With climate change, extreme heat (EH) events are increasing, so it is important to understand who is vulnerable to heat-associated morbidity. We determined the association between EH and hospitalizations for all natural causes; cardiovascular, respiratory, and renal diseases; diabetes mellitus; and acute myocardial infarction in Michigan, USA, at different intensities and durations. We assessed confounding by ozone and how individual characteristics and health insurance payer (a proxy for income) modified these associations. We obtained Michigan Inpatient Database, National Climatic Data Center, and US Environmental Protection Agency ozone data for May–September, 2000–2009 for three Michigan counties. We employed a case-crossover design and modeled EH as an indicator for temperature above the 95th, 97th, or 99th percentile thresholds for 1, 2, 3, or 4 days. We examined effect modification by patient age, race, sex, and health insurance payer and pooled the county results. Among non-whites, the pooled odds ratio for hospitalization on EH (97th percentile threshold) vs. non-EH days for renal diseases was 1.37 (95 % CI = 1.13–1.66), which increased with increasing EH intensity, but was null among whites (OR = 1.00, 95 % CI = 0.81, 1.25). We observed a null association between EH and cardiovascular hospitalization. EH (99th percentile threshold) was associated with myocardial infarction hospitalizations. Confounding by ozone was minimal. EH was associated with hospitalizations for renal disease among non-whites. This information on vulnerability to heat-associated morbidity helps characterize the public health burden of EH and target interventions including patient education.
Hospitalization Temperature Morbidity Heat wave Heat
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This research was funded by the US Centers for Disease Control and Prevention (grant EH000348), the National Institute of Environmental Health Sciences (grant R21-ES020156), the National Institute on Aging Interdisciplinary Research Training in Health and Aging (grant T32AG027708), and a University of Michigan Graham Sustainability Institute Dow Sustainability Fellowship. We would also like to thank members of the “Climate change and health: Residential energy-efficiency for comfort and equity” project for their input and guidance and the Division of Vital Records and Health Statistics of the Michigan Department of Health and Human Services for MIDB data access and support. RW and LC were associated with CDC Cooperative Agreement IUE 1EH000744 during the time this study was conducted. The contents of this study are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention.
Portions of this data are taken from a proprietary database owned and maintained by the Michigan Health and Hospital Association Service Corporation (MHASC). All rights reserved. This data may not be used for commercial purposes without first obtaining written permission from the MHASC. Contact MHASC at firstname.lastname@example.org for more information.
Compliance with ethical standards
The research was determined exempt by the University of Michigan Health Sciences and Behavioral Sciences Institutional Review Board.
Conflict of interest
The authors declare that they have no conflict of interest.
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