Learning from Flint: Legionnaires’ Disease Studies Show a Need for Careful Water Treatment and Better Patient Testing Everywhere

Two new research studies provide crucial health lessons from the water crisis in Flint, Michigan — lessons that affect not only the people of the city and its suburbs, but also communities far beyond.

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Both concern Legionnaires' disease, the pneumonialike lung infection caused by bacteria called Legionella pneumophila. The studies are published in two major scientific journals by teams from the University of Michigan, Colorado State University and Wayne State University.

Link between Legionnaires' cases, water changes and low chlorine

One study shows that in the months after the city's water supply started coming from the Flint River in April 2014, city residents had seven times the chance of being diagnosed with Legionnaires' disease.

"After public announcements urging residents to boil their water, there was a lower risk of developing the disease, likely because people avoided using the water," says lead author Sammy Zahran, Ph.D., an associate professor of demography and epidemiology at Colorado State University who co-directs the university's Center for Disaster and Risk Analysis.

The disease risk returned to normal levels when the city resumed using Lake Huron water in 2015. In all, the Flint area recorded 87 cases of the disease, the third-largest U.S. outbreak in history.

The research, published in Proceedings of the National Academy of Sciences, shows that within the city, the risk of Legionnaires' disease was higher in areas with lower levels of free chlorine in the water. Legionella bacteria are less likely to survive in water with high free chlorine levels because it is toxic. But high levels of iron and organic matter in corroding water pipes — an issue with older infrastructure — both feed Legionella and neutralize chlorine.

Many communities in the U.S. and beyond treat their water with chlorine. They also use other water-treatment chemicals to protect pipes from corrosion, which can send iron, lead and other metals into the water. So the new results show the importance of careful water monitoring and treatment everywhere.

The study also casts doubt on the theory that Flint-area residents caught Legionella only if they were treated in a particular hospital. Even when the investigators excluded cases from that hospital, they still saw a strong link between the citywide water changes and Legionnaires' cases.

They also found that the risk of Legionnaires' disease in Flint suburbs varied based on the number of people from each community who commuted into the city for work.

Mismatch between bacteria in homes and what doctors test for

Published in mBio, the second study adds new evidence to the growing sense that many cases of Legionnaires' disease go undetected. Although a more precise diagnosis may not change the way patients' pneumonialike symptoms are treated, it may hinder finding and tracing the source of outbreaks such as the one in Flint.

The researchers tested 130 Flint homes, plus 51 homes elsewhere in Genesee County, for Legionella in tap water and water heaters. They found it in 12 percent of the homes and grew that bacteria in the laboratory. Through detailed DNA analysis, they found that the homes had different strains, or subtypes, of the bacteria than what had been detected in hospital patients.

Most of the Flint Legionella samples, which were gathered a year after the city's water supply was returned to Lake Huron, were a variety called serogroup 6. But the hospital cases showed Legionella serogroup 1.

This mismatch is likely because doctors have a simple urine test for Legionella serogroup 1, and they use it on hospitalized patients to figure out what's causing their pneumonialike symptoms. But that test can't detect serogroup 6. Only a slower test, which requires growing or "culturing" bacteria from the phlegm from patients' lungs, can see it. Most patients never receive such a test.

The researchers took the serogroup 6 samples and grew them in the laboratory to compare them with bacteria from patients diagnosed with serogroup 1. In a lab dish, serogroup 6 was just as capable as serogroup 1 of infecting immune-system cells called macrophages, they found. In the human body, Legionella infects macrophages in the lungs, where it reproduces before bursting out and triggering the disease's symptoms.

Although researchers found Legionella serogroup 6 in homes, they do not know yet if it can survive in the tiny water droplets called aerosols that serogroup 1 bacteria are known to thrive in. Such droplets — for example, from a shower — are the main way Legionella gets into the lungs.

The researchers also can't tell if there were additional, undetected cases of Legionnaires' disease in the Flint area after the water supply change. They hope to study this in the future. Meanwhile, they hope the findings will inform the growing body of evidence that more detailed testing of patients with suspected Legionnaires' disease is needed to spot and stop outbreaks and to address the source.

"Since Legionnaires' disease typically has a single-point source that could infect others, it's more important to get detailed information about strains and perform the epidemiological work that can determine if cases are related," says Michele S. Swanson, Ph.D., a University of Michigan microbiologist and longtime Legionella researcher and the corresponding author of both new studies. The lead author of the mBio study is Brenda Byrne, a member of Swanson's laboratory team.

Swanson notes that Ontario doctors now routinely order the more complicated culture of phlegm specimens for patients who may have Legionnaires' disease.

That kind of detective work, for instance, happened in Pontiac, Michigan, in 1968, when public health officials worked together to determine that Legionella bacteria had sickened more than 100 people who worked in or visited a county health building.

To this day, mild cases of the disease are referred to as "Pontiac fever."

More information

Both studies include as authors Shawn P. McElmurry, Ph.D., P.E., and Paul E. Kilgore, Ph.D., co-directors of the Flint Area Community Health and Environment Partnership (FACHEP), a research effort based at Wayne State University that is evaluating the possible association between changes in Flint's water system and public health. Nancy Love, Ph.D., P.E., BCEE, a U-M engineering professor, is a co-author and FACHEP team member.

The research was sponsored by FACHEP's contract with the Michigan Department of Health and Human Services and by the National Institute of Environmental Health Sciences of the National Institutes of Health.

The researchers credit Flint residents for their essential roles in the research project, including those who opened their doors to the research team for water sampling and those who worked in the FACHEP field office in Flint, helped to coordinate the surveillance campaign and assisted in other ways.

Photo credit: CDC Public Health Image Library