The Mölnlycke Health Care blog

Clean air in the O.R.: How to measure CFU?

By : Glenn Lundberg, October 6 2015Posted in: The Mölnlycke Health Care blog

Glenn Lundberg is a former surgery nurse who is now a clinical specialist with Mölnlycke Health Care.

There is a lot of discussion about clean air and CFU (colony forming unit) levels in operating theatres. Evidence points to the importance of reducing the number of CFUs, which are a measure of viable bacterial or fungal cells, to achieve ultra clean air and reduce the bacterial burden in the operating room1,2,3.

In practice, however, not all hospitals have the experience or know-how to implement CFU measurement across the board. Therefore, a question that comes up a lot when meeting hygiene nurses and staff is: How?

In Sweden, hygiene nurses often drive CFU measurement tests to get ultra clean air in the operating room. They start by controlling the ventilation, tracking how many persons are within the O.R., controlling the routines around hygiene and pre-cleaning, and controlling routines around clothing. They often look into routines before surgery in the ward departments, during surgery in the O.R. and after the surgery where the patient wakes up. That is, they measure the CFU level before any activity takes place and then take action and switch to clean air suits and measure again. There is a technical specification, SIS TS 39:2012, that states how to measure CFU levels, where to place the agar plates, to make sure the measurements accurately compare apples and apples (or like to like). The TS also provides instructions for the settings the equipment must have, how many measurements should be taken and how long to let the agar plate have time to grow.

Many hospitals have air samplers to perform tests of CFU levels within the O.R. as these hospitals already measure the CFU in their labs, pharmacies, clean rooms or sterile centres regularly, meaning that the knowhow is already embedded within these organizations.

One hospital noticed that they had many surgical site infections in their orthopaedic department. They took measurements and saw that they had high CFU levels. Knowing the importance of ultra clean air, they asked for advice. I asked them when they last had a technician inspecting and cleaning their ventilation system and recommended that they start wearing single-use clean air suits when performing implant surgeries. They took these actions and saw both their CFU levels and SSI numbers decrease.

My recommendation is to measure your CFU levels in the O.R. regularly to secure the best possible outcome for your patients. If you find you have to high CFU levels within your O.R. you need to take action. It may be that you need to implement new procedures. Evidence shows that there are several factors determining what your CFU levels are1,4,5. Among these are ventilation, the number of door openings during procedure, number of people in the O.R. and staff clothing6,7,8.

Other studies show that it may be enough to change your staff clothing to reach the desired levels of less than 10 CFU/m3. Ultra clean air.

Do you know what the CFU levels are in your O.R.?



  1. Lidwell OM, et al. Ultra-clean air and antibiotics for prevention of postoperative infection: a multi-center study of 8,052 joint replacement operations. Acta Orthop Scand, 1987; 58(1): 4-13.
  2. Hoborn J. Thesis: Humans as Dispersers of Microorganisms - Dispersion Pattern and Prevention. Department of Clinical Bacteriology, Institute of Medical Microbiology, University of Göteborg, Göteborg, Sweden. 1981.
  3. Swedish Technical Specification SIS-TS 39:2012. Microbiological cleanliness in the operating room – Preventing airborne contamination – Guidance and fundamental requirements.
  4. Lidwell OM, et al. Effect of ultraclean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomised study. BMJ1982;285:10-14.
  5. Lidwell OM, Lowbury EJL, Whyte W. Airborne contamination of wounds in joint replacement operations: the relationship to sepsis rates. J Hosp Infect 1983;4:111-31.
  6. Lippert S, Gutschik E. Bacterial sedimentation during cardiac surgery reduced by disposable clothing. Scand J Thorac Cardiovasc Surg 1992; 26: 79-82.
  7. Blomgren G, Hoborn J, Nyström B. Reduction of contamination at total hip replacement by special working clothes. J Bone Joint Surg [Br] 1990;72-B:985-987.
  8. Tammelin A, et al. Single-use surgical clothing system for reduction of airborne bacteria in the operating room. Journal of Hospital Infection, 2013.
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The surgical and wound care environment is always changing. The Mölnlycke Health Care blog addresses topics and trends in surgery and wound care. Among these topics are efficiency, health economy, infection control and patient safety. Read more about this blog and how to comment.

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