The outbreak of Legionnaires’ disease in 2014-15 in Flint, Michigan, was likely caused by a change in the city’s drinking water supply, according to a study led by Colorado State University researchers.

Sammy Zahran, associate professor in the Department of Economics at CSU, was the lead author of an article about the study being published this week in the Proceedings of the National Academy of Science (PNAS). CSU Economics Professor David Mushinski was a co-author.

Based on a detailed statistical analysis of multiple datasets by Zahran and his co-authors, the Flint Area Community Health and Environment Partnership (FACHEP) found that the majority of Legionnaires’ disease cases that occurred during the 2014-15 outbreak in Genesee County, Michigan, can be attributed to a change in the City of Flint’s drinking water supply, from Lake Huron to the Flint River.

A comprehensive study

The researchers conducted an exhaustive analysis of data on Legionnaires’ cases in Genesee, Wayne and Oakland counties between 2011 and 2016. FACHEP researchers determined that in 2014-15 an increase in the risk of acquiring Legionnaires’ disease across the Flint water distribution system was consistent with a systemwide proliferation of Legionella bacteria.

The researchers determined that an estimated 80 percent of Legionnaires’ cases during this period were attributable to the change in water supply, according to the article in PNAS.

“During the period when their water was supplied from the Flint River, Flint residents were seven times more likely to develop Legionnaires’ disease,” Zahran said. “After public announcements urging residents to boil their water, there was a lower risk of developing the disease, likely because people avoided using their water.”