Log Reduction: Quantifying the Removal of Germs Under ICM Using Less Toxic or Greener Methods
Given the growing public awareness of H1N1, E. coli and other 'invisible' contaminants, service providers striving to clean for a healthier environment should be able to control or remove these threats and prove it. How?
Many professionals are familiar with ATP or adenosine triphosphate measurement as a means to measure the removal of organic soil – alive or dead.
However, when it comes to determining actual germ kill, 'inactivation' or removal, log reduction is important to understand.
Log reduction is a mathematical term showing a reduction in the number of live germs logarithmically. It denotes the relative number of live microbes eliminated from a surface because of sanitizing, disinfecting or cleaning. A '1' log reduction means the number of germs on a surface is 10 times smaller than prior to cleaning. A '2' log reduction means the number is 100 times smaller, a '3' log reduction is 1,000 times smaller and so on up to '7' (10,000,000 times smaller).
In practical terms, a cleaning system – the techniques, equipment and cleaning solutions – able to provide a '5' log reduction would lower the number of microorganisms on a surface 100,000-fold, i.e. after the system is employed, a surface with 100,000 microbes on it prior to cleaning would be left with 1.
Log reduction also should embrace the concept of Soil Removal Over Time (SROT) in the Integrated Cleaning and Measurement (ICM) approach; that is, to be practical, log reduction must be coupled with how long it takes for this to occur.
A log reduction-based cleaning system assessment thus should provide measurable, time-factored levels of germ-reduction for objectively evaluating and comparing different systems and methodologies.
This same approach can also help provide cleaning service providers a guide for determining the 'appropriate' levels of clean and how to achieve those goals for different surfaces and environments. Professionals, for both pragmatic and public health reasons, should neither be doing too little cleaning or sanitizing or doing too much, especially when it involves harsh chemistries.
Excessive use of aggressive chemicals and other cleaning solutions in areas that may not require such treatments to achieve a satisfactory level of clean may create serious health problems and also result in excessive costs.
Measuring microbial log reduction may help identify the processes that work best to achieve desired reductions with minimal use of chemical disinfectants and within budget constraints.
Water-Only Spray-and-Vac Cleaning Validated
In August 2009, an independent, U.S. Environmental Protection Agency-certified laboratory in Muncie, Ind. confirmed that a leading spray-and-vac system qualified as a sanitizing device under EPA rules when tested using plain water and no chemicals. Results showed that the system, when used as directed, achieves a greater-than 99.9 percent reduction of E. coli, C. difficile, MRSA, pseudomonas and salmonella bacteria in a very short time period.
The tests were designed to assess cleaning restroom floors as well as above floors. To recreate these conditions in a laboratory, materials were selected to simulate tile and other smooth surfaces. Two sets of tests were performed, to represent cleaning the floor as well as above-floor fixtures, e.g. commode, urinal, sink, faucet handle, etc.
The ‘floor surface' was sprayed with a high-pressure fan spray for 2 seconds and given a 2-minute dwell time. It was then vacuumed in a traditional manner with the system's squeegee head. Microbe levels were measured to see how many colony forming units (CFUs) survived.
In the second series of tests, vertical surfaces were sprayed with the high-pressure fan spray, and allowed to dwell for 2 minutes. In one scenario, the surface was dried with a blow-dry feature of the spray-and-vac system; in another it was allowed to dry on its own. This represented different cleaning situations: fixtures cleaned in locations that might be used almost immediately, such as airport restrooms, may need blow drying; whereas in a school restroom cleaned after hours these surfaces might be allowed to air dry.
Each test was performed multiple times with five different bio-contaminants to confirm results. Bacteria concentrations were measured before and after treatment by the system. Based on the before and after measurements, log reduction was determined.
For an EPA sanitizing device claim to be made, a system needs to be able to show at least a 3-log reduction of the bacteria; tests showed the system achieved between 4-log and 6-log reduction in all categories.
Measurable Labor Savings
Something else emerged. Instead of following the traditional methodology of putting down chemical with a low-pressure fan spray, letting it dwell, then returning and rinsing with a high-pressure fan spray; one-pass, water-only cleaning delivered in a high-pressure fan spray not only delivered the desired cleaning results, it cut 30 percent to 50 percent off the time required to clean and greatly reduced the amount of water needed.
Cleaning without Chemicals to Effectively Remove Organic Matter
Separately, recent tests conducted at the University of Washington also found that cleaning without chemicals to remove organic soil may be as good as or better than cleaning with those products.
Two identical sets of restrooms in the university's Health Sciences Building, one male and one female, were selected. An experienced worker used properly diluted EPA-registered products to clean and wipe down faucets, sinks and counters in one set of restrooms. Toilets were disinfected, and the floors were cleaned using a microfiber wet mop and properly diluted and applied EPA-registered products.
In the other set of restrooms, a worker used a spray-and-vac system filled with water, but no chemicals. Vertical and horizontal surfaces were spray-washed, fixtures were wiped down, countertops were squeegeed and the floor was vacuumed.
Before and after both sets of restrooms were cleaned, swab samples were taken in the same locations – sink countertops, floor tile a yard from the entrance in the main walkway and floor tile two feet in front of the toilet in the first stall – and placed in an ATP measuring device.
Results demonstrated that spraying, agitating and vacuuming surfaces produced an average 89 percent reduction in ATP, while the microfiber/traditional method produced a 54 percent reduction; that is, the spray-and-vac system, using only water, produced 58 percent better results. In both restrooms where the machine was used, ATP levels dropped below 30, which is considered sanitary; in two of the test sites, the count actually dropped to zero. Labor times for both processes - manual versus machine cleaning, and factoring in setup time - were similar.
Based on the foregoing, combining microbial log reduction assessment with other recognized measurement protocols such as ATP can identify better processes that can help professionals achieve healthier environments with greater efficacy and lower costs – without unnecessary or excess use of antimicrobial chemistries.
Determining the actual time-based log reduction of germs in any cleaning process thus should be a strong component in any progressive Integrated Cleaning and Measurement (ICM) program.
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