Hospital wastewater told a tale of antibiotic resistance, as both antibiotic use and average patient length of stay were linked to greater abundance of antibiotic resistant genes detected in molecular assays, U.K. researchers found.

Use of antimicrobials, as well as patient length of stay was reflected in the portion of antimicrobial resistant genes in the hospital wastewater -- or water affected by human use, such as that from toilets, sinks, and showers, reported Meghan R. Perry, MD, of the University of Edinburgh in Scotland, and colleagues in a manuscript published on the preprint server medRxiv.

Paul Fey, PhD, of the University of Nebraska Medical Center, told MedPage Today that the results of this study are not surprising, but they emphasize the importance of antimicrobial stewardship programs in hospitals.

"By having those programs, [there are] documented cases of decreased antibiotic resistance within organisms causing these infections," said Fey, who was not involved in the study. "This is another indicator of how all hospitals need to implement stewardship programs to have a good handle on decreasing antibiotic use."

Indeed, the topic is especially timely in this country, given the CDC's recent announcement about the success of "The AMR Challenge" -- where the U.S. has received nearly 350 commitments from 33 countries to implement country-wide programs to combat antibiotic resistance since last year.

Perry and colleagues noted the increasing interest in how hospital wastewater contributes to antimicrobial resistance.

"Sewage treatment does not completely eradicate [antimicrobial resistance] genes and thus [antimicrobial resistance] genes can enter the food chain through water and the use of sewage sludge in agriculture," they wrote. "As hospital wastewater contains inpatient bodily waste we [hypothesized] that it could be used as a representation of inpatient community carriage of [antimicrobial resistance] and as such may be a useful surveillance tool."

Researchers collected sewage over a 24-hour period from different collection points of different specialties within a tertiary care hospital in Edinburgh. They used metagenomics -- or a study of genetic material recovered from environmental samples -- to examine both hospital water samples, and samples from community sewage points.

Overall, they identified 181 clinical isolates in the wastewater sampling. The most prominent types of bacteria were Pseudomonas and Acinetobacter, though the authors noted they were mainly "environmental species" that likely represented bacteria from biofilms inside the hospital pipes, such as Pseudomonas fluorescens and Acinetobacter johnsonii. Not surprisingly, they also found a higher predominance of gut-associated bacteria in hospital samples.

In total, more than 60% of the resistome, or all the antibiotic resistance genes, in hospital wastewater and community sewage samples was comprised of the 15 most abundant genes, with most belonging to aminoglycoside and macrolide antibacterial classes, the authors said. There were 168 different resistance genes in 10 different antimicrobial classes.

Increasing use of an antimicrobial class was associated with an increase in antimicrobial resistance genes belonging to that class (IRR 2.80, 95% CI 1.2-6.5, P=0.016), albeit with a wide confidence interval, and the authors found that abundance of antimicrobial resistant genes increased with a longer patient length of stay (IRR 2.05, 95% CI 1.39-3.01, P=0.0003). However, they said that this most likely "reflects transmission among hospital patients."

Fey said that in terms of future research, it would make more sense to monitor the patients themselves rather than the hospital water, especially as sequencing technology continues to improve.

"I think that ... monitoring each patient and sequencing their bowel flora ... is more likely where we'll be able to monitor patients and see if there's significant carriage of antibiotic- resistant organisms," he said, noting that this is already being done in stewardship programs whenever a patient has a highly antibiotic resistant organism, then all patients are screened for that organism.

"In 5 years or so, sequencing [could] become so cheap that we could monitor every patient like that," Fey noted.