New research on a frightening new superbug confirms what scientists have both suspected and feared: Some hospitalized patients who carry the fungus shed large amounts of it from their skin, contaminating the environment in which they are being treated and leaving enough of it to infect others later on.
The bug, called Candida auris, is highly resistant to many existing antifungal drugs. It’s also resistant to regular cleaning methods, making hospital outbreaks incredibly difficult to stop.
C. auris acts more like bacteria than fungi, which do not normally cause hospital outbreaks. Its relatively recent emergence as a hospital-acquired infection has researchers scrambling to find out even the most basic information about it, like how it moves from patient to patient.
The new work was conducted by scientists from the Centers for Disease Control and Prevention in conjunction with colleagues from the Chicago Department of Public Health. It was presented Sunday at the annual conference of the American Society for Microbiology in San Francisco.
“As we’re struggling to control this organism, the reality is we don’t know how it’s spreading from person to person. We know that it does. But mechanistically we don’t know how. And so what this study was about was trying to identify the mechanism of how it can get from one person to the other,” said Joseph Sexton, a scientist with the CDC and the lead author of the work. “If we don’t understand how it spreads, we’re not going to be able to intervene.”
Before members of the team could conduct the study, they had to figure out a way to quantify how much of the fungus was present in any one place — a basic step in studying many pathogens, but not easy to do with C. auris, said Johanna Rhodes, an epidemiologist at Imperial College London. Rhodes, who studies C. auris, was not involved in the CDC research.
“A lot of us have been scratching our heads as to how the heck do you do this?” Rhodes said of the task of trying to devise a way to quantify amounts of the fungus. “It doesn’t have the standard set of genes that you would expect to find. It’s just such a weird bug.”
She was excited to learn of the CDC’s work — both the development of the quantification methods and the findings of the study on transmission of C. auris. Lots of people studying the fungus have assumed what the CDC team found, but it’s critical to actually have data, she said.
“We’ve all kind of said, ‘Yeah, we think this is it. We think this is what happens.’ [But] they’ve done the work,” said Rhodes. “It’s fundamental in our understanding of how this is actually spreading.”
The CDC and Chicago scientists studied 28 patients in an outbreak in what is called a ventilator-capable skilled nursing facility in Chicago. Facilities like these offer long-term care to very sick patients who are typically on ventilators, machines that breath for them. These are patients who are bed-bound.
The facility first discovered a patient carrying C. auris in March 2017. But by the time the study was done, 71% of the patients on the floor where ventilated patients are cared for were colonized with C. auris — meaning they carried it on their skin.
C. auris is an infection that is associated with patients with complex medical problems and compromised immune systems; it is generally not considered a risk to the average healthy person. But it can significantly complicate the care of people who are in intensive care units or other areas of hospitals that involve advanced care. About a third of patients who have tested positive for C. auris die, though it’s sometimes unclear if the infection was the cause of death.
The CDC-led team took skin swabs from 28 patients in the Chicago facility, swabbing their armpits and groins, which are among the places bugs that live on human bodies are often found.
They also tested a variety of surfaces in patient rooms — bed railings, doorknobs, and windowsills.
Their hypothesis was that if patient shedding was responsible for spread, they would find more of the fungus in the rooms of patients who had more of it on their skin. And indeed, they found the rooms inhabited by patients with lots of C. auris on their skin were the most contaminated with the fungus.
All of the railings on beds housing patients with C. auris tested positive for the fungus. Even the railings of two beds that contained patients who didn’t have C. auris were contaminated. Sexton said study of the patient flow on the ward revealed the beds had previously been inhabited by patients who were C. auris-positive. “So we know that they’re not doing a good enough job disinfecting the bed,” he said.
Surprisingly, three-quarters of the windowsills were also contaminated with the fungus. That was unexpected — until the team realized that windowsills were used as de facto shelves in these rooms.
“If there is a takeaway it could be …. ‘Hey, we really need to pay attention to the bed and these other areas that the patient is in contact with,’” said Sexton.