Cases of Legionnaires' disease have been appearing across the United States in the past few weeks.

Four Florida gym-goers fell ill after coming into contact with contaminated water, two hotel guests in Last Vegas contracted the lung infection and New York City police officers were warned against showering at their station due to the disease.

The outbreak is concerning because of the warmer season when people are more likely to head to public swimming pools and use the showers and hot tubs, where most cases occur.

The potentially fatal disease is a severe form of pneumonia and develops when people breathe small droplets of bacteria-infected water. 

Although contracting Legionnaires' is rare, there has been a 450 percent increase of cases in the past two decades, according to a new CDC report.

The news comes on the same week Nick Lyon, head of the Michigan health department, was charged with involuntary manslaughter for the Flint water crisis, where at least one person died of Legionnaires' disease.  

The outbreaks follow a pattern of concerning news to America's water supply as a report in May revealed that nearly 30 million people have contaminated tap water.

The hotel released a statement on June 9 confirming the outbreak and said it was intensely cleaning, using Chlorine at high temperatures to disinfect the rooms.

New York City was the next area to fall victim when a police officer was diagnosed with the sickness and officers were advised not to shower at the East Harlem station.

Although the police officers were told they could still use cold water to cook and drink, several were on edge about drinking any water there, according to reports.

The Florida Health Department confirmed on Tuesday that four people became sick and all were members of two separate LA Fitness gyms in the Orange County area.

Health officials said showers and spas at both locations were in need of a disinfecting treatment with a hydrochlorinated solution.