What’s lurking in your Hospital sink drain?


Have you ever wondered what is in a sink drain, the photo below was taken from a Hospital sink U-bend.

Figure 1: Looking down into drain U-bend from a sink

The debris in a sink drain is a ripe biofilm full of many types of bacteria some of which are pathogenic. This is a problem because drains “breathe” or “pant” as the air changes pressure on the other side of the U-Bend. This leads to air being pushed out of the sink laden with bacteria back into the air surrounding the sink.

If you have a vulnerable patient in the vicinity this leads to a risk to the patient.

As an example a study carried out by Moloney et al, published in the Journal of Hospital Infection (https://doi.org/10.1016/j.jhin.2019.11.005), found that twenty five washbasin U-bends contained Pseudomonas aeruginosa but that the taps and water from the same sinks were clear.

This raises an interesting point that many biocides claim to kill bacteria such as Pseudomonas aeruginosa and this is undoubtedly true however this is when the bacteria are in the water phase. In the upper reaches of the sink drain there is no water so a liquid biocide claiming to remove bacteria will not be effective if not in contact with the biofilms.

What is required therefore is a biocide that can be made to be in contact with the bacteria for a significant amount of time. This can be achieved by using a biocide held in a Rheopectic foam that will significantly increase the contact time between the foam containing the biofilm and the drain surfaces. However, the process to achieve this is key so that the bacteria from the drain are not reintroduced to the environment in the sink itself.

Figure 2: Example of the properties of a rheopectic foam when squirted through a shower hose.

Whilst it is possible that the Pseudomonas aeruginosa came from hand washing, which would explain why when the water was clear the sink drain was not, another study produced interesting findings.

The study by Grabowski et al, published in the Journal of Hospital infection (https://doi.org/10.1016/j.jhin.2018.04.025), found that of 4810 sink usages only 4% related to hand hygiene and 56 of the activities were where a variety of nutrients, which could promote microbial growth, were disposed of in the sink. The conclusions were of interest as sinks were used as storage facilities, waste disposal outlets and other non-hygiene related activities. Further in one study making an ICU room waterless led to a reduction in the transmission of drug-resistant gram-negative bacteria. This shows that misuse of sinks has an important part to play in keeping sinks free from Pseudomonas bacteria.

Another study, by Aranega-Bou et al (https://doi.org/10.1016/j.jhin.2018.12.007) found that bacterial dispersal from rear draining sinks was almost 30 times less than from sinks with the drain underneath the tap. The design of the sink and the drain location is a key factor in dispersal of bacteria into the patient area.

In Germany a study found that plastic materials and stainless steels increased the likelihood of biofilms compared to copper so the choice of drainage materials of construction can also be important.

There are some important lessons to be learnt here:

  • Pathogenic bacteria can be introduced to the drains by handwashing but as handwashing appears to be the least frequent use of a sink it is by the misuse of a sink that promotes bacterial contamination
  • Sinks “breathe” and so can push pathogenic bacteria into the patient environment.
  • Use of liquid biocides is likely to have limited effect on controlling biofilms in the upper reaches of the drain as there is no water present and so a rheopectic foam containing a biocide seems more appropriate.
  • The process for cleaning the sink will then become more important to ensure no contamination is transferred from the drain to the sink.
  • The design of the sink and materials of construction can affect the likelihood of bacterial growth and contamination of the patient environment.

If you need more information on how to ensure your patient environment is protect then contact Collaton Consultancy.