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Susceptibility to Mortality in Weather Extremes: Effect Modification by Personal and Small-Area Characteristics

Zanobetti, Antonella; O’Neill, Marie S.; Gronlund, Carina J.; Schwartz, Joel D.

doi: 10.1097/01.ede.0000434432.06765.91

Background: Extremes of temperature have been associated with short-term increases in daily mortality. We identified subpopulations with increased susceptibility to dying during temperature extremes, based on personal demographics, small-area characteristics, and preexisting medical conditions.

Methods: We examined Medicare participants in 135 US cities and identified preexisting conditions based on hospitalization records before their deaths, from 1985 to 2006. Personal characteristics were obtained from the Medicare records, and area characteristics were assigned based on zip code of residence. We conducted a case-only analysis of over 11 million deaths and evaluated modification of the risk of dying associated with extremely hot days and extremely cold days, continuous temperatures, and water vapor pressure. Modifiers included preexisting conditions, personal characteristics, zip code–level population characteristics, and land cover characteristics. For each effect modifier, a city-specific logistic regression model was fitted and then an overall national estimate was calculated using meta-analysis.

Results: People with certain preexisting conditions were more susceptible to extreme heat, with an additional 6% (95% confidence interval = 4%–8%) increase in the risk of dying on an extremely hot day in subjects with previous admission for atrial fibrillation, an additional 8% (4%–12%) in subjects with Alzheimer disease, and an additional 6% (3%–9%) in subjects with dementia. Zip code level and personal characteristics were also associated with increased susceptibility to temperature.

Conclusions: We identified several subgroups of the population who are particularly susceptible to temperature extremes, including persons with atrial fibrillation.

Supplemental Digital Content is available in the text.

From the aDepartment of Environmental Health, Harvard School of Public Health, Boston, MA; bDepartment of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI; and cDepartment of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI.

This study was funded in part by NIEHS R21ES020695-01, NIEHS R21ES020156, and NIA T32AG027708.

This study was made possible in part by USEPA grant RD 83479801, R83275201, RD-83241601, and EPA R83275201 awarded by the US Environmental Protection Agency. Its contents are solely the responsibility of the grantee and do not necessarily represent the official views of the USEPA. Furthermore, USEPA does not endorse the purchase of any commercial products or services mentioned in the publication.

Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article ( This content is not peer-reviewed or copy-edited; it is the sole responsibility of the author.

Correspondence: Antonella Zanobetti, Department of Environmental Health, Exposure Epidemiology and Risk Program, Harvard School of Public Health, 401 Park Drive, Landmark Center, Suite 415, P.O. Box 15698, Boston, MA 02215. E-mail:

Received July 19, 2012

Accepted June 4, 2013

Copyright © 2013 Wolters Kluwer Health, Inc. All rights reserved.