Dive Brief:

• Rates of Legionnaires' disease are higher in ZIP codes served by water treatment plants that use chlorine rather than monochloramine as the primary disinfectant, according to preliminary results from a nationwide epidemiological study.
• Rates are also higher when the plants use chlorine as the secondary disinfectant, according to the study, which the authors will release tomorrow, Dec. 10, at a Society for Risk Analysis meeting in Washington, D.C.
• “It is important to think about the whole life of the water, from treatment to tap, when we consider how to best manage this pathogen and lower the incidence of Legionnaires’ disease,” Alexis Mraz, author of the study and an assistant professor of public health at The College of New Jersey, said in a statement.

Dive Insight:

Legionnaires’ disease has been in the news since July, when several people died and dozens were sickened in New York City by the bacteria that causes the disease.  

The outbreak was likely caused by a cluster of commercial property cooling towers, New York City health officials said, after they found high concentrations of the bacteria in the vapor coming from the cooling towers.

Although there are steps facilities managers can take to control the growth of the bacteria in their water systems, their job is made easier if the water treatment plant that serves their area controls the bacteria before it gets to their facility, the findings suggest. 

“Once it establishes a niche … Legionella is extremely challenging to treat and manage in a building’s plumbing system,” Mraz said.  

For their study, researchers looked at historical data from 25 water treatment plants spread over the 10 U.S. Environmental Protection Agency regions.  

The analysis found that rates of Legionnaires’ disease among residents served by the utilities ranged from no reported cases to an average of 8.36 cases per 100,000 people. The higher rates are associated with the use of chlorine as the primary disinfectant or with the use of chlorine as the secondary disinfectant, according to the summary. Monochloramine is a form of chlorine that contains ammonia, according to the U.S. Centers for Disease Control information sheet.

Seasonality was also a factor, with higher rates occurring more frequently in summer months. 

The findings track other study findings, including some focusing on healthcare facilities, that found a lower prevalence of Legionnaires’ disease in facilities that use monochloramine as their primary water treatment.

“Monochloramine nearly eliminated [the Legionella pneumophila bacteria],” one study, published last fall in the journal Water Research, found. 

Municipalities are gradually switching from chlorine to monochloramine, according to Los Angeles-based water treatment company Culligan. “Chlorine remains common but chloramine is seeing increasing adoption, especially in densely populated areas,” the company says.

Chlorine became the water treatment of choice after World War II, in part because of ammonia shortages, according to a publication called “New England Water Supplies – A Brief History.”