HONOLULU - Legionnaires' Disease is a severe form of Pneumonia that just claimed a life.

There's been four recent cases on Oahu, all involving patients over the age of 50, each with serious underlying medical conditions.

Of those: one died and one recovered. What's not known is exactly where each contracted the disease.

"The patient who died was one of those community on set cases, in which the patient had symptoms of Pneumonia at the time of admission, so they presumably got the infection before they arrived in the hospital," Dr. Erlaine Bello, Queen's Medical Center said. 

Two others remain in the hospital at Queen's Medical Center, where a Department of Health investigation is looking at if the water is to blame. 

"The focus right now is very much on the hospital and its especially because of the high risk patients that they have here. We want to make sure everyone is protected," Dr. Sarah Park, state epidemiologist said. 

Legionella bacteria causes Legionnaires' Disease and is naturally found in freshwater, but can become a health concern when it gets into to man-made water systems such as showers, fountains and cooling systems.  

People with weakened immune systems are more at risk and can contract it by breathing in bacteria from contaminated water in a spray or mist form.

Water samples have been collected at Queen's but DOH says those results may take some time. 

"We definitely sampled water on the units were the patients who have Legionella were housed. We're also doing random samples throughout the hospital where we think other high risk patients might be," Bello said. 

In the meantime, Queen's says it has since taken action to keep its high-risk patients protected.

"Those are cancer patients, people with sever underlying lung disease, transplant patients that they limit their exposure to tap water so we've provided alternative water sources, bathing sources for them," Bello said. 

The medical center says it also has replaced its faucets and in creased chlorination testing of its water. Queen's and DOH are actively investigating all potential sources within and outside of the hospital.