Neil Osterweil

June 18, 2016

BOSTON — There has been only one case of Legionnaires' disease reported since Flint switched back to the Detroit water system after the city's water crisis, marked by a sharp rise in cases of Legionnaires', as well as spikes in blood lead levels in children.

However, evidence of residual pathogenic strains of Legionella suggests public health authorities need to remain on guard for potential new infections.

"We're concerned that, while the water source is better, lingering damage might have caused the system to become permanently more conducive to Legionella," Otto Schwake, PhD, a postdoctoral fellow at the Virginia Polytechnic Institute and State University in Blacksburg, told Medscape Medical News.

Dr Schwake presented his team's findings in a poster session here at the American Society for Microbiology (ASM) Microbe 2016.

In the abstract to their study, Dr Schwake and colleagues acknowledge that although "Flint is an extreme case," it is important to understand "the relationship between corrosion related infrastructure damage and opportunistic pathogen proliferation."

"As water utilities continue to grapple with aging water infrastructure, reduced water demand due to water conservation, dwindling water resources, and poorer water quality, water distribution will become more conducive for the growth and survival of Legionella and other opportunistic pathogens, putting communities at increased risk of contracting disease," they explain.

As previously reported, water from the Flint River is far more corrosive than the Lake Huron water used in the Detroit system. When the city of Flint switched to using the river as a putative cost-saving measure in 2014, the acidic water, which was not treated with necessary corrosive inhibitors, leached lead from the city's aging pipes and plumbing fixtures.

Major Clusters of Legionnaire's During the Crisis

During the crisis, chlorine residuals in the water were low, and microbial growth in the distribution system was high. In the summers after the water switch, there were two major clusters of Legionnaires' disease, with 91 reported cases and 12 confirmed deaths.

For the current study, Dr Schwake and colleagues at Virginia Tech studied water sampled from Flint in October 2015, while river water was still being used, and again in March 2016, after the city had switched back to Detroit water, drawn from Lake Huron. The water was collected from taps in 11 single-story homes and businesses, and from 24 sinks in two large multistory buildings, including a hospital.

For controls, the researchers sampled 14 sites in adjoining Flint Township, a community of similar size and demographics to Flint that continued to use Detroit water when their neighbors switched to river water.

The researchers then tested the water samples for DNA markers for Legionella.

"The idea was that once Flint switched back to the Detroit water source from the not-so-great Flint River, the overall water quality would improve, and this would impact the microbial community, hopefully making all the pathogens we're seeing drop down," Dr Schwake told Medscape Medical News.

Although Legionella levels were generally lower after the city switched back, the study investigators were still able to culture the bacteria. They confirmed the presence of the more pathogenic L pneumophilia Serogroup 1 in three of five homes, and in one of two large buildings.

Although improvement in water quality could explain the decrease in Legionella throughout Flint, it could also be a seasonal effect, said Dr Schwake. This suggests that clinicians and public health authorities should remain vigilant for Legionellosis cases throughout the summer as conditions become more favorable for bacterial growth.

A microbial researcher who was not involved in the study told Medscape Medical News it would also be important for the investigators to look for the presence of acanthamoeba in water samples.

"They're looking for traces of Legionella, and they found Legionella, but they did not look for the free-living amoebas that are reservoirs for that. If they were to look for that, perhaps they could find the reservoir seeding the remaining Legionella there," said Darlene Miller, DHSc, MPH, from the University of Miami Bascom Palmer Eye Institute.

"Perhaps the concentration of chlorine is not high enough to eliminate acanthamoeba," she added.

The study is ongoing, and Dr Schwake told Medscape Medical News that pending additional funding, the researchers plan to test the samples for acanthamoeba, as well as Pseudomonas, mycobacterium, and other waterborne pathogens.

This study was supported by grants from the National Science Foundation and the Alfred P. Sloan Foundation. Dr Schwake and Dr Miller have disclosed no relevant financial relationships.

American Society for Microbiology (ASM) Microbe 2016: Poster presented June 17, 2016.

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