Study Finds Low Chlorine Led to Flint, Mich., Legionnaires' Outbreak

Scientists found the lead reacted with the chlorine to create an environment more hospitable to legionella bacteria

Study links low chlorine to legionnaires'

New research published in the Proceedings of the National Academy of Sciences by a team of scientists from the University of Michigan, Colorado State University and Wayne State University revealed low chlorine levels as the cause of the 2014 to 2015 Legionnaires’ disease outbreak in Flint, Mich. The scientists analyzed water and epidemiological data from the six year period before, during and after the Flint water crisis.

Chlorine reacts with heavy metals, such as lead, and the study suggested that the lead in the water distribution system may have decreased the amount of chlorine through that reaction. While the same amount of chlorine was used in the system as before the switch to the Flint River, the reaction caused the chlorine to be less effective in combating legionella bacteria.

In a normal year the disease would occur between six and 12 times in Flint, however, during the crisis Legionnaires’ disease occurred in approximately 45 cases per year, as reported by National Public Radio (NPR).

“The really striking finding from our research is that the amount of chlorine that needs to be present is actually influenced by other factors in this large municipal water system,” Michele Swanson, a Legionnaires’ expert from University of Michigan involved in the study told NPR. “So, for example, during the Flint water crisis, the amount of chlorine that needed to be present to reduce the risk of disease was much higher than normal.”

The study’s authors are optimistic that the findings will inform policy decisions in regard to the frequency of testing for legionella bacteria.


the switching of water supplies

So the switch of water supplies was still the cause of the legionella bacteria and the existing lead in the supply system was reducing the effectiveness of the chlorine?

Or was the supply system itself the breeding ground of the bacteria and the switching of supply water had nothing to do with the cause?

My understanding is that the

My understanding is that the lead that resulted from corrosion reduced the effectiveness of the chlorine. Even though the city was adding higher concentrations of chlorine, the reaction with the lead and iron corrosion altered the effectiveness of the chlorine ultimately making an ideal breeding ground for legionella bacteria. Hope this answers your question. Here is the actual study if you'd like to explore in more depth:
-WQP Editor

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