The Elizabethkingia anophelis bacteria was first identified in 1959, but health officials still know little about it.

Twenty people in the Midwest have died after becoming infected with the Elizabethkingia anophelis bacteria in an outbreak that has stumped public health officials since November.

Officials at the Centers for Disease Control and Prevention (CDC) confirmed that 61 individuals have tested positive for the bacteria as of April 13.

Fifty-nine of those infected are from 12 neighboring counties in southeastern Wisconsin, with one case in Lake Villa, Illinois, and another in western Michigan.

The majority of those infected is over age 65 and has at least one serious underlying health condition. In the 20 cases that resulted in death, health officials were unable to determine whether the cause was the bacterial infection, the underlying condition, or a combination of the two.

“Although Elizabethkingia is a common organism in the environment (water and soil), it rarely causes infections,” Dr. Christopher Braden, director of the Division of Foodborne, Waterborne, and Environmental Diseases in CDC’s National Center for Emerging and Zoonotic Infectious Diseases, told Healthline via email. “About 5 to 10 cases per state per year are reported in the United States.”

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Historically, Elizabethkingia infections are not found in healthy individuals.

Instead, they may cause meningitis infections in newborns or bloodstream infections in those with compromised immune systems.

The gram-negative organism is named for Elizabeth O. King, who discovered it in 1959.

Elizabethkingia bacteria are usually resistant to many of the drugs doctors traditionally use to cure infections. However, there are other antibiotics effective in treatment.

Early detection of the infection is key in making sure treatment is successful.

Epidemiologists have determined that the genetic material isolated from current outbreak samples is nearly identical, meaning that there is likely a single source of infection.

Officials have not yet determined the source of the bacteria. Each case discovered so far is within 100 miles of Lake Michigan’s border.

The commonality essentially ends there. CDC “disease detective” teams made up of epidemiologists, physicians, and statisticians have explored numerous potential sources and come up with no conclusive source of infection.

“Epidemiological, microbiological, and distribution information for medical and personal care products, water sources, and food products has not provided evidence that any one of these is the outbreak source to date,” Braden said.

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The CDC and state health departments in Wisconsin, Michigan, and Illinois are working to determine any possible common exposures of those infected.

Braden notes that outbreak investigations include “interviews with patients and family members, evaluations of patients’ home and healthcare environments, and laboratory testing of environmental samples.”

While Elizabethkingia anopheles was originally isolated in a mosquito species, there is no evidence that it can be transmitted from mosquitoes to people.

Although Lake Michigan does appear to be the common geographic link between the current cases, the CDC maintains that there is “no evidence of a contaminated water source at this time.”

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