The Future of Well-being is Residual: A New Era of Cleaning and Public Health

Introduction

In a world where disease prevention hinges on the battle against invisible microbes, the advent of residual sanitizers to augment traditional disinfection offers a promising and powerful weapon to revolutionize our approach to public health and cleanliness.

Since before World War 2, disinfection has been relied upon to control pathogens and harmful microbes on surfaces. The battle against organisms is an essential aspect of public well-being, and surface disinfection approaches are well-entrenched in society. Yet even today, it is estimated that at least 3 million people in the United States alone are infected by preventable pathogenic infections every year¹. Clearly, the current approach to disinfection is falling short of its promise. One primary reason is that disinfectants stop working the moment they dry or are wiped away from a surface. Once dry, surfaces are immediately susceptible to re-contamination by touch, a nearby cough, or the settling of airborne microorganisms, enabling the transmission cycle to begin again when someone touches the surface. More frequent cleaning and disinfecting can lessen transmission, but with the trade-off of increased labor, more chemical usage, and inconvenient disruption. For many frequently touched surfaces, like doorknobs and ATM screens, “more frequent cleaning” can be virtually impossible to implement.

In the past few years, new approaches have been taken to re-invent the technology behind traditional cleaning and disinfecting products. These products provide a strong germ-killing effect while leaving behind an invisible layer of protection to keep surfaces microbe-free between cleaning events. Ultimately, this new class of antimicrobials interrupt the cycle of rapid re-contamination in a single application, reducing the consumption of chemicals while achieving their main objective to improve public health and wellbeing.

 How are germs transmitted?

Germs are microorganisms that cause illness. They come in the form of bacteria, viruses, fungi, and protozoa and can be found in any environment you can imagine. Germs are spread through direct and indirect contact. Direct contact is exactly as it sounds, making physical contact with someone who is infected. Indirect contact can occur through droplets, aerosols, or fomites. Droplets and aerosols are common transmission routes for respiratory viruses like the seasonal flu and even SARS-CoV-2². Droplets are larger, heavier particles that usually fall onto nearby surfaces, whereas aerosols are fine particles that can stay suspended in the air for extended periods of time. Droplets and aerosols are generated from infected people when they sneeze, cough, or even speak. Fomites represent inanimate objects that germs land on³. Almost every surface can be thought of as a fomite and can therefore serve as a source of germ transmission. There have been many attempts to understand the specific role that each of these transmission pathways plays in the spread of germs. The complexity of these events has led to insufficient evidence to support one of these mechanisms as the lead contributor to germ transmission⁴.

Almost every surface can be thought of as a fomite and can therefore serve as a source of germ transmission

Although there is inconclusive evidence for which factor has the greatest impact on human disease transmission, fomites (surfaces) have long been acknowledged as a contributing factor. The importance of surfaces in transmission originates from the ability of microorganisms to survive and potentially remain infectious for surprisingly long periods of time. Depending on the environmental conditions, bacteria and viruses can persist on surfaces for months⁵. Additionally, it has been determined through experimentation and observation that surfaces have been the source of infection^6,7. It stands to reason that if one of the primary transmission routes for germs can be interrupted, there would be a reduction in illness and infections. Being that surfaces are ubiquitous in the human environment and that aerosols and droplets have a chance to land on and contaminate them, surfaces represent an ideal target for intervention.

The distinction between cleaning, sanitizing, and disinfecting

Cleaning refers to the physical removal of oils, dirt, and dust from surfaces. Cleaners often do not contain ingredients known to kill microorganisms. In contrast, both sanitizers and disinfectants demonstrate some level of microbial kill. Sanitizers and disinfectants are also usually effective cleaners therefore, these products physically remove oils, dirt, and dust from surfaces and reduce the number of organisms. It is common to refer to these types of sanitizers and disinfectants as “one-step,” meaning that they can both clean and reduce the number of microbes.

Broadly speaking, both sanitizers and disinfectants kill microorganisms, but disinfectants demonstrate a larger reduction in the number of organisms. The United States Environmental Protection Agency (US EPA) regulates sanitizers and disinfectants and therefore defines their performance standards. On hard, non-food contact surfaces, sanitizers must demonstrate a 99.9% reduction against bacteria in 5 minutes⁸. Put another way, this means that the number of bacteria on a surface is reduced from 100,000 to 100. On the other hand, disinfectants must demonstrate a 99.999% reduction against bacteria in 10 minutes; or reduce the bacteria on a hard, non-food contact surface from 100,000 to 1⁹. Additionally, disinfectants can be evaluated for their ability to inactivate viruses; an attribute that will soon be extended to sanitizers¹⁰.

Knowing when it is necessary to implement cleaning, sanitizing, or disinfecting practices is not always straightforward. The type of space and its occupants are critical factors that influence determining the appropriate practice. The Centers for Disease Control and Prevention recommends routine cleaning of frequently touched surfaces with soap and water to remove oils, dirt, and dust¹¹. In most households, cleaning combined with routine sanitization of surfaces is sufficient to reduce the bioburden present in this setting. However, there are certain circumstances that would elevate the requirement for disinfection; for example, if someone in the household is actively sick, surfaces they interact with should be disinfected to reduce the likelihood that other occupants get infected¹¹. In places with large amounts of human traffic (office buildings, entertainment facilities, or schools), cleaning in combination with routine disinfection of communal surfaces may be an appropriate regimen to keep the number of microorganisms present to a minimum. The large number of occupants in these settings leads to increased accumulation of bacteria and viruses on surfaces necessitating the kill level of a disinfectant. The healthcare industry has more rigorous cleaning standards than those required in homes or businesses. There are often mandated protocols and practices that hospital systems implement in an effort to mitigate the spread of infections. Disinfection is the minimum requirement for hard surfaces; sanitizers are rarely used in healthcare settings as they do not provide sufficient microbial kill to meet their cleaning standards¹².

Alternatives to traditional antimicrobial practices

An inherent property of traditional sanitizers and disinfectants is that they only exert their effect while the surface is wet with the product. Once the liquid is wiped off the surface or dries, it no longer kills microbes. To add a layer of complexity, the duration that a surface needs to remain wet with the product to meet sanitization or disinfection criteria is different for each product and can range from as little as 30 seconds to as long as 10 minutes; this is referred to as the contact time. In locations where multiple sanitization or disinfection events are necessary in a single day, adherence to the prescribed contact time leads to repeated exposure to chemicals, increased use of paper and cloth wipes, and significant time and labor commitments. These drawbacks highlight the need for alternatives to traditional means of sanitization and disinfection.

Over the past few decades, there has been a focus on the development of suitable alternatives to traditional sanitization and disinfection. One of the primary goals of these alternatives is to improve upon the key limitations of sanitizers and disinfectants, specifically that they only actively kill microbes while the surface is wet. Therefore, the key attribute of these products is that they maintain some level of antimicrobial activity after they have dried, forming a protective coating on the surface. These types of antimicrobial products are generally referred to as continuously active, long-lasting, persistent, or residual antimicrobial coatings.

Some of the earliest examples of products applying this concept utilized the elements copper and silver. Both metals are inherently antimicrobial and have activity against both bacteria and viruses¹³. Copper is exceptionally strong and can withstand the normal wear and tear of a heavily used surface while maintaining its antimicrobial properties. Silver has been incorporated into many consumer products, including home appliances, fabrics, toys, and even medical devices. Although copper and silver fit the criteria of maintaining an antimicrobial effect after drying, they also have their own limitations. The incorporation of these metals into objects or onto surfaces is not a simple process that can be carried out by the end user, this usually needs to be accomplished as part of manufacturing. Additionally, the amount of time (contact time) it takes for these metals to impart their antimicrobial effect is typically longer than that of traditional sanitizers and disinfectants, meaning that their activity is not as robust as the traditional interventions. Nevertheless, the continuous antimicrobial activity of these metals has proven valuable in healthcare settings^{13, 14}.

Another approach to achieving a long-lasting antimicrobial effect is the incorporation of chemical preservatives into materials. These chemicals can be integrated into a wide variety of materials during the manufacturing process, including but not limited to hardwood floors, doorknobs, fabrics, plastics, and paints¹⁵. Materials with an embedded chemical preservative are sometimes categorized as treated articles. The chemical preservatives incorporated into treated articles are not as strong as those found in traditional products and only prevent the development of odors and deterioration caused by certain bacteria and fungi. Therefore, an important distinction must be made between treated articles and the concept of sanitization and disinfection: the article itself is being protected from microbes rather than the surface of that article providing an antimicrobial barrier that can have a positive impact on human health.

newer solutions utilize polymer chemistry to create a micro-structure on surfaces

More recently, a new strategy is being explored to overcome the limitations of the first iterations of long-lasting antimicrobial products. These newer solutions utilize polymer chemistry to create a micro-structure on surfaces that active ingredients stick to, allowing them to persist on the surface after it has dried. The first generation of this attempt at a long-lasting antimicrobial is classified as microbiostatic agents. The antimicrobial effect of these products is stronger than treated articles but has limited killing capacity. Microbiostatic products prevent the growth of bacteria as opposed to killing them and cannot market that they provide a public health benefit^{16, 17}. The next generation of long-lasting antimicrobials has built upon the strides that microbiostatic products have made in the industry. These technologies have optimized polymer systems that incorporate the types of active ingredients commonly found in traditional sanitizers and disinfectants. The inclusion of stronger active ingredients boosts their performance and allows them to state they provide a public health benefit as long as certain US EPA requirements are met.

Types of residual antimicrobials and how they are regulated

During the COVID-19 pandemic, the antimicrobial market was flooded with many products claiming to provide long-term disinfection. However, only a limited number of these products had their claims registered with the US EPA. This prompted the EPA to issue guidance to stakeholders on the requirements for adding residual claims to EPA-registered products¹⁸. Currently, the EPA recognizes three categories of residual antimicrobials: residual sanitizers, residual disinfectants, and supplemental residual antimicrobials. The first two categories existed prior to the COVID-19 pandemic, while the last was established during the pandemic.

The specific testing protocols and performance requirements differ between the three residual antimicrobial categories. However, the key performance metric across all categories is to demonstrate that a product maintains a certain level of antimicrobial activity after being subjected to physical abrasion. This abrasion regimen is a simulation of the physical wear and tear a surface would encounter over the duration of the residual efficacy period. A brief description of the performance requirements and real-world application for each category is provided below.

Residual Sanitizers

Products that fall under the residual sanitizer category must first meet EPA’s criteria for a traditional sanitizer (99.9% reduction against bacteria within 5 minutes). If this criterion is achieved, the residual activity is evaluated through a series of alternating wet and dry abrasions paired with multiple contamination events (introduction of bacteria to the test surface between abrasion events)¹⁹. At the conclusion of the durability assessment, the product must again demonstrate a 99.9% reduction against bacteria in 5 minutes. Currently, the duration of residual sanitization claims is limited to 24 hours. In a real-world scenario, this means that after the product is sprayed onto a hard, non-food contact surface and dries, it maintains sanitization-level efficacy against bacteria for 24 hours in just one application.

Residual Disinfectants

The testing parameters for residual disinfectants are similar to residual sanitizers. However, the performance requirements are harder to achieve for disinfectants because a higher level of kill is required. Residual disinfectant products must first meet EPA’s criteria for a traditional disinfectant (99.999% reduction against bacteria within 10 minutes). If this criterion is achieved, the residual activity is evaluated following a procedure similar to what is used to evaluate residual sanitizers¹⁹. At the conclusion of the durability assessment, the product must again demonstrate a 99.999% reduction against bacteria in 10 minutes. Unlike residual sanitizers, residual disinfectants can also have residual activity against viruses, provided they have durability data to support the notion¹⁸. Currently, the duration of residual disinfection claims is limited to 24 hours. In practice this means that after the product is sprayed onto a hard, non-food contact surface and dries it maintains disinfection-level efficacy against bacteria and viruses for 24 hours in just one application.

Supplemental Residual Antimicrobials

The testing parameters for the final category of residuals, supplemental residual antimicrobials, differ from residual sanitizers and disinfectants. Abrasions remain a key component of the assessment; however, these products are not required to meet the performance criteria of a traditional sanitizer or disinfectant. This is a key component of the guidance for these products because they are intended to be a supplement to normal disinfection practices. The durability assessment for these products requires that the supplemental residual antimicrobial coatings be exposed to three different disinfectant-level products¹⁸. At the conclusion of the abrasion procedure, sanitizer-level efficacy must be demonstrated within 2 hours. Like residual disinfectants, supplemental residual products may also have activity against viruses, if appropriate data are generated. The duration of this type of residual claim is 7 days, meaning that with one application these products retain sanitization-level efficacy for one week and will not wear off the surface if it is routinely disinfected.

Although the US EPA standardizes the performance criteria of residual products, it is not always easy to determine the performance level of a product just by reading the label. Some EPA-registered products are marketed for providing a long-term antimicrobial benefit, but these do not fit the definition of residual antimicrobial as defined by EPA. They often belong to the microbiostatic category described above where they only prevent the growth of bacteria and fungi that can cause malodor and stains and cannot state they provide public-health benefits. Therefore, it is important to understand what a specific product can achieve by reading its label. Every product registered with the EPA is assigned a unique number that is linked to a document stating the specific efficacy requirements it meets²⁰. Searching this product-specific document for keywords like “residual sanitizer” is an effective way to confirm a product is a legitimate residual antimicrobial.

How will residual antimicrobials change the way we clean?

Continuous protection of surfaces against becoming a hotspot for germ transmission is a crucial development for advancing public health and disease prevention. Some of the first-generation residual antimicrobials have been put to the test in clinical settings to ascertain if they do indeed provide a benefit to public health. Not surprisingly, use of these persistent antimicrobials was associated with a decrease in the number of bacteria isolated from surfaces as well as reduced infection rates in hospitals^{21, 22}. This evidence highlights the benefit and need for alternative strategies to traditional methods of disinfection that can enhance infection prevention. Next-generation residual antimicrobials meet much higher performance standards than their predecessors and are designed to withstand the wear and tear associated with daily use. These aspects should only increase their potential as worthwhile mechanisms to increase safety through a reduction in surface-based germ transmission.

In addition to the major upside of reducing germ transmission, residual antimicrobials offer substantial financial and time savings. The persistent nature of residual sanitizers and disinfectants allows their application to be limited to once a day. During this 24-hour period, occupants of the treated space are assured that those surfaces are actively killing bacteria (or viruses) that happen to land on the surface with just a single application of the product. By transitioning to the use of these products, companies and consumers can significantly reduce costs associated with cleaning chemicals, single-use paper products, and labor while gaining valuable time.

As public health awareness rises, the demand for continuous antimicrobial protection has reached an all-time high. Outdated methods no longer suffice as the standard for maintaining a healthy life and ensuring the well-being of our families and workplaces. This is especially true in the context of antibiotic resistance where the development of resistance to current pharmaceutical antibiotic therapies significantly outpaces the implementation of new drugs to treat these infections¹. It is critical that other methods of intervention be deployed to compensate for the limitations of pharmaceuticals. Residual antimicrobials, with their ability to provide long-lasting protection, are poised to become the new standard in cleaning technology, shaping a healthier future for all.

References

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