As residents of Flint, Michigan continue feeling the fallout from the city’s water crisis, scientists now believe it may be possible to predict the risk for potential outbreaks of Legionnaires’ disease (LD), based on associations they found with decreased levels of chlorine.
NIEHS-funded researchers reported that as the concentration of free chlorine in water delivered to Flint residences decreased, the risk of acquiring LD increased. Collaborators from Colorado State University, Michigan State University, Wayne State University (WSU), and the University of Michigan (UM) published their study Feb. 5 in the journal PNAS.
“These findings provide public health professionals and engineers unparalleled scientific evidence to reduce waterborne disease,” the authors wrote. Senior author Michele Swanson, Ph.D., from UM, led the team.
Water switch coincided with disease outbreak
The 2014-2015 LD outbreak in Genesee County, Michigan was the third largest in American history. Flint is the largest city in that county. Accordingly, the new study took advantage of what scientists refer to as a natural experiment.
“The unprecedented disturbance in water quality within Flint’s drinking water distribution system allowed the evaluation of the statistical relationship between free chlorine residual and Legionnaires’ disease risk within a full-scale drinking water system,” wrote the authors.
The researchers reported a connection between decreased concentrations of free chlorine in water delivered to Flint residences and an increased risk of acquiring LD. Their analyses revealed that free chlorine levels less than 0.5 milligrams per liter or 0.2 milligrams per liter in the city’s water increased the chances that a person would get LD by nearly 3 or 4 times, respectively.
The authors explained that numerous factors affect the availability of free chlorine, including certain chemicals, metals, pH levels, and water temperature. In this analysis, the researchers did not attempt to determine which factor or combination of factors contributed to the decrease in free chlorine during the LD outbreak.
The scientists who conducted this study said that although low chlorine levels might not be the only factor that increases risk of LD, lower levels of free chlorine can be a red flag for conditions that increase the growth of the bacteria that cause this disease.
Grant helped researchers act swiftly
After the water switch, Flint residents complained of foul-smelling, red-colored water — a sign of iron corrosion. They reported rashes, and 87 individuals developed LD. To understand what was going on, scientists applied for funds under a program known as time-sensitive grants.
“Time-sensitive grants are important because they allow researchers to initiate research quickly in response to natural or manmade disasters, or in situations where environmental conditions will change,” said Symma Finn, Ph.D., health science administrator in the NIEHS Population Health Branch.
“In the case of Flint, Michigan, the time-sensitive grant was also used to address the understandable concerns of residents about their exposure to lead, to give them rapid information on how great the risk was and ways they might [reduce or limit] the exposure,” said Finn. While performing the lead study, the researchers were also able to study infectious agents in the water.
Citation: Zahran S, McElmurry SP, Kilgore PE, Mushinski D, Press J, Love NG, Sadler RC, Swanson MS. 2018. Assessment of the Legionnaires' disease outbreak in Flint, Michigan. Proc Natl Acad Sci U S A 115(8):E1730–E1739.
(Frieda Wiley, D.Pharm. is a contract writer for the NIEHS Office of Communications and Public Liaison.)