Characteristics of an Ideal Surface Damage Testing Protocol

By Peter Teska, MBA; John Howarter, PhD; Haley Oliver, PhD; Jim Gauthier, CIC; Kay Bixler; and Xiaobao Li, PhD

The importance of a hygienic patient environment of care has been demonstrated repeatedly in the literature (Weber, 2010) (Han, 2015). Studies of commonly touched environmental surfaces and patient care equipment (i.e. high touch surfaces) have detected pathogenic microorganisms at epidemiologically significant levels (Weber, 2010) (Weber, 2013) (Han, 2015). Studies of patient room occupancy and infection rates have found higher infection rates from environmentally transmissible pathogens based on the infection status of the prior patient in the room (Ajao, 2013) (Huang, 2006) (Drees, 2008) (Nseir, 2011) (Shaughnessy, 2011); thus routine cleaning and disinfection is an important part of infection prevention for healthcare facilities.

The CDC recommends that high-touch surfaces be cleaned and disinfected on a routine basis (Sehulster, 2004), ranging from daily to several times per week depending on the perceived risk and level of soiling that occurs on the surface. Portable equipment transferred between patient rooms requires disinfection among rooms up to several times per hour, to reduce the risk of pathogen transmission.

While the materials selected for environmental surfaces and patient care equipment should be capable of being disinfected without loss of functionality (Ontario Agency for Health Protection and Promotion, 2013), there is no standardized method for a manufacturer to make this determination, nor agreement on the material functionality parameters that should be measured to determine whether surface damage has occurred. Furthermore, it is important to note that types of surface damage can occur to a material without necessarily inducing a "loss of functionality." A simple example would be a monitor where the housing became scratched or changed color over time, but the scratches and color change did not affect the ability to use the monitor and it still ‘functions’ as intended. Such disconnection among surface damage, disinfection practice, and equipment functionality poses a previously uncharacterized risk for infection prevention.

The chemistries used for cleaning and disinfection products in healthcare can have a negative effect on the integrity of the surfaces and equipment, but there is no standard methodology to measure this impact. Similarly, the mechanical action introduced by the wiping cloth may also have a detrimental effect on surfaces, but a standard methodology or evaluation criteria to measure such impact is still lacking. A new ASTM method, E2967-15 (ASTM International, 2015) standardizes the pressure and contact of a disinfectant wipe, using brushed stainless steel discs, but this method is validated only for prewetted disinfectant wipes, and not for cotton or microfiber wiping cloths.

All manufacturers of patient-care equipment should provide instructions for use (IFU) that list compatible disinfectants for cleaning equipment. However the compatibility testing is not standardized across the industry, does not use validated methods, does not generally include newer disinfectant technologies, often is only qualitative, and may only list active ingredients which does not take into account the other ingredients in a disinfectant that may cause surface damage. This makes it challenging to compare surface damage information among disinfectant manufacturers and equipment manufacturers. In some cases, equipment manufacturers list ingredients not compatible with their equipment in the IFU, yet recommend disinfectants including the same ingredients, resulting in confusion for healthcare facilities to evaluate and choose disinfectant products.

It is difficult to predict the clinical impact of surface damage because there is no clear definition of what constitutes surface damage. In theory, surface damage can cause equipment to fail to operate correctly and can shelter microorganisms, thus preventing proper disinfection. Both types of surface damage can create safety risks for patients and staff in healthcare facilities.

To facilitate the discussion below, surface damage is defined as a quantifiable physical or chemical change from the original manufactured state of an object (surface or device). Surface damage that results in aesthetic changes, such as color loss or change in color, may not affect the performance of the equipment and thus may not be of any clinical significance. However, to some users, color variation would be evidence of surface damage and thus may indicate that an object may need to be replaced. In some cases, residual from the disinfectant may leave a visible residue on surfaces. This creates an aesthetic worsening of the surface appearance, but often this residual is removable and does not indicate permanent damage to the surface. For purposes of this discussion, color change that is only aesthetic in nature and removable residual from the disinfectant are not considered forms of surface damage.

We recommend using surface roughness as an appropriate parameter to determine surface damage. Changes in surface roughness can indicate a loss of material from the surface, an increase in the number of cracks or fissures, or irreversible changes in the chemical bonding in organic surface materials, which can change the performance of the surface. The link between surface roughness and microbial risks has been explored by previous studies. Verran and Boyd (2001) reviewed data showing that surface roughness can create defects in the surface that provide protection from shear forces, such as from cleaning, and may provide more secure adhesion points for bacteria. Aykent (2010) from the field of dental finishing showed that the number of bacteria on a surface was positively correlated with the surface roughness. Gonzalez (2017) showed that rougher surfaces were harder to clean of blood soil, but did not quantify the degree of surface roughness necessary to see this difference. Notably, the size scale of the change in surface roughness is often below the detection limit of humans via sight or touch.

Surface damage can make it more difficult to disinfect a surface or create some other definable safety risks (such as surface damage exposing wiring or cracking tubing), both of which have clinical significance. When surface damage is minor, it may be detectable, but not have achieved any clinical significance. However, if the surface damage continues, it may reach a point of clinical significance at some later time. Even minor surface damage should be considered important because of the potential for surface damage to reach the threshold point. Therefore, surface roughness, which is related to the ability to disinfect the surface, is an appropriate parameter to address the question of proper disinfection to avoid surface damage, although what constitutes significant damage remains undetermined at this point (Sattar, 2013.)

Ideally, a detector should be placed on a surface in question and by pressing a button, quantitative data would be generated that would compare the original condition of the surface to the changes in the surface over time. Using a database of information tested using this method, it would be possible to quantify the amount of additional risk associated with the degree of damage. However, no such device or database exists today.

The field of materials science has worked extensively on methods to characterize surfaces. What makes this characterization valuable is the ability to tie the characterization method to a specific parameter (or parameters) that allow for differentiation among surfaces in a meaningful manner. It is unlikely that a single test would allow for a relevant determination of surface damage. It would either be too sensitive, identifying surfaces as damaged that do not have clinically relevant damage, or conversely it would only identify surface damage when it was so extreme that the surface could no longer be used. It is important to address this concern, as it relates to healthcare surfaces and the disinfectants and wiping cloths used on them. In this article, we identified relevant criteria that would allow for the selection of an appropriate testing methodology to identify surface damage.

Based on the evaluation criteria discussed above, we believe that applying the disinfectant through wiping and allowing the surface to air dry is an appropriate methodology. A four-pass wiping method (left, right, left, right) would provide adequate contact between the surface and the disinfectant chemical and factor in the wiping cloth impact as well and is consistent with the current EPA wipes test method. The surface should be allowed to air dry for a defined period of time, such as 10 minutes, before reapplication of the product. This process should be repeated 200 times to simulate the damage that could occur by disinfecting the surface daily for six months. Other numbers of repetition may be just as predictive of surface damage, but 200 cycles should be representative of any likely damage due to normal use.

Surfaces roughly two inches wide by 12 inches long would be appropriate during this sample preparation. The sample after disinfection wiping can be cut into appropriate pieces for testing. All testing should be run in triplicate.

It may be desirable to additionally test samples immersed in disinfectant chemicals for a period of time but this would only be done as part of over-testing and would not replace the standard wiping method of application. Immersion, while not reflective of the type of exposure for surfaces from normal use of disinfectants, can provide an indicator of what surface damage a worst-case exposure might be expected to cause. If standard wiping and immersion both do not show any significant surface damage, then this provides strong evidence that the disinfectant/surface combination are not likely to cause surface damage under normal use or under extreme exposure conditions.

To be an appropriate method to characterize surface damage for healthcare surfaces, the testing should address these criteria:
1. The sample preparation and testing should simulate how a product is used. Some manufacturers immerse coupons of material in disinfectant. This type of exposure is likely to be much more extreme than how disinfectants are used in practice and can introduce additional variables, such as the impact on the cut edges of the material, which would not be present in the surface as used.
2. The testing should not introduce additional exposure variables that are not customarily present. The use of heat or wrapping a wipe on a sample of the surface both introduce additional variables not present under normal use. If testing under conditions that introduce additional variables also demonstrates that there is no additional impact, it may be possible to introduce factors such as these as part off the testing methodology, but a substantial dataset would be needed to ensure that these factors did not introduce additional variables not present under normal use.
3. While some of the surface damage characterization methods may be qualitative, an appropriate test must include a strong quantitative component, which allows for determining the degree of damage.
4. The testing should differentiate different degrees of surface damage in a meaningful way. It should determine the degree of surface damage using quantitative measures and allow for differentiation between damaged and undamaged surfaces, consistent with how surfaces perform by measuring characteristics that are critical to real world performance of the surface.
5. The field of materials science groups testing methodologies into macroscopic, microscopic, and spectroscopic methods. The proposed panel of testing should include at least one test method from each category for a comprehensive assessment. The testing should not solely rely on macroscopic testing of bulk samples of the material, such as “dog bone” stress testing. While changes in material strength are evidence of surface damage, microscopic and spectroscopic methods are much more likely to show surface damage before it is detectable at the macroscopic level.
6. The methods should be reproducible with an easy replicate testing methodology so that results in different labs would be consistent.
7. The characterization should measure more than one parameter of surface damage. If the surface changes in size, weight, or roughness, all these attributes would be important considerations and methods of characterization on these attributes should be applied.
8. The sample damage should simulate a defined amount of time in real world application, such as 6 months. If the sample damage was continued to simulate a longer period of time, such as 1 year, the one year damage may be twice the 6 month damage, but it remains to be shown that the damage is linear over longer periods of time.
9. The method might allow for a measurement that simulates worst case condition not likely to occur in the real world to show how extreme surface damage might occur under certain rare conditions.
10. Because residual from the disinfectant may impact the characterization, samples of the material should be tested after disinfectant application (see below) and then repeated after thorough rinsing of the surface, which allows for a more accurate characterization of the underlying surface and allows for characterizing the impact of the disinfectant residual.

Based on the aforementioned proposed criteria, we believe the following panel illustrates a set of appropriate methods for characterization of surface damage. The testing areas are in the order of increasing complexity.
1. Weight change. This quantitative macroscopic test method determines whether a detectible amount of material from the sample is removed.
2. Optical microscopy. This qualitative imaging method identifies the extreme cases of changes in physical surface morphology (i.e. scratches) and can be done quickly and inexpensively.
3. Fourier-Transform Infrared Spectroscopy (FTIR). This qualitative spectroscopic method determines chemical interaction between the residual from the disinfectant and the surface.
4. Contact Angle. This quantitative microscopic method determines surface roughness by measuring the angle formed by a drop of water placed on the surface. Contact angle is an indicator of both surface energy and surface roughness. Smooth surfaces have a low contact angle while rough surfaces have a high contact angle. By comparing the roughness before and after exposure to disinfectant, the change of the surface roughness can be characterized.
5. Atomic Force Microscopy. This quantitative microscopic method allows for various measurements of surface roughness. By comparing the roughness before and after exposure to disinfectant, the degree of change of the surface roughness can be characterized.
6. Mechanical Stress Test (optional). This quantitative measurement uses a standard force to apply stress to a sample of the material. Changes in the force needed to stress the sample indicate surface damage has occurred and has impacted one of the strength measurements of the material. Additionally, by inducing the surface to crack, the test gives a measurement of fracture toughness in addition to mechanical resilience.

Until more robust databases of testing results are available, the results from the testing should be interpreted in relation to the untreated samples of material. Using quantitative approaches, changes in roughness, weight or contact angle can be presented as a percent change from the original state.

Peter Teska, MBA, is with Diversey;  John Howarter, PhD, is from Purdue University; Haley Oliver, PhD, is from Purdue University; Jim Gauthier, CIC, is with Diversey; Kay Bixler is with Diversey; and Xiaobao Li, PhD, is with Diversey.

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