The biggest electricity blackout to occur in the United States resulted in 90 additional deaths in New York City, caused both by accidents and disease-related problems, according to a new analysis of data from the summer of 2003.
"Our results from this study indicate that power outages can immediately and severely harm human health," said Brooke Anderson, the lead author of the study and a researcher at Johns Hopkins University.
Anderson said her study is the first to show that the death toll of an outage comes not only from more accidents -- like carbon monoxide poisoning from generators -- but also from cardiovascular, respiratory and other chronic health conditions.
Little is known about the health impact of power outages, Anderson and a colleague write in the journal Epidemiology. They note that estimates of mortality in natural disasters, like hurricanes, typically include only directly attributable deaths, such as from drowning, even though power is usually lost in the disaster as well.
To get a sense of the mortality stemming from a power outage itself, they collected data on New York City's weather conditions, air pollution levels and causes of deaths reported during the blackout in August of 2003.
Though most of New York City was dark for only about a day, August 14 to 15, the blackout affected a wide swath of the northeastern United States and Canada, lasting as long as four days in some places, including pockets within the city.
Afterwards, the New York City health department attributed only six deaths to the blackout, most of them from carbon monoxide poisoning.
Anderson, however, found there was an overall 28 percent spike in deaths during the city's power outage.
Twelve of those additional deaths were caused by accidents, 38 by cardiovascular conditions, three from respiratory problems and 37 by various other health conditions.
Conditions during the blackout might explain why health problems can worsen during a power outage.
For instance, "people were trapped in the subway in the dark and didn't know what happened. Especially after September 11, people are more scared, and stress can trigger a heart attack or exacerbate asthma," said Shao Lin, an epidemiologist with the New York State Department of Health, who was not involved in this study.
Firefighters also had to rescue hundreds of people from elevators and many residents in high-rise apartments had no running water for the duration.
In an email to Reuters Health, Anderson pointed out that people also could have had difficulty managing their diseases.
"For example, most food sources and pharmacies were closed, which could be a serious problem for someone with diabetes or someone who is low on prescription medicines," she said.
Ambulances were slower, home medical equipment that used electricity couldn't operate and cell phones didn't work during part of the blackout.
The weather was very warm, but did not qualify as a "heat wave" during the disruption.
Pollution monitors weren't working through the outage, but shortly afterward there was an uptick in certain air pollutants, the researchers found.
Lin told Reuters Health that increased air pollution from idling buses or other sources could also aggravate respiratory conditions and lead to increased deaths.
In a previous study, she and her colleagues found that hospital admissions for respiratory conditions increased during the blackout.
Anderson said that because of increased stress on power grids, blackouts could become more common in the future.
Lin said she and others are continuing to study the effects of power outages to help emergency responders better address the needs of communities and target help to the people at the most risk.
Energy companies are also working to stop power outages from happening in the first place, such as during heat waves when power grids struggle, Anderson said.
"The most direct way to reduce excess deaths from a blackout is to try to prevent blackouts," she said.