Researchers say there's a definite link between the 2014-15 outbreak of Legionnaires' disease cases in Michigan following the switch in Flint's drinking water supply to the Flint River.

Although the outbreak of Legionnaires' happened at the same time as the Flint water crisis, it was initially unclear how the two were connected.

The Flint Area Community Health and Environment Partnership pinpointed the blame on low chlorine levels in Flint's water system during the water crisis that lead to the deadly outbreak that killed 12 people and sickened at least 87.

“Our study shows that during the water crisis, the risk of a Flint resident having Legionnaires’ disease increased as the amount of free chlorine in their water decreased,” said Shawn McElmurry, associate professor of civil and environmental engineering at Wayne State University and the FACHEP principal investigator. “Since municipalities typically evaluate the risk of waterborne illnesses by measuring free chlorine, a better understanding of how chlorine is deactivated can inform future water management policies and practices.”

The researchers conducted an exhaustive analysis of data on Legionnaires’ cases in Genesee, Wayne and Oakland Counties from 2011 to 2016. FACHEP researchers determined that in 2014-15 there was an increase in the risk of acquiring Legionnaires’ disease across the Flint water distribution system that is consistent with a system-wide proliferation of Legionella bacteria. An estimated 80 percent of Legionnaires’ cases during this period are attributable to the change in water supply, according to the research. 

Researchers found when the water was supplied from the Flint River, Flint residents were seven times more likely to develop Legionnaires' disease.

You can read the full report here.