(CNN) Wisconsin health officials are warning residents about an outbreak of Elizabethkingia, a rare blood infection that has sickened dozens in the state.
Authorities have discovered the bacteria in 44 people since November, the Wisconsin Department of Health Services said this week. Eighteen of them have died.
Individuals with compromised immune systems or serious underlying health conditions are more at risk for this illness. Officials said most of the patients are over age 65 and have histories of underlying health conditions.
"It has not been determined if the cause is the bacterial infection, or the patients' other serious health conditions, or both," according to a statement from the state health department.
Symptoms include shortness of breath, fever, chills and cellulitis. A laboratory test is needed to confirm infection.
"Elizabethkingia are bacteria that are rarely reported to cause illness in humans, and are uncommon colonizers of the respiratory tract," the statement said.
A team from the Centers for Disease Control and Prevention is in Wisconsin working with state health officials to investigate this outbreak, according to CDC spokesman Tom Skinner. The agency is also conducting tests on environmental samples being sent from Wisconsin to its Atlanta lab.
The number of people known to be infected is expected to rise as more cases are identified and confirmed.
The bacterium is named after American bacteriologist Elizabeth King, who discovered it in 1959.