Legionnaires' disease is a serious type of pneumonia caused by bacteria known as Legionella.

According to the Centers for Disease Control and Prevention, Legionnaires' disease can cause pneumonia symptoms including cough, shortness of breath, muscle aches, headache and fever. 

Doctors use chest x-rays or physical exams to check for pneumonia. 

While Legionnaires' disease is serious, it can be treated with antibiotics. Most people who get sick need hospitalization, but make a full recovery.

On Monday, the Sheraton Hotel in downtown Atlanta decided to close after multiple cases of the disease was reported there.

The Fulton County Board of Health is investigating the reported cases and working with the Georgia Department of Public Health. 

In 2016, four employees at Lockheed Martin came down with the disease over a 12 month period.