Asthma-related hospitalizations increase significantly during the summer when there are more rainstorms and severe heat, according to new research from the University of Maryland School of Public Health.
The researchers expect climate change to amplify these weather patterns, compounding problems for asthma sufferers and straining public health as the planet warms.
"People don't realize that climate change is having an impact here," said Amir Sapkota, the study's senior author and an associate professor at the Maryland Institute for Applied Environmental Health. "It's not only people in Bangladesh, it's not just the polar bear. This is how people in Maryland are experiencing it."
The researchers obtained a database of 12 years' worth of Maryland hospitalization records and looked for links between severe weather and hospitalizations. They found that an extremely hot day in the summer was linked to a 23 percent higher risk of hospitalization for asthma while an extremely rainy day was linked to an 11 percent higher risk.
With rising temperatures and extreme weather becoming more common, the impact on public health could be significant, the researchers said.
Using the researchers' data, the state Department of Health and Mental Hygiene projects that hospitalization rates for asthma in Baltimore will more than double by 2040.
An estimated 359,000 Marylanders, or 8.4 percent of the population, had asthma in 2010, according to the health department. Young people were more likely to have asthma, which also has links to race and poverty. Up to 20 percent of children in Baltimore City have asthma, compared with the national average of 9.4 percent, according to government data.
The U.S. Centers for Disease Control and Prevention estimates that asthma costs the nation $56 billion annually in health care costs, lost work days and premature deaths. The average yearly cost of care for a child with asthma was $1,039 in 2009, according to the CDC. It also leads to an estimated 10.5 million missed days of school and 14.2 million missed days of work annually.
Sapkota and his team also found links between extreme heat and rain events and a heightened risk of hospitalization from other causes, including car crashes, heart attacks and foodborne illnesses such as salmonella.
They analyzed a database of 115,923 hospitalizations in Maryland from 2000 to 2012.
The reasons for these links aren't always clear, Sapkota said. Very hot days often lead to a rise in the amount of ozone in the atmosphere, which is a known trigger for asthmatics. But scientists are less sure how heavy rain could contribute to asthma attacks — it could be because rain causes pollen spores to open.
"It's still up for debate," Sapkota said.
Children ages 5 to 17 were more likely to be hospitalized for asthma during extreme heat, while asthmatic children under 5 were more likely to be hospitalized during extreme rain, the researchers found.
Sapkota's team analyzed hospitalizations on the day of, the day before, and two days before an extremely hot day or a downpour. They considered a weather event severe if the rainfall or heat was in the 90th and 95th percentile of heat or rain, based on 30-year averages.
The results were published in the April issue of the journal Environmental Health and also were used in the April report on climate and health by the state health department, which projected the future increase in asthma hospitalizations.
The health department also projected there will not be a significant rise in extreme rain through 2040, but it does expect the number of severely hot days to rise.
Clifford S. Mitchell, director of the environmental health bureau at the state health department, said people are generally aware that climate change could affect their health.
"People are very concerned about the effects of climate change on them and their children and grandchildren," he said. "It's one of the most significant concerns people have about climate change."
Mitchell said the team chose 2040 as its projection point to "give people a sense that this is not something way, way, way far in the future. It's something their children and grandchildren will experience."
Kathryn S. Robinett, an assistant professor of medicine at the University of Maryland School of Medicine, said rates of asthma hospitalization are usually lowest in the summer. In other months, allergies and infections picked up in school, as well as winter colds, can contribute.
The most common reason an asthmatic needs to be hospitalized is poor compliance with medication — just 30 percent of asthmatics use their medication properly all the time, she said.
Climate change could allow the rate of summer asthma hospitalizations to "catch up" to other seasons, Robinett said.
She recommends asthmatic patients be consistently compliant with controller medications, "but to be especially compliant during extreme weather so you don't end up in the hospital. The best way to prevent hospitalizations, no matter what the trigger is, is to be good about taking your controller medication during those times."
Mitchell said public health officials hope to use the data to spark a conversation about how to address the likely rising rates of asthma hospitalizations and other issues in the future.
"We don't know how big those [climate] changes are going to be," Mitchell said. "The important thing is for us not to pretend that they're not happening, but to talk about the change, the projections on health and talk about how our public health systems are adequately prepared for those changes."