Despite stringent infection-control efforts around the world, hospital-acquired infections (HAIs)keep on popping up from new strains of bacteria. In Science Translational Medicine, researchers report evidence pointing to an unexpected source of such bacteria: the hospitalised patients themselves.
From experiments with mice, researchers at Washington University School of Medicine in St. Louis discovered that urinary tract infections (UTIs) can arise after sterile tubes, called catheters, are inserted into the urinary tract, even when no bacteria are detectable in the bladder beforehand. Such tubes are commonly used in hospitals to empty the bladders of people undergoing surgery. In the mice, inserting the tubes activated dormant Acinetobacter baumannii bacteria hidden in bladder cells, triggering them to emerge, multiply and cause UTIs, the researchers said.
The findings suggest that screening patients for hidden reservoirs of dangerous bacteria could supplement infection-control efforts and help prevent deadly HAIs.
“You could sterilise the whole hospital, and you would still have new strains of A. baumannii popping up,” said co-senior author Mario Feldman, PhD, a professor of molecular microbiology. “Cleaning is just not enough, and nobody really knows why. This study shows that patients may be unwittingly carrying the bacteria into the hospital themselves, and that has implications for infection control. If someone has a planned surgery and is going to be catheterised, we could try to determine whether the patient is carrying the bacteria and cure that person of it before the surgery. Ideally, that would reduce the chances of developing one of these life-threatening infections.”
The notoriously multidrug-resistant A. baumannii is a major threat to patients, causing many cases of UTIs in people with urinary catheters, pneumonia in people on ventilators, and bloodstream infections in people with central-line catheters into their veins.
The researchers set out to investigate why so many A. baumannii UTIs develop after people receive catheters.
Most UTIs among otherwise healthy people are caused by the bacterium Escherichia coli. Research has shown that E. coli can hide out in bladder cells for months after a UTI seems to have been cured, and then re-emerge to cause another infection.
The researchers investigated whether A. baumannii can hide inside cells like E. coli can. They studied mice with UTIs caused by A. baumannii. They used mice with weakened immune systems because, like people, healthy mice can fight off A. baumannii.
Once the infections had resolved and no bacteria were detected in the mice’s urine for two months, the researchers inserted catheters into the mice’s urinary tracts with a sterile technique. Within 24 hours, about half of the mice developed UTIs caused by the same strain of A. baumannii as the initial infection.
“The bacteria must have been there all along, hiding inside bladder cells until the catheter was introduced,” said co-senior author Scott J. Hultgren, PhD, a professor and expert on UTIs. “Catheterisation induces inflammation, and inflammation causes the reservoir to activate, and the infection blooms.”
Since A. baumannii rarely causes symptoms in otherwise healthy people, many people who carry the bacteria may never know they’re infected, the researchers said. According to the researchers’ literature search, 2% of healthy people carry A. baumannii in their urine.
“I wouldn’t put much weight on the precise percentage, but I think we can say with certainty that some percentage of the population is walking around with A. baumannii,” Feldman said. “As long as they’re basically healthy, it doesn’t cause any problems, but once they’re hospitalised, it’s a different matter. This changes how we think about infection control. We can start considering how to check if patients already have Acinetobacter before they receive certain types of treatment; how we can get rid of it; and if other bacteria that cause deadly outbreaks in hospitals, such as Klebsiella, hide in the body in the same way. That’s what we’re working on figuring out now.”
