OJPHI: Vol. 5
Journal Information
Journal ID (publisher-id): OJPHI
ISSN: 1947-2579
Publisher: University of Illinois at Chicago Library
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©2013 the author(s)
open-access: This is an Open Access article. Authors own copyright of their articles appearing in the Online Journal of Public Health Informatics. Readers may copy articles without permission of the copyright owner(s), as long as the author and OJPHI are acknowledged in the copy and the copy is used for educational, not-for-profit purposes.
Electronic publication date: Day: 4 Month: 4 Year: 2013
collection publication date: Year: 2013
Volume: 5E-location ID: e156
Publisher Id: ojphi-05-156

Surveillance of Heat-related Morbidity: Relation to Heat-related Excess Mortality
Robert Mathes*1
Kristina B. Metzger2
Kazuhiko Ito1
Thomas Matte1
1New York City Department of Health and Mental Hygiene, Queens, NY, USA;
2City of Austin/Travis County Health and Human Services Department, Austin, TX, USA
*Robert Mathes, E-mail: rmathes@health.nyc.gov


To describe the extent to which heat-illness indicators increase with extreme heat and to evaluate the association among daily weather, heat-related illness and natural cause mortality.


The impact of heat on mortality is well documented [13] but deaths tend to lag extreme heat and mortality data is generally not available for timely surveillance during heat waves. Recently, systems for near-real time surveillance of heat illness have been reported [4] but have not been validated as predictors of heat related mortality. In this study, we examined the associations among weather, indicators of heat-related ambulance calls and emergency department visits and excess natural cause mortality in New York City (NYC).


We analyzed daily weather conditions, emergency medical system (EMS) calls flagged as heat-related by EMS dispatchers, emergency department (ED) visits classified as heat-related based on chief complaint text, and natural cause deaths. EMS and ED data were obtained from data reported daily to the city health department for syndromic surveillance. We fit generalized linear models to assess the relationships of daily counts of heat related EMS and ED visits to natural cause deaths after adjustment for weather conditions during the months of May–September between 1999 and 2008.


We observed an increase in mean total calls to EMS and a decrease in mean total visits to EDs during 10 observed heat waves (maximum heat index ≥90° F (Fahrenheit) for four or more consecutive days with the first three days ≥95° F and at least one day ≥100°F) in NYC between 1999 and 2008. Both EMS and EDs experienced an increase in heat-related incidents during heat waves though the increase in heat-related EMS calls was much greater. A modest increase in mean natural cause deaths was also observed. Controlling for temporal trends, an 11% (95% confidence interval (CI): 5–18) and 7% (95% CI: 4–9) increase in natural cause mortality was associated with an increase from the 50th percentile to 99th percentile of same-day and one-day lagged heat-related EMS calls and ED visits, respectively. After controlling for both temporal trends and weather, we observed a 10% (95% CI: 4–16) increase in natural cause mortality associated with one-day lagged heat-related EMS calls and a 5% mortality increase with one-day lagged ED visits (95% CI: 2–8).


Heat-related EMS calls and ED visits lagged one day predicted natural cause mortality in our temporal and weather-adjusted model. In particular, risk of mortality rapidly increased as the number of heat-related EMS calls approached high levels (>100 heat-related calls/day). Heat-related illness can be tracked during heat waves using EMS and ED data which are indicators of heat associated excess natural cause mortality during the warm weather season.


This research was funded by the Environmental Protection Agency, STAR Grant R833623010, and in conjunction with the Alfred P. Sloan Foundation, grant 2010-12-14. We thank the members of the New York City Department of Health and Mental Hygiene Syndromic Surveillance Unit.

1.. Curriero FC, et al. Temperature and mortality in 11 cities of the eastern United StatesAm J Epidemiol 2002;155(1):80–7.
2.. Dolney TJ, Sheridan SC. The relationship between extreme heat and ambulance response calls for the city of Toronto, Ontario, CanadaEnviron Res 2006;101(1):94–103.
3.. Knowlton K, et al. The 2006 California heat wave: impacts on hospitalizations and emergency department visitsEnviron Health Perspect 2009;117(1):61–7.
4.. Chau PH, Chan KC, Woo J. Hot weather warning might help to reduce elderly mortality in Hong KongInt J Biometeorol 2009;53(5):461–8.

Article Categories:
  • ISDS 2012 Conference Abstracts

Keywords: Surveillance, Heat, Morbidity, Mortality.

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org