Updated

Wisconsin officials have revised down to 15 the number of deaths that may be related to an outbreak of Elizabethkingia bacteria that has infected a total of 48 people, most of them elderly, over the past five months.

Earlier, the state said there were 18 deaths possibly linked to the bacteria, but it revised the figure lower due to unconfirmed Elizabethkingia infections, duplicate reports and other issues, the Wisconsin Department of Health Services said in a statement.

The outbreak of the rare infection in southeastern and southern Wisconsin between Nov. 1 and March 9 has mostly affected patients older than 65 who have a history of at least one underlying serious illness.

"This (15) is the number of people with confirmed Elizabethkingia infections, who later died," the statement said. "It has not been determined if these deaths were caused by the infection or other serious pre-existing health problems."

Investigators from Wisconsin and the national Centers for Disease Control are looking into possible sources of the outbreak of the bacteria, which is rarely reported to cause illness in humans and can sometimes be found in the respiratory tract.

The CDC has eight disease detectives in Wisconsin helping with the investigation, as well as laboratory staff in headquarters in Atlanta.

The experts have tested samples from potential sources including healthcare products, water sources and the environment, but so far have not found a source for the infection, the CDC said in a statement on Thursday.

Symptoms of Elizabethkingia infection can include fever, shortness of breath, and chills or cellulitis. Confirmation of the illness requires a laboratory test.

(Reporting by Fiona Ortiz in Chicago; Editing by Bernadette Baum)