CSU researchers find cause of Legionnaires' disease outbreak in Flint

An 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 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 system-wide 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."

"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 water decreased," said Shawn McElmurry, associate professor of civil and environmental engineering at Wayne State University and the FACHEP principal investigator. "Since municipalities routinely measure free chlorine at multiple points in water distribution systems to reduce the risk of waterborne illnesses, these results should help inform future water management policies and practices." Chlorine is routinely added to drinking water to kill microbes.

EFFECT OUTSIDE FLINT

During the water crisis, the likelihood of Legionnaires' disease occurring in communities adjacent to Flint also increased, probably due to the number of people who commuted into Flint.

After the city returned to its original water source, Lake Huron, the risk of a Flint neighborhood presenting with Legionnaires' disease returned to historically normal levels.

The analysis also suggested that chlorine residual levels recommended by regulatory agencies (0.2 or 0.5 parts per million) may not be sufficient to protect communities from Legionella pneumophila exposure when water quality conditions support strong Legionella growth. These were the conditions in Flint during and immediately after the water change.

"It's gratifying to have independent confirmation of what many of us working and living in Flint have suspected," said Dr. Lawrence Reynolds, a member of Michigan Gov. Rick Snyder's Flint Water Advisory Task Force and the Flint Water Interagency Coordinating Committee. "This provides clarity regarding what happened in this community and hopefully will help others. "

A DIFFICULT TASK

McElmurry noted that the investigation was challenging. "These are very complicated questions, and we are working with a very talented team of investigators including epidemiologists, infectious disease specialists, microbiologists, water engineers, social-behavioral scientists and statisticians to understand what happened in Flint," he said. "Most important was the assistance of residents who worked directly with us on this challenging problem."

Before making their results public, Zahran and his co-authors subjected their analysis to a peer-review process. That process for research published in academic journals helps verify that the methods and conclusions have been evaluated by experts in the field and meets rigorous standards for accuracy. Research and the peer-review process takes time.

"While we have been anxious to share these results as soon as possible, we thought it was also important that our research was subjected to the highest level of independent review," said McElmurry. "Peer-review allows us to demonstrate that our work is independent and free of any external influence."

The FACHEP research team is a consortium led by Wayne State University that includes the University of Michigan, Michigan State University, Kettering University, Colorado State University and the Henry Ford Health System.

ABOUT THE PROCESS

The FACHEP team collected water samples from more than 368 randomly selected homes in Flint, including 136 homes in 2016 and 221 homes in 2017. It also collected samples from 268 randomly selected homes in Genesee County, including 51 homes tested in 2016 and 217 homes tested in 2017.

Samples collected in Genesee County outside of Flint, and in Wayne County, will serve as comparisons to Flint samples to better understand water quality in the city.