Two residents of an Illinois veterans' home have died of Legionnaires' Disease, the Illinois Department of Public Health said Friday.

The health department said the two residents at the home in Quincy, about 300 miles southwest of Chicago, had underlying medical conditions. Both were among 23 residents of the facility who had earlier been diagnosed with the disease.

Health department officials said the names of the deceased were being withheld to allow families to notify other family and friends.

On Thursday, state officials said there were eight confirmed cases among residents of the home. That number increased to 23 after tests were conducted Friday.

Legionnaires' Disease is a severe form of pneumonia, with lung inflammation usually caused by infection. It is not transmitted from person to person. Most people get the disease from inhaling the Legionella bacteria.

Adams County Health Department Director of Clinical and Environmental Services Shay Drummond told WGEM-TV that the state health department is recommending elderly people and anyone who sick or has immunity issues should not visit the home. Those groups are most vulnerable to the disease.

The source of the disease has not been determined, but Drummond said the health department is confident it's contained to the veterans' home.

"The Legionella bacteria can be found anywhere, but it's usually in small doses that won't make you sick," Drummond said. "But when a cluster of people get sick like this, it's very likely there's one source point."

Drummond said they hope to the find the source when environmental sampling results come in next week.

An outbreak of Legionnaires' disease in New York City earlier this year killed 12 people and sickened 128. The source was a rooftop air conditioning unit, the city's health commissioner said.

In another possible outbreak, an inmate at California's San Quentin State Prison was hospitalized with Legionnaires' Disease and about 30 other inmates have symptoms, a state corrections spokeswoman said on Friday.