Bold claim: A strategic overhaul of how we treat water could dramatically reduce deadly disease outbreaks. But here’s where it gets controversial: the scale of impact may hinge on local infrastructure and unseen water quality factors. A new study from the University of Minnesota Twin Cities provides fresh evidence that targeted changes to disinfection practices can stop a Legionnaires’ disease outbreak by treating groundwater that had previously gone untreated.
In this report, published in Emerging Infectious Diseases, researchers show for the first time that introducing disinfection to groundwater, which had not previously received such treatment, helped halt an outbreak. Legionnaires’ disease is a serious form of pneumonia caused by the bacterium Legionella pneumophila. It thrives in water systems such as cooling towers and water heaters and remains the leading waterborne illness in many developed nations.
During 2023 and 2024, Grand Rapids, Minnesota, documented 34 confirmed cases and two deaths. An in-depth look at the city’s water and building infrastructure uncovered troubling levels of Legionella across the community’s facilities.
“This study is one of the first to directly link a Legionnaires’ disease outbreak to an entire community water system,” said Molly Bledsoe, a University of Minnesota environmental engineering alumnus and the paper’s lead author.
To curb transmission, Grand Rapids adopted chloramine disinfection. Since this change, Legionella levels have fallen below detectable limits, and the city has reported no new Legionnaires’ disease cases.
“Our findings reveal a critical gap in public health safety,” emphasized Tim LaPara, professor of Civil, Environmental, and Geo- Engineering at the University of Minnesota and one of the study’s senior authors. He noted that many smaller or rural towns depend on untreated groundwater, often assuming it to be naturally shielded. Elevated levels of assimilable organic carbon (AOC)—a bacterial nutrient present in some groundwater—may have fueled the outbreak in Grand Rapids.
AOC is a water quality parameter that is not routinely measured, particularly in smaller communities and rural areas. The research team hopes to extend this work to examine whether other groundwater-supplied community systems also exhibit high AOC levels and could benefit from proactive disinfection measures.
In addition to Bledsoe and LaPara, the Minnesota team comprised graduate student Maya Adelgren, post-doctoral researcher Apoorva Goel, and project co-leader Raymond Hozalski.
The study was supported by the United States Environmental Protection Agency.
For those seeking the full details, the paper is titled “Effect of Chloramine Disinfection of Community Water System on Legionnaires’ Disease Outbreak, Minnesota, USA, 2024,” and is available on the U.S. Centers for Disease Control and Prevention website (https://wwwnc.cdc.gov/eid/article/32/1/25-1232_article#).
Would you consider expanding groundwater monitoring to routinely include AOC measurements in your area, and what might be the practical hurdles to implementing chloramine disinfection in smaller towns? Share your thoughts in the comments.
