By Stephanie Stahl

PHILADELPHIA (CBS) — Hotel guests could have been exposed to Legionnaires’ disease and not even know it. The outbreak in Atlanta has led to a lawsuit that was filed Monday.

Legionnaires’ disease can feel like a case of the flu and it can be tricky to accurately diagnose, which is important because antibiotic treatment is critical.

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The investigation on the newest outbreak in Atlanta centers on people who stayed there in mid-July.

The latest Legionnaires’ disease outbreak has been identified at the Sheraton Atlanta. One person has died and a dozen have tested positive.

“I couldn’t sleep, didn’t want to eat, couldn’t drink because everything was horrible. I was delirious,” said Germany Greer, who contracted the disease.

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Legionnaires’ disease is a severe form of pneumonia. People get sick inhaling by microscopic water droplets containing the Legionella bacteria. It is not contagious.

“This is one of those bugs that lives out in the environment amongst us, and on occasion, it gets into a man-made water system, contaminates it and can be very hard to get rid of when that happens,” said Dr. William Schaffner, with Vanderbilt University Medical Center.

Legionnaires’ disease was first identified here in Philadelphia in 1976 when a mysterious respiratory illness spread through a legionnaires convention that was meeting at the Bellevue-Stratford Hotel.

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Since then, there have been a series of outbreaks, here and around the country. The CDC says one in 10 Legionnaires’ victims will die.

With the latest case in Atlanta, attorney Chris Stewart represents 40 Sheraton guests with confirmed or presumptive cases of Legionnaires’ disease.

“This is a massive problem nationwide. People don’t know they’re sick yet with Legionnaires’ disease,” Stewart said.

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In a statement, the hotel offered its “deepest sympathies to all those affected,” adding, “a thorough cleaning of the hotel’s entire water distribution system has been completed, including scrubbing and chlorination.”

The hotel remains closed. The outbreak is the largest ever recorded in Georgia.

Health officials who are examining when people may have been exposed are looking at a timeline that lasts more than a month.

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The disease is usually associated with the water or air systems in big buildings — not something you’d find in someone’s home.

Stephanie Stahl