An outbreak of Legionnaires' disease cases linked to a Florida gym has brought cases to a 10-year-high in the state.

The Orange County "gym exposure" outbreak includes 14 cases of the disease, the Florida Department of Health said.

Legionnaires' disease is a serious type of pneumonia caused by the Legionella bacteria, according to the health department. The lung infection can be mild for healthy people but serious and sometimes deadly for certain at-risk groups.

"The most common way for someone to get sick is by breathing in mist containing Legionella," according to the U.S. Centers for Disease Control and Prevention.

The gym outbreak brings the total number of cases in Orange County in 2025 to 82, the highest in the state. Florida reported a total of 72 confirmed legionellosis cases in November. Florida has seen 665 cases in 2025.

Previously: An obscure disease keeps spreading through air conditioning

Legionellosis case reports also include Pontiac fever, which is a milder infection caused by the same type of Legionella bacteria that causes Legionnaires' disease.

Florida’s uptick in Legionnaires' cases mirrors a national trend, according to the U.S. Centers for Disease Control and Prevention. Here's what to know about the illness:

What is Legionnaires' disease? What are the symptoms?

Most healthy people exposed to Legionella don't get sick or exhibit the milder Pontiac fever. Older adults and people who smoke have a higher risk of contracting the more serious Legionnaires' disease cases and should seek immediate treatment.

The first signs of Legionnaires' disease tend to mimic the flu. People often develop a high fever, headaches and muscle aches between two and 10 days after contact with Legionella bacteria, according to the Mayo Clinic.

A day or two afterward, people who have contracted Legionnaires' disease often report a cough that might bring up mucus and sometimes blood, shortness of breath, chest pain, nausea, vomiting, diarrhea, confusion or other mental changes.

How does Legionnaires' disease spread?

Legionella bacterium thrive in warm, aquatic environments and are usually spread through aerosolized water that is then inhaled, such as in showers and spas. Cooling towers, water systems found on top of buildings that control the temperature of cooling systems like air conditioning, can also be a source of spread.

It is not transmitted person-to-person, according to the Florida Department of Health. Rather, Legionnaires' disease is usually caught when someone inhales water droplets that are contaminated with Legionella bacteria.

The CDC estimates about nine in 10 outbreaks are caused by problems that could have been prevented with effective water management, including for hot tubs, plumbing systems and cooling towers.

Is Legionnaires' disease fatal? Who is most at risk?

About one out of every 10 people who get sick with Legionnaires' disease dies from complications related to the disease, according to the CDC.

"For those who get Legionnaires' disease during a stay in a healthcare facility, about 1 out of every 4 will die," the CDC website says.

Current or former smokers, people 50 years old or older and people with certain health issues or conditions are at higher risk of getting sick. Those conditions include:

• Cancer

• Chronic lung disease

• Diabetes

• Kidney failure

• Liver failure

• Weak immune system

CDC data also show that some groups of people and factors have higher incidence rates:

• Black people

• Males

• Older adults

• Northeast and Midwest regions

• Summer and fall months

US cases of Legionnaires' disease on an uptick

Since 2000, the United States has seen legionellosis rates increase ninefold. Reports peaked in 2018 and dropped to a five-year low during the COVID-19 pandemic in 2020. Reported cases rebounded in 2021 and are on the rise again.

Between 8,000 and 18,000 people are hospitalized with Legionnaires' each year in the United States, Florida's health department said.

The CDC is investigating a 2025 Legionnaires' cluster in New York City that has been blamed for at least seven deaths, 90 hospitalizations and 114 cases over the summer. The outbreak is suspected to be caused by cooling towers harboring the bacteria in central Harlem.

The Harlem cases sprang up in late July and prompted officials to work to remediate issues with a dozen cooling towers across five zip codes. Officials declared the cluster over on Aug. 29.

Climate change has been pointed to as a contributing factor in increasing Legionnaires' cases; hotter and more humid conditions mean more places are adding cooling infrastructure that can breed bacteria.

Contributing: Eduardo Cuevas, USA TODAY

This article originally appeared on Pensacola News Journal: Florida Legionnaires' outbreak blamed on 'gym exposure'