Health officials warn of 'large' outbreak of serious bacterial illness in Florida

The cases of meningococcal disease are primarily in men who have sex with men, the CDC said.

Health officials are warning Florida residents about a "large" outbreak of a potentially fatal bacterial illness known as meningococcal disease that's primarily affecting gay and bisexual men.

So far this year, there have been 21 confirmed cases of meningococcal disease as of Monday, according to Florida Department of Health data. That's higher than the state's five-year average of cases of the disease.

"[Florida Department of Health] epidemiologists are investigating each case as well as contacting people with potential or direct exposure to known cases to provide them with information and treatment options," the department said in a statement.

Most of the cases are in central Florida, and more than half are in people between the ages of 20 and 39, according to state health department data.