By Stephanie Stahl

PHILADELPHIA (CBS) — A medical mystery is being investigated in Montgomery County to learn more about a lung infection that has been linked to water. The disease is called Nontuberculous Mycobacteria or NTM.

It’s a lung infection, similar to tuberculosis, that is caused by a bacteria found mainly in water but also in soil and in the air. Doctors say NTM is rare but the number of patients is growing.

The unlikely victims are white, thin, post-menopausal women who live in affluent neighborhoods around Philadelphia’s Main Line. “This is being researched very intensively right now,” says Dr. Leah Lande, a pulmonologist at Lankenau Medical Center which is part of Main Line Health.

“This is in all of our water,” she says. “We are exposed to it everyday when we take a shower.”

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Dr. Lande doesn’t want to cause unnecessary hysteria and emphasizes that the lung infection is very rare. She says she treats about 100 patients a year. Symptoms include a cough and fatigue.

A study from the American Thoracic Society and the National Institutes Of Health in 2012 identified 7 significant clusters of NTM around the country. One of the clusters was found in the greater Philadelphia metropolitan area where significant clusters were identified in Montgomery County.

“You’re thinking, have you hurt yourself by drinking water,” says Karen McCarthy. Karen, who lives in nearby West Chester, was diagnosed with NTM in May.

She’s being treated with antibiotics until next September and has installed a special water filter in order to avoid re-exposure. NTM causes the 54-year-old to struggle with fatigue and respiratory issues.

But Karen makes sure to stay in shape which ironically made her more susceptible.

She says she was shocked when she found out that being healthy and fit can put you are risk for the disease.

The NIH report also noted that most NTM patients had higher education and income levels. The infection is difficult to identify. “The diagnosis is tricky, it is often delayed,” says Dr. Lande. “I will see patients as well as others that have been undiagnosed for several years.”

Dr. Lande says mycobacteria can be especially dangerous when it’s aerosolized in the shower or from a humidifier and even with dirt that blows in the air. Philip Leitman had never heard of NTM but he says he learned about the lung infection fast after his wife Fern was diagnosed.

They lived in another NTM hot spot in Florida. The lung infection eventually killed her.

“She was such an amazing person,” said Philip. “But she is in my heart and with our children in their hearts and with our grandchildren.” He started an online NTM support group. But not everyone is at risk.

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Doctors say African-Americans and people who are heavy tend to not get NTM even though the bacteria that causes it is everywhere.

So why do only certain people develop the infection? “We don’t know,” says Dr. Lande. “A lot of people are trying to figure that out now but that’s not really understood right now.”

Aqua Pennsylvania ,which supplies water to our area, says it doesn’t test for the bacteria because it’s not a regulated contaminant and there is no EPA-approved method to measure it.

Switching to bottled water isn’t necessarily the answer because the bacteria can be in so many places, but it only causes problems for an unfortunate few.

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