The number of Connecticut cases of Legionnaires’ disease has increased in recent years, and a new Yale University study indicates that people living near the Quinebaug and Naugatuck river watersheds have the highest risk of catching the illness.
Still, only about 5 percent of people who are exposed to the bacteria that causes Legionnaires’ disease actually contract the illness, according to experts. An average of 51 people a year are hospitalized with Legionnaires’ in Connecticut and state records show the fatality rate is about 10 percent.
Yale School of Public Health researchers who conducted the study and state health officials say there is no indication that people can get this fairly rare respiratory disease through direct contact with those bodies of water.
Kelsie Cassell, the lead author of the study, said Tuesday there is still no concrete answer to the question of why residents living around these rivers should have a higher incidence of Legionnaires’ disease than people in other parts of the state. The research indicated that people living within 10 miles of the Quinebaug River had the “highest increased risk of [Legionnaires’] disease.”
The findings of the year-long study, which has now been published in The Journal of Infectious Diseases, came as a surprise to Cassell and other researchers. “You would expect to find higher numbers [of Legionnaires’ disease] in the cities” rather than along certain watershed areas, said Cassell, a 24-year-old post-graduate research assistant at the school.
But there are some potential suspects in this medical detective story. Two possibilities are power plants that use water from those rivers in their cooling systems, or sewage treatment plants in the region, according to the study.
Both types of facilities use processes that can “aerosolize” the river water, converting the liquid into a fine spray that could allow any Legionella bacteria present to be inhaled by people in the area.
The new Connecticut study also confirmed previous research showing that weather can play a role in the spread of this disease, with more cases showing up after periods of increase rainfall and humidity. That finding is also worrisome, given predictions by many climate scientists that global warming is likely to trigger more rainfall and bigger storms.
Cassell said the Legionella bacteria that causes the illness is often present in natural water systems. “We’re not trying to say don’t go swimming in your healthy rivers or lakes,” she said. “We’re not saying you can contract this disease from these particular water bodies.”
“It only becomes a [public health] issue further downstream in public or private water systems,” she said. Most people associate the disease with issues involving water cooling towers or public drinking supplies in places like hotels, Cassell added.
The elderly and those with compromised immune systems or chronic lung problems are at the greatest risk from Legionnaires’ disease, and research indicates they are at higher risk of infection during warmer summer months.
“It’s not a high risk for most people,” Cassell said.
The disease was named as a result of a mass outbreak in Philadelphia in 1976 during an American Legion convention, and involved bacteria in a hotel water cooling tower. There was a more recent outbreak in Flint, Mich., that was related to the public water crisis in that city.
Between 8,000 and 18,000 cases of disease caused by the Legionella bacteria result in hospitalization in the U.S. annually, according to state officials. The last outbreak in Connecticut happened in 1995 and involved patients at a hospital contracting the disease.
Matthew Cartter, Connecticut’s state epidemiologist, said in an email the concern in this state is that the rate of sporadic, individual cases of Legionnaires’ disease has been increasing. An earlier study found that, between 2003 and 2012, the incidence of this illness in Connecticut increased from 0.78 cases per 100,000 population to 1.57 cases per 100,000 people.
In 2016, Cartter asked Yale School of Public Health scientists to investigate the rise in Legionnaires’ cases, which he said had “confounded investigators.” Daniel Weinberger, an assistant professor of epidemiology at the school, and Cassell, Weinberger’s research assistant, “accepted the Legionnaires’ disease challenge,” Cartter said.
State Department of Public Health officials are now working with Cassell and other Yale researchers to try and pin down exactly how the Legionella bacteria is infecting people in those higher-risk watershed areas in both eastern and western Connecticut.
“We’ve started sampling of rivers to see if the bacteria are present,” Cassell said.
Cassell said she is also contacting health officials in Massachusetts to see if they’ve had similar clusters of Legionnaires’ cases around certain river or watershed systems in that state.
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