A vast electricity blackout in the United States and Canada in 2003 led to the deaths of nearly 100 people, a study found, linking the deaths -- higher than official estimates -- to not only accidents caused by lack of power, but also underlying diseases.
Researchers said the study published in the journal Epidemiology was the first to show that the death toll of such a power outage comes not only from accidents, such as carbon monoxide poisoning from using generators, but also from chronic health issues such as cardiovascular and respiratory problems.
"Our results from this study indicate that power outages can immediately and severely harm human health," said lead author Brooke Anderson, a researcher at Johns Hopkins University.
Little is known about the health impact of power outages, Anderson and a colleague wrote.
To get a sense of the mortality from a blackout, they collected data on New York City's weather conditions, air pollution levels and causes of deaths reported during the blackout in August 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 cases -- including some 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.
But Anderson found there was an overall 28 percent spike in deaths during the 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 a blackout may explain why health problems can worsen. Many residents in high-rise apartments had no water for the duration, for example, and firefighters had to rescue hundreds of people from elevators.
"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 the study.
Increased air pollution from idling buses or other sources could also aggravate respiratory conditions, Lin said. In a previous study, she and her colleagues found that hospital admissions for respiratory conditions increased during the blackout.
Though pollution monitors didn't work through the outage, shortly afterward there was an uptick in certain air pollutants, the researchers said.
Anderson said that people with chronic health issues could also have problems managing them.
"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 in an email.
Ambulances were slower, home medical equipment that used electricity couldn't operate and cell phones didn't work during part of the blackout.
Anderson said that while energy companies are working to stop power outages from taking place in the future, such as during heat waves when power grids struggle, increased stress on the grids could make blackouts more common in the future.
"The most direct way to reduce excess deaths from a blackout is to try to prevent blackouts," she said.
(Reporting from New York by Kerry Grens at Reuters Health; editing by Elaine Lies)