(CNN) A new cluster of Elizabethkingia infection, previously rarely seen in humans, has been found in Illinois, health officials said Wednesday.
Testing by the U.S. Centers for Disease Control and Prevention confirmed the Elizabethkingia anophelis infection in 10 Illinois residents, according to the Illinois Department of Public Health. Six of those individuals have died. Most of the infected patients had underlying health conditions, and it's unknown if they died from the infection or pre-existing conditions.
The Illinois cluster of cases is a different strain of infection from the one identified in an ongoing Elizabethkingia outbreak in Wisconsin, first reported in March. Fifty-nine cases have been confirmed in that state since November. Eighteen have died. Officials there have said all of those infected had "at least one serious underlying illness" and most are older than 65. The cases began in 2014.
Dr. Chris Braden, deputy director at the CDC's National Center for Emerging and Zoonotic Infectious Diseases, said this cluster of cases in Illinois is not surprising but it is concerning.
Federal and state health officials asked health care providers and health departments to be on the lookout for cases of Elizabethkingia last month. These bacteria are not mandated or voluntarily reported so clusters may have previously gone unnoticed.
"We are identifying this because Illinois really looked for it," Braden said.
Last week the Illinois Department of Public Health said it found one case of the same strain of Elizabethkingia identified in the Wisconsin outbreak. That person died earlier this year.
Last month health officials in Michigan also found a case of the infection that matched the strain of the Wisconsin outbreak.
"Although this strain of Elizabethkingia is different than the one seen in the Wisconsin outbreak, our investigatory methods remain the same and we continue to work with the CDC and our local health departments to investigate this cluster of cases and develop ways to prevent additional infections," said Dr. Nirav Shah, director of the Illinois Department of Public Health.
The bacteria are commonly found in soil, river water and reservoirs but do not commonly cause illness in humans. People with compromised immune systems or serious underlying health conditions are more at risk of infection. Previous outbreaks have been associated with health care settings. Most of the infections have been in the bloodstream, although some have been in the respiratory system or joints.
Symptoms of Elizabethkingia infection include fever, shortness of breath, chills and a bacterial skin infection called cellulitis. The infection is often antibiotic resistant and difficult to treat.
Health officials have not yet found the source of the Wisconsin outbreak. Braden said the Illinois investigation is starting by gathering information about each individual case, including where the person lived, what health care they were receiving and what facilities they had been to.
It will also consider what type of infection the person had -- for example, was it in the bloodstream or on the skin? Because the strains are different officials are operating under the assumption the Illinois and Wisconsin cases are unrelated. However, there is a possibility that the investigation could find they are related -- for example, exposure to the same product.
"Previously, health providers were not required to report individual cases of Elizabethkingia, so it is difficult to determine the degree and kind of exposure that results in illness. For the same reason, it is difficult to estimate how many cases of illness actually occur each year," a statement from the Illinois health department said.
Braden said, "We haven't really been looking for clusters with this particular organism; it's possible we could see others as states request laboratories look for these and request them."
With the source still under investigation, health officials said the best way to prevent this and other infections is to follow "good health practices," including frequently washing hands and requesting health care providers do the same.