The Strain: CDC Baffled by Obscure Bug After 18 Deaths

April 7th, 2016

By Gary Evans, Senior Staff Writer

It is rare that arguably the world’s best medical detectives are frankly stumped by the cause of an outbreak that is clearly an ongoing threat to public health. This is one of those times.

The full experience and resources of the Centers for Disease Control and Prevention are being tested by an obscure bacteria called Elizabethkingia anopheles, which has arisen from an unknown source to infect at least 58 people and cause 18 deaths in two states. That is a mortality rate of 31%, though a definitive link to death is confounded by the immune deficiency and age of the patients (most >65 years).

“It does tend to be restricted to people with a weakened immune system, something like a cancer diagnosis, diabetes, liver disease -- that type of thing,” says Michael Bell, MD, deputy director of the CDC′s Division of Healthcare Quality Promotion. “We are putting a tremendous amount of effort into this because it is such a fragile population. If we can find a single source that can be either removed or contained then we can protect others in this category.”

With the exception of one case in Michigan, all of the cases have been in Wisconsin, which reported the first six cases between Dec. 29, 2015 and Jan. 4 of this year. As of April 6, state health officials in Wisconsin reported four more possible cases and one under investigation, which if confirmed would bring the total to 63 people infected. E. anopheles is a gram negative bacteria that can be naturally resistant to many antibiotics, but the outbreak strain can be treated with several other drugs so early recognition of cases is paramount. The signs and symptoms of infection include fever, shortness of breath, chills or cellulitis. Confirmation of the illness requires a laboratory test.

The CDC typically sees every state report 5 to 10 sporadic cases of E. anopheles annually, which is found in the environment, soil and water sources. What’s different about the ongoing outbreak is that all of the patients were infected by an identical strain.

“We are defining the outbreak by [genetic] sequencing and very detailed molecular typing,” Bells says.

The majority of the infections identified to date have been bloodstream infections, but some patients have had the bacteria isolated from other sites, including the respiratory tract and joints. The CDC has tested water supplies, tracked back healthcare contacts, and looked for a common source in food, medical products, over the counter personal care products, household exposures and community exposures.

“So far we have yet to show that any of those is a clear risk factor for these infections,” Bell says. "There is a possibility that we won’t find it. The challenge that we have is that the people who are likely to have known what they were exposed to in many cases are either very ill or have passed away. That can make the original source sometimes difficult to trace, but we continue to search.”

For more on this story see the May 2016 issue of Hospital Infection Control & Prevention