Piping Up: Study Illuminates Bacteria’s Spread from Hospital Drainpipes

By Thomas Crocker
Saturday, July 1, 2017
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As the medical toll of multidrug-resistant bacteria rises, recent research from the University of Virginia (UVA) provides insight into how a particularly at-risk population — hospitalized patients — may contract these pathogens from a hidden nursery: a component of the piping beneath hospital sinks.

Each year, bacteria that have developed the ability to resist the antibiotics normally used to treat them cause at least 2 million illnesses and 23,000 deaths in the United States, according to the CDC. Around the globe, antibiotic resistance is increasingly hindering efforts to treat tuberculosis, malaria, HIV, urinary tract infections and gonorrhea, the World Health Organization reports.

Researchers and drug developers cannot keep pace with the development of bacterial resistance, says Amy Mathers, MD, Associate Professor of Medicine in the Division of Infectious Diseases and International Health at UVA.

“My biggest concern is antibiotic resistance developing in gram-negative bacteria because they can readily exchange genes of drug resistance and create superbugs ... with relative ease,” Dr. Mathers says. “This can happen in several environments. As there are increasing numbers of genes of drug resistance, they can be easily shared among these gram-negatives.”

A Problem of Plumbing

Individuals in hospitals and long-term-care facilities are especially susceptible to infection by multidrug-resistant bacteria, according to Tara Palmore, MD, hospital epidemiologist at the National Institutes of Health Clinical Center and Director of the Infectious Diseases Fellowship Program at the National Institute of Allergy and Infectious Diseases.

“The patients at highest risk are those who have weakened immune systems and invasive devices, such as indwelling urinary catheters and central venous catheters, as well as those who have had recent surgery or other invasive procedures that cross the body’s natural defenses,” she says.

More than 30 reports have identified a link between multidrug-resistant bacteria in hospital sink drains and other water-collection areas and infected patients, Dr. Mathers and colleagues at UVA and the University of Oxford found in a review of the literature.

“It’s not clear if there’s an increased recognition that [sink-to-patient transmission] is happening, because half of those reports were written since 2010, or if this is actually an increased problem,” Dr. Mathers says. “My suspicion is because the genes of drug resistance are becoming more consequential, the acquisition of those highly resistant bacteria is more noticeable than it was previously.”

What was also unclear was how bacteria spread from drainpipes to patients — a question Dr. Mathers and her colleagues at UVA set out to answer by creating an innovative laboratory.

Tracking Bacteria’s Spread

The UVA team built a lab of five sinks — modeled after those in the ICU at UVA Medical Center — connected by a common drainpipe system and separated the basins using 2-foot-tall Plexiglas panels. They seeded the elbow bend portions of the piping, called P traps, with a fluorescent, nonpathogenic strain of E. coli. The researchers introduced nutrients into the drain to mimic the liquids that typically enter hospital sinks, such as water, soap, beverages and bacteria from providers’ hands.

“The assumption was ... that bacteria were essentially getting carried up out of the P trap as kind of a mist,” says one of the study’s authors, William Guilford, PhD, Associate Professor of Biomedical Engineering, Director of Educational Innovation and Undergraduate Program Director at UVA. “One of our most important findings was, that appears not to happen.”

Instead, the researchers found that the bacteria climbed up the drainpipe by means of a biofilm at the rate of approximately one inch per day and reached the strainer in about a week. Once there, they could reach surrounding items and surfaces up to 30 inches away when water from the faucet splattered into the basin.

“Only when we allowed [the bacteria] to grow up the tailpiece from the standing water [in the P trap] to the top of the drain did we see dispersion to the surface of the bowl,” says Dr. Mathers, also an author of the study. “We didn’t see growth with just soap and water. We couldn’t reproduce dispersion around the sink unless we added nutrients to simulate what would be poured down the sink in a hospital environment. Even though the sinks were separated by partitions, we saw transmission along the common pipe. The bacteria grew along the common pipe and seeded the tailpiece or drainage system of the adjacent sink ... in less than a month.”

Steps to Prevent Transmission

Dr. Palmore, who was not involved in the study, says bacterial contamination of hospital sink drains is more common than many realize, although she says there is little evidence that patients obtain multidrug-resistant bacteria from them.

“Rather, the sink drains may most commonly acquire the bacteria from the patients,” she says.

Dr. Mathers says her team’s findings underscore the importance of following clinical best practices, such as hand-washing. Guilford agrees.

“Items used in patient rooms should not be on the counter surrounding the sink,” he says. “The [bacteria-containing] splatter certainly has a limited range. It’s probably not flying off into people’s beds or [going] airborne, but it’s getting onto things around the sink and then being transmitted to patients. Simply keeping the sink area clear is an enormous step forward.”