Few doubt the value of regular surface disinfection in hospitals, schools, and other institutions. However, there is a healthy debate taking place within the environmental services and infection control communities, attempting to address a fundamental conundrum – which surfaces to disinfect, how and how often?
Two questions are central to the first part of the debate. “On which surfaces are pathogens likely to reside?” and “What is the risk associated with different surface types?” While a great deal of scientific information has been generated in this area, and sorting through the science can be challenging, common sense applies.
Typically germs live in moist places and in places frequently touched. Also virtually all studies agree that microorganisms can persist on surfaces for long periods, although on dry and less-frequently touched surfaces, germs are in various stages of dying off (Gram-positive bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcci (VRE), etc. survive much longer on a dry surface than Gram-negative bacteria such as E. coli, Salmonella, etc. Fungi also survive for long periods on dry surfaces, as do bacterial endospores such as Clostridium difficile, etc.)
Since germs eventually die on dry surfaces, and most environmental surfaces are dry, it is reasonable to conclude that wet surfaces and dry surfaces with the high germ deposition rates (a.k.a. high-touch surfaces) will be the most contaminated within any environment.
The Question of Risk
Of course, while microorganisms are ubiquitous on environmental surfaces, not every microorganism has the ability to cause disease. Thus, there is a big difference, from a risk perspective, between a surface contaminated with germs and a surface contaminated with pathogens – microorganisms capable of causing disease.
Also, an environmental surface must be contaminated to contribute to disease transmission, and there must be an opportunity for that contaminant to make the jump from the surface to a person – that is, for a surface to pose a risk, there must be a potential for exposure to the pathogen.
Toilets bowls are highly contaminated, but rarely touched, so they are not high-exposure, high-risk surfaces. Hospital bedrails, door handles, tabletops, IV poles, bedding and other surfaces are a different story; while they may not harbor the same high concentration of pathogens found on a toilet bowl, people do touch such surfaces on a regular basis. Thus, exposure to pathogens on high-touch surfaces is much greater, and therefore the surfaces pose a greater risk to health.
High-touch surfaces have also been identified in recent years as hotspots of surface-mediated pathogen transmission, especially in hospitals.
Thus, since touch points are the intersection where germs reside, stay alive and are easily transmitted, they should be our primary focus; although damp places and germ reservoirs such as sink basins, adjacent countertops, and restroom toilets and floors should also be regularly included in an overall preventive program.
Increasing the Frequency of High-Touch Surface Disinfection
Obviously, the fewer pathogens on a high-touch surface the better. But it is impractical to disinfect a surface every time it is touched. In “real life” most high-touch surfaces are disinfected once a day, at best. Disease transmission by high-touch surfaces could be better controlled by increasing the frequency with which these surfaces are disinfected. However, increasing the frequency of disinfection naturally amplifies the negative attributes of the any disinfection technology (e.g., toxicity, corrosiveness, etc).
Most disinfectant chemicals are respiratory and eye irritants. For the average person, this represents only a minor health risk; for the average hospital patient, however, increasing the disinfection cycle could dramatically increase the chances of chemical irritation.
Chemicals (especially oxidants like bleach) may degrade surfaces over time. Increasing the disinfection interval could increase the rate of surface degradation (yellowing, cracking, etc).
Another problem with increasing the frequency of surface disinfection with chemicals is that during the contact time required for efficacy, the surface becomes unusable. Certainly no one would be happy to touch a door knob covered in soapy quaternary or caustic bleach.
Steam vapor systems offer a unique alternative to chemical disinfectants for surface disinfection. The first and most obvious advantage is the absence of chemicals. Without chemicals, there is no potential for chemical irritation. This means that the technology can be used more frequently to disinfect a high-touch surface, without any risk of increased chemical irritation to sensitive populations.
Another advantage of steam vapor systems for frequent surface disinfection is reduced risk of chemical-related surface degradation. Most high-touch surfaces are very compatible with steam, especially metals and most plastics. The same cannot be said for traditional chemical disinfectants. Increasing the disinfection frequency with harsh chemicals may increase the risk of surface discoloration, residue buildup, or damage.
Steam vapor systems kill pathogens by transferring heat to them on the contaminated surfaces. When thermal energy is delivered efficiently to the surface, disinfection is rapid. Whereas liquid chemical disinfectants require, on average, 5-10 minutes to disinfect surfaces, thermal disinfection takes place in seconds. This is a major advantage for frequent surface disinfection, because the surface stays usable except for the few seconds when it is actually being treated.
One steam vapor system in particular (MondoVap 2400 with TANCS®, Advanced Vapor Technologies, Edmonds, Wash.) has been tested by four separate, independent laboratories, all of which operate to Good Laboratory Practice (GLP) standards. A realistic test system was designed for all studies (many of which were done entirely in duplicate). High initial microbial concentrations were used, dried onto a mix of porous and non-porous hard surfaces. Study results show that the system, when fitted with triangular cleaning attachment, rapidly kills viruses, fungi, and antibiotic-resistant bacteria, providing a sanitizing benefit within two seconds of surface contact and disinfecting surfaces within 5 seconds.1
For more information, visit http://www.antimicrobialtestlaboratories.com/
Benjamin D. Tanner, PhD, is the principal of Antimicrobial Test Laboratories, an independent testing facility specializing in the research and development of antimicrobials, including disinfectants. Tanner holds a BS in molecular biology and a PhD in microbiology and Immunology from the University of Arizona, where he studied environmentally mediated disease transmission and assessed infection risks for workers.
1. Tanner BD. Reduction in infection risks through treatment of microbially contaminated Surfaces with a novel, portable steam vapor disinfection system. Am J Infect Control. 2009. 37(1):20-27.