How do you solve a problem like the sink drain? So goes the line in possibly the Sound of Music’s most well-known song. Well, perhaps not, but there’s no denying that sinks and drains and the nasty microorganisms that inhabit them are a growing problem in healthcare. 

For a number of years now, researchers all over the world have been investigating sinks and drains as a potential source of hospital-acquired infection (HAI)-causing microorganisms, especially carbapenem-resistant Enterobacteriaceae (CRE). CRE infections are of particular concern because of their ability to transfer their resistance genes from one bacterial species to another, say from carbapenem- resistant Klebsiella pneumoniae to Escherichia coli, and they’re difficulty to treat.

In 2000, a paper in Current Opinions in Microbiology posed the question “Is the emergence of carbapenemase a problem waiting to happen?” Almost 20 years on, the problem is here. Reports that suspected sinks and drains could be the source of CRE that caused HAIs began to emerge in 2003. In 2017 a review, The Hospital Water Environment as a Reservoir for CRE Causing Hospital-Acquired Infections, included 17 reports that identified sinks as a potential source of microorganisms, including CRE, that caused HAI outbreaks, often in the ICU. 

More reports have appeared in the literature since then. Recently, two investigations of outbreaks in ICU in China and Israel employed molecular methods to confirm that ICU sinks were indeed the cause of CRE infection outbreaks. 

So how does CRE get from the drains to patients?

Some excellent work from the United States has increased our understanding of this.  It turns out that bacteria can spread along common pipes connecting sinks and colonize the p-trap. Once there, they form a biofilm which can grow upwards to reach the sink strainer at a rate of up to an inch a day if fed with nutrients such as juice or coffee. Then, as the U.S. study and one from the United Kingdom show, water from the faucet directly hitting the sink strainer can splash on to surrounding counters and the floor up to three feet away from the sink, bringing with it the bacteria that have contaminated the sink strainer. If splashing does occur, patient care items left around the sink can become contaminated, increasing the chance of transmission of pathogens to patients. It’s the CRE and other pathogens isolated from sink drains and transmitted via this splashing that are suspected as the source of hospital-acquired infections.    

What have hospitals done to tackle sinks as a source of CRE?

Not surprisingly, hospitals have tried a range of interventions to stop outbreaks, with varying degrees of success, and the 2017 review covers these. They include:

  • Replacing the entire contaminated sink units or replacing the downpipes and p-traps (both costly)
  • Regularly pouring disinfectants down the sink
  • Using a device that heats and subjects the downpipe to ultrasound to kill and remove the biofilm. 

Some interventions resulted in the end of the outbreak but didn’t fully eliminate CRE from the environment and the potential of a CRE infection occurring. Others were not successful at eliminating the outbreak at all. 

What interventions are being researched?

Pouring disinfectants such as bleach, hydrogen peroxide and acetic down sink drains significantly decreases bioburden but regrowth happens within a few days. Blocking the drain and allowing the disinfectant to sit in the p-trap and downpipe is more successful, with regrowth taking longer. A simple device that covers the sink strainer and held in place with three suction cups is able to successfully prevent water from the faucet hitting the sink strainer and then splashing on to sink surrounds. A much more complex intervention consisting of a sink bowl that limits water dispersion and a mechanism that enables the faucet to dispense disinfecting ozonized water is effective at decreasing Pseudomonas aeruginosa and Candida auris contamination but is clearly a more costly intervention. Research in this area is likely to continue.   

What does CDC suggest?

The Centers for Disease Control and Prevention’s (CDC) guidance document, Reduce Risk from Water: From Plumbing to Patients, includes a section on how to reduce the risks of transmission of MDROs from sinks, drains and plumbing. Many recommendations have their origins in the reports in the literature and include:

  • Regularly cleaning and disinfecting surfaces near drains and around sinks
  • Avoiding placing patient care items on counters next to sinks
  • Not placing sinks next to medication preparation areas or separating them with splash barriers
  • Preventing faucets from discharging directly above sink strainers, ensuring that water flows are in line with FGI Guidelines
  • Installing sinks that reduce the possibility of splashing
  • Not discarding patient waste or sources of nutrients such as beverages down sinks 

The CDC guidelines stop short of recommending pouring disinfectants down sinks on a regular basis, most likely because no one antimicrobial ingredient has been found to be better than others, and ideal concentrations to use are not known. 

It seems clear then that there’s no silver bullet that will completely eliminate the risk of pathogen, and particularly CRE transmission from sinks. Instead, like with many infection prevention solutions, a bundle of small interventions — behavioral, such as better housekeeping around sinks; practical, such as regular cleaning and disinfection; or design-related, such as replacing sinks or putting diverting water from the faucets — will likely be required to solve a problem like the sink drain.