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Infection Control

When Disinfectants Fail: How Newer Technologies Can Help

April 25, 2012
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Traditional disinfectants have undoubtedly prevented a great number of infections over the years.

Regrettably, though, many outbreaks are still spread by contaminated surfaces, and the technical drawbacks of liquid disinfectants may be partially to blame for high facility-acquired infection rates in health care.

Fortunately, new surface decontamination technologies are emerging to supplement — and even replace, in some instances — traditional disinfectants.

Chemical disinfectants registered by the U.S. Environmental Protection Agency (EPA) kill microorganisms reliably in laboratory tests; there is no question about that.

However, disinfectants routinely fail in practice.

French et. al.showed that conventional disinfection failed to reduce the presence of methicillin-resistant Staphylococcus aureus (MRSA) on 66 percent of tested surfaces and Byers et al. found that conventional disinfection failed to reduce vancomycin-resistant enterococci (VRE) contamination in 15.9 percent of sampled sites.

Most recently, Stibich et al. reported 33 bacteria per square centimeter "before cleaning" in rooms of a cancer center and a reduction to 27.4 bacteria per square centimeter after traditional terminal room cleaning and disinfection.

That corresponds to a reduction in bacteria on environmental surfaces of just 17 percent.

The main reasons disinfectants fail in practice are described below:

  • Product not applied liberally for the right amount of time
  • Wrong active ingredient in use for the microorganism(s) of concern
  • Contaminated surfaces are missed by cleaning staff.
Dwelling On Contact Times

The number one reason disinfectants fail in practice is that too little volume is applied to target surfaces, and liquid that is applied is not left there long enough to do its job.

Every EPA-registered disinfectant product label lists detailed application instructions.

Generally, these specify a pre-cleaning step followed by liberal application of the disinfectant, then a "dwell" or contact time.

For example, one well-known disinfectant''s label directs users to, "Spray surface until thoroughly wet. Let stand 10 minutes."

Such language is not merely a recommendation; use instructions cascade directly from parameters used in laboratory testing.

For spray products, microorganisms inoculated onto a glass slide in a Petri dish are sprayed three to five times and then allowed to sit for 10 minutes prior to evaluation of disinfection.

In laboratory testing, the ratio of liquid to surface area is enormous; if one wanted to use this same ratio to clean the high-touch surfaces in a single hospital room — to get true disinfection — about a gallon of product would be needed.

The volume of product required to get true disinfection from liquid chemicals on a surface is simply not realistic in many cases.

One can still achieve sufficient sanitization, however, so long as an appreciable volume of product is applied for the full contact time on the label.

A reasonable and effective application of disinfectant product may be one full spray of disinfectant per square foot of surface area.

Applying disinfectant products for the full contact time on the label is clearly very problematic.

The reality is that hospital staff may only spend 10 minutes cleaning a room, so adhering to label-stated contact times is not practical in this context.

Furthermore, disinfectant will run off vertical and other irregular surfaces during the proposed contact time and may simply evaporate before the proper dwell time is reached.

A study conducted by Antimicrobial Test Laboratories LLC demonstrated what happens to the efficacy of a disinfectant chemical when used in a manner close to what is commonly observed in the field.

The results of this controlled laboratory study showed that for ultra-low contact times, traditional disinfectants left many microorganisms behind on the surface.

A Simmering Solution

Steam vapor for surface disinfection is a newer technology that disinfects more quickly than chemicals and helps address many of the issues that plague disinfectants in normal use.

Commercial steam vapor systems produce a targeted amount of "saturated" steam with relatively low moisture content, high temperature and low particle size relative to steam produced by ordinary steam cleaners.

Additionally, commercial steam vapor systems greatly reduce the potential for surface-to-surface or room-to-room cross-contamination because the cleaning tool remains very hot.

This is in contrast to traditional approaches, which may actually spread pathogens from one surface to the next if the disinfectant becomes overused or is inactivated.

Another reason disinfectants sometimes fail in the field is that some lack efficacy against problematic microorganisms.

Most EPA-registered chemical disinfectants are efficacious against "typical" gram-negative and gram-positive bacteria, such as Escherichia coli (E. coli) and Staph.

However, a great many EPA-registered products lack efficacy against certain viruses, including norovirus, and bacterial endospores.

As such, it is important to recognize these deficiencies to prevent normal disinfection activities from making contamination problems worse by spreading problematic microorganisms around the facility.

A traditional approach to expanding the breadth of kill spectrum is to rotate bleach into the disinfection regimen.

Bleach is a well-known broad-spectrum disinfectant that is effective against virtually all microorganisms, including norovirus and Clostridium difficile (C. diff).

However, bleach can discolor some surfaces and cause respiratory problems in workers and sensitive populations.

If chemical irritancy is of concern, then newer steam vapor systems may prove valuable, since heat works broadly across most groups of microorganisms.

Careful And Complete Cleaning

Another main reason disinfectants sometimes fail in the field is that staffs simply don''t clean all the surfaces.

A recent study published in 2008 by Carling et al. from Caritas Carney Hospital reported that, on average, 49 percent of frequently touched surfaces in 23 acute care hospitals were not cleaned during terminal cleaning.

Because terminal cleaning and disinfection are well understood, it is reasonable to think the Carling study is representative of nationwide practices and that about half of surfaces that should be cleaned in health care facilities are regularly skipped or missed.

This suggests missed areas may be a major cause of disinfection failures in the field.

New whole-room chemical fogging and ultraviolet (UV) light disinfection technologies may provide a solution to the problem of surfaces skipped during cleaning.

Chemical fogging, such as with hydrogen peroxide gas, carries the advantage of disinfecting all surfaces in a room at once.

One well-studied device uses a pulsed UV technology to decontaminate rooms in minutes.

Laboratory and hospital studies indicate that even indirect exposure of surfaces to the pulsed UV light carries a substantial sanitization benefit.

Both of these new technologies will sanitize easy-to-miss surfaces, but both must be used in combination with cleaning since neither has the benefit of soil removal.

To help control outbreaks within facilities, cleaning professionals would do well to focus on the efficacy of the methods and technologies they are using to control pathogens.

Given the challenges of achieving consistent and effective surface disinfection using traditional liquid disinfectants alone, complementing these approaches with newer technologies may provide a valuable integrated solution to help protect public health better than any one method in isolation.

Dr. Benjamin Tanner is the principal of Antimicrobial Test Laboratories, an independent testing facility specializing in the research and development of antimicrobials, including disinfectants. Dr. Tanner holds a B.S. in Molecular Biology and a Ph.D. in Microbiology and Immunology from the University of Arizona, where he studied environmentally mediated disease transmission and assessed infection risks for workers.

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