Hospital Wastewater Teems with Antibiotic-resistant Organisms

NIH study finds effective surveillance efforts for drug-resistant organisms minimize patient infections, even close to a reservoir of resistant bacteria.

Hospitals do a good job killing antibiotic-resistant organisms in high-touch areas such as counter tops, doorknobs, computer keyboards, and sinks, a new National Institutes of Health study says.

However, drainage pipes under hospital intensive care units, and in outside sewers that collect hospital wastewater are teeming with those organisms, including bacterial plasmids that confer resistance to carbapenems, the "last-resort" antibiotics given to hospital patients who develop infections from pathogens that are multidrug-resistant, the researchers report in mBio.

"Strikingly, despite a very low prevalence of patient infections with bla_KPC-positive organisms, all samples from the intensive care unit pipe wastewater and external manholes contained carbapenemase-producing organisms, suggesting a vast, resilient reservoir," the study said.

That comparison suggests that surveillance efforts to watch for resistant organisms minimize patient infections, even so close to a reservoir of resistant bacteria, says NIH microbiologist Karen Frank, who co-led the study.

"If you're tracking resistant bacteria, you might be able to prevent more infections in patients," she says.

The study also raises an important question.

"How much should we care that there are a bunch of plasmids down in the wastewater system if they're not infecting our patients?" Frank says.

The new findings add to growing evidence suggesting that the conduits of hospital wastewater serve as a vast, resilient reservoir for plasmids that can confer the genes responsible for antibiotic resistance.

Frank says these populations flourish in wastewater because of the common use of strong antibiotics in hospitals, which leads to an uptick in antibiotic-resistant microbes in the sewers.

"The bacteria fight with each other and plasmids can carry genes that help them survive," she says.

As part of a complex bacterial community, they can transfer the plasmids carrying resistance genes to each other, which means that the bacteria can gain resistance without exposure to antibiotics.

NIH researchers compared their data to five years' worth of patient data and samples collected from sinks and other high-touch areas, like countertops, door knobs, and computers. Remarkably, the high prevalence of carbapenem-resistant plasmids in the pipes and sewers wasn't seen in parts of the hospital to which patients had access. Of 217 samples analyzed from high-touch surfaces, only three (1.4%) tested positive for carbapenem-resistant organisms. Similarly, of 340 samples collected from drains, only 11 (3.2%) were positive.

Frank says understanding the plasmid exchange and when the plasmids get into the pathogens that infect our patients could help hospitals improve their monitoring of resistance-conferring genes.

"In the big picture, the concern is the spread of these resistant organisms worldwide and some regions of the world are not tracking the spread of the hospital isolates," she says.