As reported cases of Legionnaires’ disease climb in the United States — there have been three major outbreaks in the news this summer — researchers say the increase could be partly a result of climate change.
More than three times as many cases of legionellosis, of which Legionnaires’ disease is one form, were reported in 2009 than 2000 — 3,522 up from 1,110, according to a report from the Centers for Disease Control and Prevention.
This year the disease has broken out at a western Illinois veterans home, at San Quentin State Prison near San Francisco and in New York City, which has seen a similar rise in the disease. Its incidence of cases increased 230 percent from 2002 to 2009, with the greatest number in high-poverty neighborhoods, according to an October study in the CDC journal Emerging Infectious Diseases.
Legionnaires’ disease, identified after 34 deaths among American Legionnaires returning from a 1976 convention in Philadelphia, is a sometimes deadly pneumonia that is spread through the environment, rather than person to person, often in a mist of contaminated water from cooling towers, hot tubs, showers or faucets. It is not contagious.
Dr. David N. Fisman, a professor at the Dalla Lana School of Public Health at the University of Toronto, said in an email that he doubted the increase was the result solely of improved testing. The rise is linear and across all regions of the United States, he said.
It is difficult to be certain that climate change is a factor but it seems plausible, he said. The bacteria is more infectious in warm temperatures and some studies, including one he and others did in 2005, have shown that wet, humid weather predicts an upsurge in the risk of contracting the disease over the following week or two. That finding was not replicated in Toronto, he said, but there the disease peaks later in October in that area.
“Given that we know climate change is going to make for hotter, stormier summers (and already is doing so) it doesn’t seem like a huge leap to suggest that the ongoing rise in legionellosis in the US could be at least partly due to climate change,” he wrote.
Why humidity would increase the risk of legionellosis is not known. Increased air conditioning use, with the bacteria potentially in the dripping water, could be a factor, or it might be that the true culprit is summertime rainfall, he said.
The outbreak at the veterans home in Quincy, Illinois, has left seven dead so far. Officials with the Illinois Department of Veterans Affairs and the state Department of Public Health said that each of the victims had underlying medical conditions. Their average age was 86.
Thirty-nine residents have been sickened, and test results for others remain pending.
At San Quentin State Prison near San Francisco, six cases had been confirmed among inmates by the end of August. Another 85 inmates were under observation. To stem additional infections, officials initially put the prison on lockdown and shut down its plumbing.
In the Bronx, 12 people were killed and 100 became ill in July and August before the disease was controlled. The source was found to be a cooling tower on the roof of a historic hotel. New York now requires towers to be cleaned, inspected and registered.
A commentary in the Bulletin of the World Health Organization on March 27 argued for adding it to the Intergovernmental Panel on Climate Change's list of important climate-sensitive health issues.
The CDC’s Morbidity and Mortality Weekly Report of Aug. 19, 2011, from Dr. Lauri Hicks and others, noted that the incidence rates increased nearly threefold from 2000 to 2009. The totals likely underestimate the actual cases, because the tracking system depended on health-care providers and laboratories to report cases. The rise underscores the need to test adults for Legionnaires' disease and to report cases, they wrote.
The New York study, which reviewed cases through 2011, also found disparities among race and ethnicity, with the highest incidents among non-Hispanic black residents, and greater risk among certain occupations, including janitors and cleaners.
Legionnaires' disease usually appears two to 10 days after exposure to the bacteria. Symptoms include shortness of breath, high fever, chills and chest pains. People with Legionnaires' disease also experience appetite loss, confusion, fatigue and muscle aches.
Those at highest risk are the elderly, cigarette smokers, people with chronic lung or immune system disease and those receiving immunosuppressive drugs. Most cases can be treated successfully with antibiotics — which is why those who have symptoms should seek immediate medical care.
Dr. Ruth Berkelman, a professor at Emory University’s Rollins School of Public Health, reported on the increased incidence of legionellosis from 1990 until 2005, particularly in the eastern United States and more recently on the need for national public health authorities to review prevention policies.
“Legionellosis deserves a higher public health priority for research and policy development,” she and her co-authors wrote in the Journal of Public Health Management Practices in September.