Fomite Transmission Among Respiratory Viruses and the Importance of Low-level Surface Disinfection

Respiratory virus infection is likely to result from all three major modes of transmission: contact (direct or indirect), droplets, and aerosols (3). However, we do not have a strong evidence base for our understanding of transmission and prevention of these viruses. This lack of knowledge is underscored by the wide variability of transmission-based prevention measures outlined by the Centers for Disease Control and Prevention (CDC) in hospital settings – variability even for the same organism (4). For example, adenovirus pneumonia, a lower respiratory tract infection, is documented as needing droplet precautions, but upper respiratory infection, or other lower respiratory infections (exacerbation of chronic bronchitis or acute bronchitis) are not specifically mentioned. This results in a recommendation for transmission prevention under “respiratory infectious diseases not covered elsewhere” – suggesting that only standard precautions are needed. The lack of specific published evidence for transmission prevention of this virus results in confusing guidance, which may lead to difficulty in implementing prevention interventions in practice. Further, this may erode trust in those attempting to implement interventions if said interventions compete with one another. A more practical approach is to institute protections to reduce the risk from all major sources of potential transmission. This approach is called the “swiss cheese model” and is often considered the cornerstone of quality (5, 6). In healthcare, this approach led to the consideration that ‘bundles’ of interventions may be the most effective approach for infection prevention in most settings.

This bundled intervention approach is a necessity, as all three transmission modalities are likely common for all respiratory viruses (3, 7). This probability is often conflated with the ‘primary’ mode of transmission – the mechanism by which ‘most’ infections occur. Since a primary mode of transmission is nearly impossible to define outside of controlled laboratory experiments non-generalizable to community health settings, public health policy must focus on interventions to control all potential transmission modalities. The reality is that multifaceted interventions are necessary to curb the spread of nearly all transmissible infectious agents. Differentiating the likelihood of various modes is often more of an academic exercise than a public health necessity in many situations.

Of these three modes of transmission, droplet and aerosol routes are regularly discussed in the field of respiratory viruses and have dominated nearly all prevention discussions with respect to SARS-CoV-2 (8, 9). Nonetheless, a significant body of evidence exists with respect to environmental longevity of respiratory viruses and their potential for indirect transmission via fomites (10-30). Despite this longstanding knowledge, there is often limited consideration for the importance of these inanimate surfaces in respiratory virus transmission prevention. This is exemplified by the occasional minimization of transmission due to fomites in SARS-CoV-2 (31) despite the fact that it may be possible to capture this organism on surfaces more readily than in the air (11), surface contamination is very common (8, 11, 32), and infectious virus appears to persist longer on surfaces than in aerosols (8). Even recently, the CDC has reduced the importance of surface transmission and hand hygiene, an elementary mistake in situations of high public health importance. Fomite transmission is a critical concept since it is not possible to decouple these transmission mechanisms given that contact transmission is tightly interconnected with both droplet and airborne routes. If a particle can be released from an individual via droplets or aerosols and the pathogen contained within the particle can remain infectious on a surface for any amount of time, contact transmission via indirect routes has more than a reasonable potential to occur.

The difficulty in decoupling these transmission modalities results in limited direct evidence for both modes. This issue can be solved through well controlled human-laboratory studies, however. For example, human challenge studies with respiratory viruses result in an ideal scenario to study transmission via various routes. These studies are extremely expensive and difficulty to accomplish and require specific biological safety units which allow infected subjects to stay and be cared for on a 24-hour basis until they are deemed no longer infected. National funding for these studies should be strongly considered to facilitate evidence-based guidance for the next pandemic.

These points drive an argument for policy changes during public health disasters concerning transmissible infectious diseases. When the interventions are simple there should be mandatory multimodal approaches for intervention as without this, not only do our approaches falter, but political agendas may contaminate our ability to protect the public.

Hand hygiene and low-level surface disinfection are the two primary interventions for reducing transmission risks from fomites, both of which are known to have poor compliance in healthcare settings and are therefore likely to be of poor compliance in the community as well (33, 34).  Given the difficulty in monitoring and ensuring compliance with hand hygiene, the importance of surface disinfection has been deemed more and more critical over the past decade (34). Without question, disinfection is a vital component of our multifaceted approach to limit transmission of respiratory viruses. Nevertheless, a major bottleneck with surface disinfection as a transmission reduction intervention is that it is a “momentary event’, and microorganisms rapidly recontaminate the environment after traditional disinfection approaches (35). This means that surfaces need to be disinfected efficaciously with some regularity, a task which is often difficult to implement in practice. Many interventions have been studied to improve cleaning and disinfection processes, ranging from monitoring and feedback (36) to ready-to-use cleaner/disinfectant combinations (37), but limitations remain. Self-disinfecting surfaces have been suggested as potential additive interventions, but most have not proven their cost-benefit to date (38).

Yet another improvement to our surface disinfection interventions may be to add continuously acting disinfectants or antimicrobial surface coatings to compatible surfaces. Several of these products exist, but only a few have shown effectiveness in interventional studies against a variety of pathogens (39-42). Antimicrobial coatings may be advocated as part of an environmental hygiene bundle along with traditional cleaning and disinfection procedures (e.g. daily and terminal cleaning/disinfection of patient rooms). Antimicrobial coatings will also reduce bioburden on surfaces other than the traditional “high touch” areas which are the focus of traditional cleaning and disinfection programs (43). These other surfaces are not often considered as major reservoirs for pathogens. However, risk is a continuum, not a binary event. Therefore, all surfaces touched by individuals may pose a risk for infection, not simply high touch areas near direct patient care activities. The actual risk of acquisition of an infection from a fomite will vary based on the same factors (infectious dose, individuals immunological state, etc.) as risks from direct person-to-person transmission. Antimicrobial coatings may help ensure that these largely ignored surfaces are maintaining a low microbial bioburden, further reducing fomite transmission risks. Antimicrobial coatings may be bacteriostatic or bactericidal, although the end product is one that has some form of ability to maintain pathogen inactivation over some time – in some cases up to 90-days post application. These products do not eliminate the need for regular disinfection activities. Further, they must withstand repeated scrubbing with other cleaners and disinfectants. With only recent movement by the United States Environmental Protection Agency (EPA) to develop testing methodologies to document the efficacy for antimicrobial surface coatings (44), it may be some time before these products are readily available or recommended in US national guidance.

Regardless, these new technologies do show promise for improving our approach to low-level surface disinfection into the future (39-42) and continue to be active areas of research with a great deal of promising data (45, 46).