Heat-related mortality, public awareness and behaviors: implications for messaging and prevention

Background:

Extreme heat kills more Americans every year on average than all other natural disasters combined. Despite this fact, the nature of heat waves and their public health impacts pose challenges for communicating prevention messages through mass media and directly to the public. Heat waves are rather common (about 2 to 4 occur in a typical New York City summer) and are generally not associated with dramatic visual images such as from a coastal storm. Also, unlike other natural disasters, the full public health impacts of heat waves are typically only known for some time after the event and media coverage has ended. The complete ascertainment of deaths from hyperthermia (heat stroke) may inherently lag for days or weeks, and the larger number of excess deaths from natural causes must be estimated statistically after complete daily mortality counts are available for the summer season.

This presentation will describe recent findings on risk factors for heat stroke mortality among NYC residents and the results of a 2011 survey that characterized awareness of heat alerts and advisories, behaviors during hot weather, and risk perception.

Methods:

Part 1: Heat Wave Mortality Surveillance We conducted surveillance of hyperthermia deaths in NYC from 2008-2011 following heat waves that resulted in five or more deaths. We reviewed death certificates, autopsy reports, and death scene investigation reports to describe environmental and underlying medical risk factors for heat stroke deaths (n=50). Although heat stroke deaths account for a minority of deaths caused by heat waves (the rest being excess deaths from natural causes) they are identifiable on an individual level, unlike excess natural-cause deaths, permitting the investigation of risk factors and circumstances leading up to the fatality.

Part 2: Use of Air Conditioning, Awareness of Heat Alerts, and Risk Perception In collaboration with Baruch College, we conducted a random digit-dial telephone survey of approximately 700 New Yorkers in September 2011. We asked participants about air conditioning (A/C) ownership and use, awareness of heat alerts and advisories, and what participants did to stay cool if they did not have air conditioning at home. The surveys were followed by four focus groups in English and Spanish: two with seniors and two with potential senior-caregivers (n=38) to discuss heat awareness and risk perception in greater depth.

Results:

Part 1: Heat Wave Mortality Surveillance Heat stroke victims ranged from 10 to over 90 years of age, with the highest rates occurring among adults 65 years of age and older. Many had significant pre-existing co-morbidities such as cardiovascular disease (74%), a history of substance abuse (30%), psychiatric illness such as schizophrenia or other cognitive impairment (16%), diabetes (16%), or a breathing condition such as emphysema (8%). Obesity was common (43%) among decedents under 65 years of age (n=26) and cerebral palsy was a prevalent disability (12%).

The vast majority of victims (84%) were overcome by heat in their own homes, none of which had a fully working air conditioner, where environmental information was available (n=26). Seven reports noted that a standing fan or window fan had been in use when the individual died. Twenty-eight (66%) of the victims lived alone.

Part 2: Use of Air Conditioning, Awareness of Heat Alerts, and Risk Perception Eleven percent of survey respondents did not have any A/C, and another 14% rarely or never used their A/C during very hot weather in the past summer. This corresponds to an estimated 1.6 million New Yorkers. Many who went without A/C also had an elevated risk of heat-related mortality due to age or poor health, corresponding to roughly 500,000 New Yorkers. About half of this high-risk population reported that they stayed at home during hot weather despite being unable to stay cool.

Barriers to A/C ownership included cost (50%), the perception that A/C was not needed (26%), and a dislike of A/C (15%). A large majority (77%) of respondents heard or saw a heat warning in 2011. Among this group, 75% received warnings from TV, 9% from the radio, and 7% from the internet. About half (54%) reported checking on a family member, friend, or neighbor during very hot weather.

Among focus group members, most were not aware of the high risk associated with un-air conditioned indoor environments. After being shown recent media coverage on heat waves, the participants felt that the stories, predominated with visuals of outdoor scenes, did not convey a strong take-home message about indoor exposure risks.

Discussion:

Heat stroke deaths caused by recent heat waves in New York City share risk factors described during prior heat waves in northern U.S. cities. The high rate of co-morbidities included a disproportionate number of obese individuals, a trend that will likely continue to increase vulnerability to extreme heat in upcoming years.

Indoor environments without air conditioning, especially in dense urban areas, can be very dangerous for people at-risk. In fact, studies show that temperatures in some city apartments may be more than 10°C higher than outdoor temperatures. Still, many vulnerable New Yorkers who do not use air conditioning also do not perceive a need for it. And despite being unable to stay cool, most of those without air conditioning stay at home by necessity or by choice rather than going to an air conditioned place.

With average summertime temperatures on the rise, heat related illness and mortality will likely climb unless further adaptation takes place. An important component of most urban heat emergency response plans is advising the public to take precautions, especially if they are at risk, and to check on vulnerable friends, neighbors and family members. More than any other type of media, most New Yorkers turn to TV news and weather reports for alerts about extreme heat. Improvements in visual and verbal messaging in the mainstream media around the dangers of the indoor environment and who is most at risk during heat waves have the potential to change risk perception on a large scale.