美国国家公共电台 NPR Lethal Pneumonia Outbreak Caused By Low Chlorine In Flint Water（在线收听）

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Scientists announced today that they have figured out the cause of an outbreak of Legionnaires' disease in Flint, Mich., a few years ago. Twelve people died. This was at the start of the city's water crisis. And the problem was a lack of chlorine. NPR's Rebecca Hersher reports.

REBECCA HERSHER, BYLINE: In April 2014, Flint, Mich., switched its water source from Lake Huron to the Flint River. Almost immediately, residents noticed tap water was discolored and acrid-smelling. By 2015, scientists discovered the water was contaminated with lead and other heavy metals. And at the same time, another health crisis was brewing. Dozens of people were getting sick with something called Legionnaires' disease.

MICHELE SWANSON: It is caused by a bacterium - Legionella pneumophila - that normally grows in water.

HERSHER: Michele Swanson has studied Legionnaires' for 25 years at the University of Michigan.

SWANSON: If you don't have a robust immune system, the microbe can really cause a lethal pneumonia.

HERSHER: Usually, Legionnaires' is pretty rare - less than a dozen cases each year in the Flint area. But in 2014 and 2015, there was a huge spike - at least 87 cases and 12 deaths. But it was unclear exactly how the water crisis was connected to the outbreak. Earlier studies suggested the chlorine used to treat the water might have something to do with it. Swanson and her team analyzed detailed data and found, yes, the chlorine level had dropped significantly during the crisis, allowing the Legionella bacteria to thrive.

The results were published today in two papers. And it turns out there was a surprising link between the high levels of lead in the water and low levels of chlorine. Lead and other heavy metals can soak up chlorine. So when the water company in Flint switched to the contaminated source, they would've had to dramatically raise chlorine levels to prevent Legionnaires'.

SWANSON: During the Flint water crisis, the amount of chlorine that needed to be present to reduce the risk of disease was much higher than normal.

HERSHER: That also helps explain why the disease outbreak ended when the city switched back to its original water source, even though the Legionella bacteria aren't completely gone from the water system.

MARC EDWARDS: This sort of research is just essential.

HERSHER: Marc Edwards at Virginia Tech was one of the first scientists to sound the alarm about contaminated water in Flint. He says the new findings may lead Utilities to take more responsibility for preventing future outbreaks.

EDWARDS: Clearly, the Flint water crisis and the deadly Legionnaires' disease outbreak showed that there is a role for the water company to protect consumers.

HERSHER: Rebecca Hersher, NPR News.