In our recent blog postings, we have examined some of the growing levels of evidence for contamination (both bacterial and fungal) of high touch surfaces in the environment. In addition those high touch surfaces are the same surfaces that are not only contaminated but also interacted with by healthcare workers and other personnel during the course of their day.

In order to describe and review the levels of hospital contamination, and what standards exist for control of those levels on both soft and hard surfaces we need to briefly review how we measure those levels. There are two main systems for measuring hospital contamination.

  • ATP measurement

Adenosine Tri Phosphate (ATP) is a key molecule in living cells. ATP helps carry energy between cellular reactions and is biosynthesized by cells. As  it is ubiquitous in living cells, and by harnessing the reaction of ATP with luciferase (a firefly enzyme) in a two step reaction we can quantify microbial cell counts. As the reactions of ATP with luciferase produce light we can then measure and record the light emitted, and therefore cell counts can be quantified. ATP and Luciferase undergo a first step to produce luciferyl adenylate and pyrophosphate. The second step utilizing luciferyl adenylate and oxygen produces oxyluceriferin, AMP and light. This light can be detected using a luminometer.  ATP test strips and luminometers can then be used on any surface to generate Relative Light Units or RLU which is the measure of ATP generated into light.

  • Environmental sampling and count data

The traditional method of enumeration of contamination in the environment is via sampling of that environment and counting colonies or alive cells on agar petri dishes. This can be conducted by using a standard size template (typically 10cm X 10cm) sampled in every direction using a swab (dacron/cotton tipped, a sponge, a pre moistened swab, or a swab with a variety of transport media).  The sampling methodology is well outlined here. Alternate options include push plates or Replicate Organism Detection and Counting (RODAC) plates.

RODAC plate
RODAC plate

RODAC plates are petri dishes filled with agar to a convex surface. This surface is directly pressed onto the surface, labelled and incubated. Count data can then be generated directly from the contact plates after incubation. Contact plates are often offered with a range of  neutralizer agents contained within them in order to neutralize the impact of cleaning agents and serve as an excellent pre/post monitoring system for the effectiveness of disinfection and cleaning.

Typically ATP measurements or environmental swabbing and counts should be routinely used as an assessment tool for efficacy of cleaning/hygienically disinfecting the surfaces. This tool should be used in conjunction with cleaning schedules should be adapted to reflect clinical risk, location, type of site, and hand touch frequency and should be evaluated for cost versus benefit for both routine and outbreak situations (1).

At this point it is important to make the distinction between “clean” and “hygienic or disinfected”. Clean or cleaning refers to improvement of the aesthetics of a surface or removal of organic material from a surface in order to functionally improve the use and interaction with that surface, whilst hygienic or disinfected refers to the removal of microbial contamination to protect the user from pathogenic microorganisms. This is an important distinction,  as currently there are only visual standards for cleanliness in hospitals, and patient/visitor feedback is frequently requested as a measure of care-“How clean was your room”?.  The standards that exist for hygienic surfaces or disinfected surfaces are also wide and varied and firstly we will look at standards based around environmental swabbing and colony counts.

Currently a range of microbiological sampling and counts standards exist for environmental soft surfaces based upon a range of accreditation agencies. These limits exist as 20cfu/dm2 for healthcare laundries and institutional laundries that serve medical facilities, to 50cfu/dm2 for laundries that service the food industry.  This rises for moist textiles to 30cfu/dmfor the healthcare servicing laundries and 100cfu/dm2 for laundries that service the food industry. In all cases no human pathogens should be isolated on the textiles.

For the hard surfaces in the patient room the only standard as mentioned earlier is the cleanliness of the room which is addressed via a visual inspection. S. J. Dancer has proposed microbiological standards  (2) for surface hygiene in hospitals. The proposal by Dr Dancer is to use a quantitative colony count that is based upon the food industry to define general aerobic microbiological limits on  surfaces. In addition Dr Dancer proposes a quantitative limit of indicator organisms (human pathogens) on the surfaces also. Dr Dancer proposes that <1cfu/cm2 of indicator species-S. aureus, MRSA, C. difficile, MDR Gram-negative bacilli, VRE, Salmonella and any organisms associated with outbreaks of infection incidences (e.g Aspergillus in units that house immunocompromised patients). Further the standard for the total aerobic colony count a measure of all aerobic organisms sampled in an area should be <5cfu/cm2. 

In the ATP sampling regimes a range of standards have been proposed, but again no adopted standards are available for this microbial load assessment tool. Suggested levels of Relative Light Units (RLU) of 500 RLU (3) was initially proposed, which was then updated to 250 RLU (4) , and further modified to 100 RLU (5) have all been proposed in the literature as pass/fail criteria for surfaces.

What we can say for certain are that current standards are based around visible cleanliness of surfaces, which by removing organic soil has been known for over 50 years to physically reduce bioburden (6). However it has been recently demonstrated (7) that visible assessments of cleanliness is  a poor indicator of cleaning efficacy and microbial surface counts. Further without the adoption of ATP RLU standards or microbiological count data standards as proposed by other authors, these tools are best served for purely assessing the efficacy of a cleaning regime in order to identify areas requiring greater intervention to reduce microbial counts, as part of a broader cleaning audit and internal testing service. The tools suggested for monitoring cleaning also highlight that the RLU units or count data for presence of pathogenic indicator species or general buioburden is only post cleaning and these levels can only be maintained via the use of surfaces designed to continually reduce microbial contamination.

All of us at Cupron would like to wish you and your family a happy holiday period, and in celebration of the festive period I leave you some festive art made from fungal strains from the J. Craig Venter Institute blog
Fungal Christmas tree. Top: Talaromyces stipitatus; Tree: Aspergillus nidulans; Ornaments: Penicillium marneffei; Trunk: Aspergillus terreus. Fungal Christmas tree. Top: Talaromyces stipitatus; Tree: Aspergillus nidulans; Ornaments: Penicillium marneffei; Trunk: Aspergillus terreus.

Fungal snowman. Hat, Eyes, Mouth, Buttons: Aspergillus niger; Arms: Aspergillus nidulans; Nose: Aspergillus terreus with Penicillium marneffei; Body: Neosartorya fischeri.
Fungal Christmas Tree
















References cited in this article

1.Dancer SJ. Controlling hospital-acquired infection: focus on the role of the environment and new technologies for decontamination. Clin Microbiol Rev. 2014 Oct;27(4):665-90

2.Dancer SJ. How do we assess hospital cleaning? A proposal for microbiological standards for surface hygiene in hospitals. J Hosp Infect. 2004 Jan;56(1):10-5

3. Griffith, C.J. et al, 2000. An Evaluation of hospital cleaning regimes and standards. Journal of Hospital Infection. 45:19–28.

4. Lewis, T. et al., 2008. A modified ATP benchmark for evaluating the cleaning of some hospital environmental surfaces. Journal of Hospital Infection. 69:156–168.

5. Mulvey D, Redding P, Robertson C, Woodall C, Kingsmore P, Bedwell D, Dancer SJ. Finding a benchmark for monitoring hospital cleanliness. J Hosp Infect. 2011 Jan;77(1):25-30


7. Malik RE, Cooper RA, Griffith CJ. Use of audit tools to evaluate the efficacy of cleaning systems in hospitals. Am J Infect Control. 2003 May;31(3):181-7.


You Tube video courtesy of TSCswabs

Festive art from J. Craig Venter Institute blog