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Infection Control

Quantifying The Removal Of Germs

February 01, 2011
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Given the growing public awareness of H1N1 influenza, Escherichia coli (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.

Many professionals are familiar with adenosine triphosphate (ATP) 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, a mathematical term showing a reduction in the number of live germs logarithmically, 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 a 7-log reduction.

In practical terms, a cleaning system able to provide a 5-log reduction would lower the number of microorganisms on a surface 100,000-fold.

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.

Thus, a log reduction-based cleaning system assessment 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 with a guide for determining the appropriate levels of clean and how to achieve those goals for different surfaces and environments.

Measuring microbial log reduction may help identify the processes that work best to achieve desired reductions with minimal use of chemical disinfectants within budget constraints.

Validating Processes

In August 2009, an independent laboratory certified by the U.S. Environmental Protection Agency (EPA) confirmed that a leading spray-and-vacuum 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, Clostridium difficile (C. diff), methicillin-resistant Staphylococcus aureus (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 like a commode, a urinal, a sink, a faucet handle, etc.

The floor surface was sprayed with a high-pressure fan spray for two seconds and given a two-minute dwell time before being vacuumed in a traditional manner with the system''s squeegee head.

After that, 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 two minutes.

In one scenario, the surface was dried with a blow-dry feature of the spray-and-vacuum 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 and 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 reductions in all categories.

Measurable Savings

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 achieved 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.

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-vacuum system filled with water — 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 traditional method produced a 54 percent reduction.

In both restrooms where the spray-and-vacuum 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 including setup times — manual versus machine cleaning — 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.


Tom Morrison is the vice president of marketing for Kaivac Inc., developers of the No-touch Cleaning® system. Kaivac develops science-based hygienic cleaning systems that protect the health of building occupants while raising the value of cleaning operations. For more information, visit www.kaivac.com.

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