It can take up to 10 days for symptoms to appear, and when they do, they initially look like a bad case of flu. The illness typically begins with a high fever, a cough, shortness of breath, muscle ache and headache. After a couple of days, these symptoms progress to pneumonia, a buildup of fluid in the lungs that makes it difficult to breathe. In 2014 and 2015, more than 95% of people with Legionnaires’ disease wound up being hospitalized. While the disease is treatable with antibiotics, about 1 in 8 still died from their infection.
Although the bacteria can infect people of all ages, more than 80% of reported cases were 50 years old or older and about 60% were men. Smokers and people with underlying lung diseases – such as emphysema or chronic obstructive pulmonary disease – or weakened immune systems, due to medicines or health problems such as cancer or diabetes, are also at higher risk of infection.