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BOSTON -- The change in water supply from the corrosive Flint River to the colder, cleaner waters of Lake Huron appeared to reduce the ongoing risk of Legionnaire's disease in the city of Flint, Mich., researchers said here.

Only one case of Legionnaire's disease has been reported since March 2016 when Lake Huron water has been used in Flint compared with 91 cases and 12 deaths in the previous 18 months when the drinking water in the city was the Flint River, said , of Virginia Tech University in Blacksburg, and colleagues.

But the city might not be out of the woods yet because cold weather may have suppressed Legionnaire's virulence, his group cautioned in a poster presentation at the ASM Microbe meeting. Also, there was still evidence of Legionella colonization in the city's plumbing so continued vigilance of the water in the city is required.

Intense scrutiny of how politics and financial concerns conspired to make the city's water supply undrinkable, and caused children in the city to be exposed to water with dangerously high lead contamination, may have obscured widespread knowledge of one of the nation's largest outbreaks of Legionnaire's disease.

"Improved water quality could be responsible for decreased Legionella levels throughout Flint, though seasonality might have played a role," Schwake said. "The presence of Legionella strains in large and small buildings indicates potential risk for legionellosis transmission from a variety of sources."

The Flint Water Study team at Virginia Tech found that levels of DNA markers for Legionella have decreased throughout Flint since October 2015 which was before the water change.

"Our city-wide monitoring of Legionella DNA markers has indicated improvement, but in the latest analysis we were able to also culture Legionella and confirmed L. pneumophila Serogroup 1, the most common culprit in Legionnaires' disease, to be viable at some sampling locations in large buildings. Since Legionnaires' disease is more common in warm seasons, it will be important to continue monitoring through summer and for the medical community to be vigilant in diagnosing pneumonia cases," said Schwake.

At one Flint hospital, iron levels in the water dropped from 37.9 parts per billion (ppb) in October 2015 to 7.7 ppb in March 2016, while magnesium levels dropped from 2.1 ppb to 0.5 ppb, and zinc levels dropped from 188 ppb to 100 ppb. Those metals are involved in the growth of Legionella, Schwake explained. On the other hand, levels of copper -- a metal that can prevent bacterial growth -- increased from 257 ppb to 301 ppb, he said.

of Fluid Screen in Cambridge, Mass., said she "had not heard of this large Legionnaire's outbreak," she told 番茄社区app. "I think the work linking corrosion control to Legionella is important. I understand about corrosion from the drinking water perspective, but it is interesting to hear about it from the respiratory pathogen side as well."

Fluid Screen develops assays to detect bacteria detected in water and food sources. Markewich, was not involved in the current study, worked on a Legionnaire's disease in 2015.

"It makes sense that there would be a link to Legionnaire's disease when you think about the iron and other metals that are part of the equation," she said.

Schwake said that for this ongoing study, 42% of the larger sites have been tested and 29% of those sites have tested positive for Legionella species.

"Though Flint is an extreme case, the findings regarding the relationship between corrosion related infrastructure damage and opportunistic pathogen proliferation will have broad relevance," Schwake's group wrote. "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."

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