Obscure outbreak baffling health experts
Wisconsin experiencing outbreak of Elizabethkingia infections, bacterium never before considered a public health concern
Some 65 years ago, American microbiologist Elizabeth King peered into a microscope and discovered the “glistening, grey-white” organism that would eventually bear her name.
In the ensuing decades, the bacterium — renamed Elizabethkingia in 2005 — would fall into relative obscurity, causing only sporadic cases and the rare hospital outbreak. But late last year, something strange started happening in the state of Wisconsin.
“From the end of December to the beginning of January, we got reports from hospitals of six cases of Elizabethkingia infections,” said Karen McKeown, Wisconsin’s state health officer.
“We knew right away that it was unusual.”
That cluster was the beginning of what is now considered the United States’ largest-known outbreak of Elizabethkingia, a bacterium rarely seen in humans — and four months into their investigation, disease detectives still have no idea what could be linking these cases.
Wisconsin typically sees between two and four Elizabethkingia infections in a year but since Nov. 1, health officials have identified 59 cases, with another six suspected or under investigation. Single cases have also been confirmed in nearby Michigan and Illinois and at least 20 deaths have been linked to the outbreak.
At blame is a species called Elizabethkingia anophelis, which is particularly rare in human infections — in Canada, the public health agency is aware of just one case, reported three years ago in Quebec.
Further deepening the mystery, Illinois recently identified another 10 people who had been infected by Elizabethkingia anophelis over the last year and a half — but these cases are genetically unrelated to the Wisconsin strain.
And last week, a children’s hospital announced Wisconsin’s latest case of Elizabethkingia anophelis in an infant, though health officials are still determining whether it was caused by the outbreak strain or an unrelated one, like in Illinois. Either way, it is just the latest curveball in an outbreak that has left health officials utterly and maddeningly stumped.
“It ranks right up there (in terms of tough cases), with the mystery and the level of frustration,” said Dr. Christopher Braden, a medical epidemiologist with the U.S. Centers for Disease Control and Prevention. “There are a lot of questions that we need to answer.”
Elizabethkingia is a genus of bacteria that grows ubiquitously in the environment, with four known species. At first, investigators assumed they were dealing with Elizabethkingia meningoseptica, which has popped up in hospital outbreaks before, including a 2012 outbreak involving 30 patients at critical care unit in London, England.
But CDC investigators confirmed it was actually Elizabethkingia anophelis, a species first discovered in 2011 inside the gut of a mosquito.
Scientists still don’t know whether mosquitoes can transmit the bacterium to humans, though this was never entertained as a possibility in the Wisconsin outbreak, which started in the dead of winter.
They do know, however, that Elizabethkingia anophelis thrives in blood — and while Elizabethkingia can infect joints or the respiratory tract, most people affected by the current outbreak have suffered bloodstream infections.
“This bacterium likes animal blood cells,” Chen said. “They utilize the nutrients from blood cells and grow so quickly.”
While treatable if caught early, Eliz- abethkingia is also highly drug-resistant, he added. “More than 20 antibiotic resistance genes have been identified.”
For disease detectives, their first hypothesis was that this outbreak was hospital related.
Another hypothesis is that the outbreak could be linked by a contaminated health-care product.
However, after finding no red flags, health officials are now casting a much wider net, looking at everything from ice and skin creams to food items, with investigators tracking down restaurant receipts and hospital food invoices from patients.
Investigators may need to start “rethinking how this bug genetically behaves,” Braden said, noting that some bacterial infections, such as tuberculosis, are known to go dormant for years or even decades.
Health officials are hopeful that the outbreak is finally tapering off, but no one will be surprised to see more cases. Braden acknowledges the mystery might never be solved.
“There are outbreaks that we just don’t figure out and we know that,” Braden said. “This may be one of them.”