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New Research Investigates Legionnaires Outbreak in Flint

Sam Dorevitch headshot.

In 2017 the State of Michigan asked KWR, a Dutch clean water research institute, to investigate the epidemic of Legionnaires’ Disease in Genesee County, Michigan in 2014 and 2015.  The School of Public Health’s Dr. Samuel Dorevitch, professor of environmental and occupational health sciences, was asked to join the research team.

Legionnaires’ disease is a severe kind of pneumonia (lung infection) caused by the bacteria Legionella pneumophila. These bacteria can grow in warm water systems and become airborne in showers, cooling towers, and air conditioning systems. People typically catch it by breathing in air with tiny water droplets (called aerosols) that contain the Legionnaires’ disease bacteria.

An outbreak of Legionnaires’ disease occurred in 2014-2015 among people who lived in Genesee County, Michigan, which includes the City of Flint. A total of 86 residents of Genesee County developed Legionnaires’ disease. Most of the people who developed Legionnaires’ were age 65 or older and had a chronic health condition.  The research team found evidence for three sources: strong evidence for exposure to a Flint hospital in 2014 and 2015, and weaker evidence for exposure to City of Flint water at home or living in the proximity of a specific cluster of cooling towers, both only in 2014. The research is published in the scientific journal Environmental Health Perspectives.

The research team travelled to Lansing and Flint and studied the information that was available about the Legionnaires’ disease epidemic in Genesee County in 2014 and 2015. The team evaluated medical records, disease and death statistics, Census data, address data, water connection and use data, hospital data, Flint water data, geographical data, and weather data.

Nearly half of those who contracted the disease had been in the McLaren Flint Hospital before they got sick with Legionnaires’ disease. Most of these 42 people had been hospitalized, but some of them were visitors or outpatients. The study identified strong evidence that people in Genesee County got sick with Legionnaires’ disease because of their contact with this hospital:

  • More cases had contact with this hospital than would be expected if this was coincidence;
  • Legionella pneumophila was present in the plumbing system of the hospital, during the outbreak period and, in some samples tested, in high concentrations;
  • Using advanced genome testing, Legionella pneumophila strains from the hospital’s plumbing system were highly similar to strains that were isolated from people who had been in the hospital with Legionnaires’ disease;
  • Right after the hospital implemented effective Legionella control with superheating/ chlorination and monochloramine no new cases of Legionnaires’ disease occurred among people who had been at this hospital.

The study also indicated the Flint water supply may be associated with the disease outbreak.  Of the 86 people who came down with Legionnaires’ disease, 29 had City of Flint water service at their homes during the outbreak. Some of these people had also been at the Flint Hospital before they came down with Legionnaires’ disease. Researchers observed that residents on City of Flint water had a higher risk of acquiring Legionnaires’ disease than Genesee County residents that were not served by City of Flint water in 2014. However, this was not the case in 2015.

Finally, people living closer to a cluster of cooling towers in Flint had a higher risk of acquiring Legionnaires’ disease in 2014, but not in 2015. Of the 86 people who became sick with the disease, only a small number of people may have gotten exposed to Legionella pneumophila at their homes through aerosols coming from any of a cluster of five cooling towers. Some of these people had also been at the hospital before they came down with Legionnaires’ disease.

Dorevitch says the sheer volume of public health challenges in Flint at the time of the outbreak may have challenged a prompt, effective public health response to the Legionnaire’s disease outbreak.

“It’s well known that egionnaires disease can cause outbreaks in hospital, that’s not new,” Dorevitch said.  “In Flint, there was the lead crisis, loss of drinking water because of the lead crisis, a lot of appropriate anger and distrust, and the situation had political dimensions. In some ways these factors may have contributed to a situation where a textbook outbreak investigation was difficult to conduct.”

From a practice perspective, Dorevitch says the study illustrates the need to strengthen the communication process between healthcare delivery systems and public health agencies.

“An effective public health response depends on effective communication, trust and common goals all around,” Dorevitch said.  “In an ideal setting, hospitals, the local health department, the state health department, and if needed, the CDC, would all be working together.”