Legionnaires' disease (LD), a rare and severe type of pneumonia, is a respiratory infection caused by species of Legionella bacteria. One of the most accurate ways to diagnose LD is to perform culture on samples from a patient's lower respiratory tract, but those samples are difficult to obtain. In addition, growing cultures requires specialized culture media and incubation times and conditions that many laboratories lack; as a result, LD is likely underdiagnosed.