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 at the CDC 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. The CDC issued a nationwide call for cases on January 20, 2016, via the Emerging Infections Network and again on March 2 through the Epidemic Information Exchange system. The alerts asked states to look for any infections similar to the ones reported in Wisconsin, and to send isolates from any potential cases to CDC for testing to determine if they match the bacteria causing infections in the Wisconsin. The only isolate that has matched the Wisconsin outbreak is the single case in western Michigan.
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, Bell says. What is 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,” he says.
Most cases have BSIs
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. With a hospital outbreak1 of another variety of the bacteria (E. meningoseptica) reported earlier this year, a history of healthcare contact was an immediate source of suspicion.
“So far, that is not showing up as being a common link,” Bells says. “Not everyone has had healthcare exposures. Some have, but then the age of many of the individuals affected makes it likely that they are going to have contact with healthcare. A couple of them have lived in long-term care facilities and others have been in hospitals, but several have not. It doesn’t present itself as a rational common source.”
The aforementioned nosocomial outbreak was traced to tap water and sinks in a critical care unit, so water sources were tested very early in the ongoing community outbreak.
“We wanted to make sure that it wasn’t something like a municipal water system,” he says. “None of the testing we have done so far shows any relationship with a shared water source like that.”
In addition to water supplies and healthcare contacts, the CDC has looked for a common source for the outbreak in food, medical products, over-the-counter personal care products, and both household 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.”
REFERENCE
- Moore L, Owens DS, Jepson A, et al. Waterborne Elizabethkingia meningoseptica in Adult Critical Care. Emerg Infect Dis 2016;Jan: http://bit.ly/1XldK4s.
