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Around 170,574 adults admitted to public hospitals in Australia are estimated to contract hospital-associated infections (HAIs) each year, leading to 7583 deaths. This is according to by Monash University published in Antimicrobial Resistance & Infection Control.

Despite efforts to prevent and reduce HAIs, they remain an ever-present threat to patient safety. Now researchers from the have found evidence pointing to an unexpected source of such bacteria: the hospitalised patients themselves.

Studying mice, the researchers 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 (A. 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 infections.

鈥淵ou could sterilise the whole hospital, and you would still have new strains of A. baumannii popping up,鈥� said co-senior author , PhD, a professor of molecular microbiology, in a statement.

鈥淐leaning 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.鈥�

A. baumannii is a major threat to hospitalised people, 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 bacteria are said to be notoriously resistant to a broad range of antibiotics, so such infections are challenging to treat and easily can turn deadly.

Feldman teamed up with co-senior author , PhD, the Helen L. Stoever Professor of Molecular Microbiology and an expert on UTIs, 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 (E. 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.

Feldman and Hultgren 鈥� along with co-first authors Jennie E. Hazen, a graduate student, and , PhD, an instructor in molecular microbiology 鈥� 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鈥檚 urine for two months, the researchers inserted catheters into the mice鈥檚 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.

鈥淭he bacteria must have been there all along, hiding inside bladder cells until the catheter was introduced,鈥� Hultgren said in a statement.

鈥淐atheterisation induces inflammation, and inflammation causes the reservoir to activate, and the infection blooms.鈥�

Since A. baumannii rarely causes symptoms in otherwise healthy people, many people who carry the bacteria may never know they鈥檙e infected, the researchers said. As part of this study, the researchers searched the scientific literature and discovered that about 2% of healthy people carry A. baumannii in their urine.

鈥淚 wouldn鈥檛 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,鈥� Feldman said.

鈥淎s long as they鈥檙e basically healthy, it doesn鈥檛 cause any problems, but once they鈥檙e hospitalised, it鈥檚 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鈥檚 what we鈥檙e working on figuring out now.鈥�

Image credit: iStockphoto.com/Sam Edwards