks from exposure to two types of climate-related natural disasters, a severe flood and tropical cyclones, as compared with matched unexposed days in the same community. Our results can provide new evidence on how natural disasters affect human health, contributing to and complementing the large base of existing literature generated using a disaster surveillance approach. Mortality risk of a severe flood. On July 21–22, 2012, Beijing, China, suffered its heaviest rainfall in 60 years, which caused heavy flooding throughout Beijing. We conducted a matched analysis comparing mortality rates on the peak flood day and the four following days to similar unexposed days in previous years (2008–2011), controlling for potential confounders, to estimate the relative risks (RRs) of daily mortality among Beijing residents associated with this flood. Compared to the matched unexposed days, mortality rates were substantially higher during the flood period for all-cause, circulatory, and accidental mortality, with the highest risks observed on the peak flood day. No evidence of increased risk of respiratory mortality was observed in this study. We estimated a total of 79 excess deaths among Beijing residents on July 21–22, 2012; by contrast, only 34 deaths were reported among Beijing residents in a study estimating the flood's fatality toll using a traditional surveillance approach. Results were robust to study design and modeling choices. Our results indicate considerable impacts of this flood on public health, and that much of this impact may come from increased risk of non-accidental deaths. To our knowledge, this is the first study analyzing the community-wide changes in mortality rates during the 2012 flood in Beijing, and one of the first to do so for any major flood worldwide. This study offers critical evidence in assessing flood-related health impacts, as urban flooding is expected to become more frequent and severe in China. Health risk of tropical cyclones. To measure storm exposure, we separately considered five metrics—distance to storm track; cumulative rainfall; maximum sustained wind speed; flooding; and tornadoes. For mortality outcomes, we used community vital records for 78 large eastern United States (U.S.) communities, 1988–2005, to estimate the risks of storm exposure on four mortality outcomes. 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. We compared the health outcome rates across the study population (all community residents for the mortality analysis; community Medicare beneficiaries for the hospitalization analysis) 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. For the mortality analysis, 92 Atlantic Basin tropical cyclones were considered based on U.S. landfall or close approach, with 70 communities exposed to at least one storm; for the hospitalization analysis, 74 storms were considered for 175 exposed counties. Under the wind-based exposure metric, we found substantially elevated risk for all mortality outcomes considered compared with matched unexposed days, with risk typically highest on the day of the storm's closest approach. When excluding the ten most severe storm events based on wind exposures, however, we did not observe significantly increased risk for the remaining storm exposures on any mortality outcomes. Among Medicare beneficiaries, the cumulative risks of respiratory hospitalizations were increased under all storm exposure metrics considered, for all storm exposures and across all exposed counties; these risks remained significantly elevated even when the ten most severe storm exposures (based on wind exposure) were excluded. Our findings on community-wide health risks from tropical cyclones add important insights to results from disaster surveillance: first, the impacts of tropical cyclones on non-accidental mortality can, in some cases, be much greater than identified in case-by-case surveillance studies; second, there is strong evidence that risks of Medicare emergency hospital admissions due to non-injury morbidity are elevated during the storm exposure period; and third, intense wind exposure can characterize many of the tropical cyclone exposures with particularly high risk on non-accidental mortality, as well as respiratory hospitalizations in the elderly.