The state is investigating a case of Legionnaires’ disease, a potentially deadly form of pneumonia caused by a bacterial infection.

The Oahu individual with the bacteria known as Legionella is being treated at The Queen’s Medical Center as Health Department officials investigate how the person contracted the disease, primarily spread through inhaling aerosolized water droplets. The bacteria occurs naturally in freshwater lakes and streams, but is a public health concern when spread in building water systems like showerheads and faucets, hot tubs and cooling systems.

It is the sixth case this year. The state has seen an average of 10 cases annually in the past five years.

“These cases have been isolated and unrelated and not clusters or groups of people who became ill. They are single individual cases,” DOH spokeswoman Janice Okubo told the Honolulu Star-Advertiser. “Occasionally we do get these cases. It’s not something unusual and out-of the-ordinary but we do investigate every case to see if we can determine a source. Whenever you get pneumonia it can be very serious.”

No further details were available, but additional information may be released by the end of this week, she said.

The people most at risk are those with chronic diseases and already compromised immune systems, smokers and the elderly, according to the DOH.

“The Queen’s Medical Center is investigating the case of one patient who has presented with symptoms consistent with a Legionella infection, which is most likely to occur in immunocompromised hosts,” Dr. Leslie Chun, Queen’s chief medical officer and chief quality officer, said in a statement. “It is not readily transmissible from person to person. We are investigating potential sources.”

Dr. Heidi Hillesland, infectious disease specialist and internal medicine physician at Wilcox Medical Center on Kauai, said the lung infection has symptoms of fever and cough similar to other types of pneumonia. Common symptoms include shortness of breath, vomiting and diarrhea, as well as low sodium levels and liver inflammation.

“The infection can range to very mild to severe. Older age and lung disease like COPD (chronic obstructive pulmonary disease) are factors that can make the infection worse,” she said.

The bacteria can contaminate soil and water with large outbreaks occasionally in tainted building water systems. The disease was named after a major outbreak in the 1970s in Philadelphia following an American Legion Convention where it was later identified that the hotel had a contaminated air conditioning system.

Patients with the potentially fatal condition may be treated with antibiotics commonly used for pneumonia.