Health officials are still searching for the source of a serious blood infection linked to at least 18 deaths in the Midwest.

The bacteria, called Elizabethkingia, does not usually cause illness in humans, but in recent months it has sickened dozens and killed 17 people in Wisconsin and one in Michigan.

"This is not a new bacteria, although the strain that seems to be spreading now in Wisconsin is a slightly different one than we're used to seeing," CBS News medical contributor Dr. Holly Phillips explained. "It can cause serious blood infections or meningitis, but generally we see five to ten cases in every state in every year."

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However, since November more than 50 cases have been reported in southern Wisconsin, many of them fatal.

The bacteria got its name from the microbiologist Elizabeth King, who discovered it in 1959. Symptoms of infection include fever, chills, headache, neck pain, and skin infections. Those most at risk for complications are newborns, the elderly, and people with compromised immune systems.

"For people who don't fall into those groups or are otherwise healthy, you'd probably be fine if you contracted it," Phillips said. "But still we need to be extraordinarily vigilant. The average age of the people who have died in Wisconsin is about 77, so it's affecting the older population."

Officials from the Centers for Disease Control and Prevention are still searching for the source. The bacteria typically spreads in health care settings, such as nursing homes, hospitals, and assisted living facilities, but the current outbreak is different.

"We're seeing people who have been in their homes get it, as well as some people who have also been in clinics," Phillips said.

Elizabethkingia can not be transmitted from person to person. Typically, it's spread through water sources.

"But again, it's not following those rules. We're not necessarily seeing it in sinks. We're not necessarily being able to find it in air conditioning. So now the experts are really trying to look at food sources or even personal hygiene products. Things like lotion and toothpaste. They're really trying to turn over all the leaves so they can find out what the source might be," Phillips said.

She noted that the infection can be treated but it is often resistant to most antibiotics."So, probably the main thing the CDC wants to get done is making sure the medical community out there is perfectly aware of this illness so it gets diagnosed quickly and the right antibiotics are started," she said. "The faster it's diagnosed, the faster we can try to figure out what the cases have in common and then try and discover what the source is."