19 minute read
Decoding Dental Aerosols in the Age of COVID-19
Anthony D. Mair, DDS, MCID; Paul H. Korne, DDS, MCID; and Mohamed-Nur Abdallah, BDS, MSc, PhD
ABSTRACT The conflation with medical aerosols in the age of COVID-19 has created an inaccurate and potentially dangerous argument in dentistry.
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AUTHORS
Anthony D. Mair, DDS, MCID, is an adjunct professor in graduate orthodontics at Western University in London, Ontario, and a clinical associate in graduate orthodontics at the University of Toronto. He is a past president of the Ontario Association of Orthodontists. Conflict of Interest Disclosure: None reported.
Paul H. Korne, DDS, MCID, is a faculty lecturer at McGill University in Montreal. He is a past president and member of the Canadian Association of Orthodontists. Conflict of Interest Disclosure: None reported.
Mohamed-Nur Abdallah, BDS, MSc, PhD, is an orthodontics and dentofacial orthopedics resident at the Faculty of Dentistry at the University of Toronto. Conflict of Interest Disclosure: None reported.
The outbreak of SARS-CoV-2 has negatively impacted society over the past few months. [1] The shutting of economies and the introduction of “physical distancing” was a necessary response to reduce the rate of new infections and prevent overloading of our health care systems. As such, dental clinics, along with most other nonessential businesses, were asked to cease operations to reduce social contacts and, in turn, protect the public.
In North America, dental offices are undergoing phased reopening. It is at this critical juncture that a new controversy has risen to prominence — the possible risk of dental aerosols and aerosol-generating dental procedures (AGDPs). [2] In the past few months, some members of the dental community have expressed concern that AGDPs could facilitate the infective transmission of SARS-CoV-2 and endanger dental staff and patients. [3]
Virus Transmission Versus Disease Infection
SARS-CoV-2 is the causative virus for the resultant disease COVID-19. It is important to note that transmission is necessary for infection, but infection does not inevitably follow exposure. [4,5] It is established that SARS-CoV-2 can infect a host via droplet and, to a lesser degree, contact transmission, whereas acquiring COVID-19 disease via airborne transmission remains unlikely. [1,2,5–8]
The viral load can be defined as the number of viral particles in a given volume of droplets. The minimal infective dose is the lowest number of viral particles that can initiate disease. [4,5,9] The minimal infective dose for each virus varies with host susceptibility and immune response. Furthermore, it has been shown that the probability of getting infected as well as the severity of disease are dose-dependent. [4,5,9,10] However, the minimal infective dose for SARSCoV-2 is not well established. [5] Accordingly, it is important to protect the susceptible portals of entry. SARS-CoV-2 enters the human body through the mucus membranes: the nose, the mouth and the eyes. [3,11–13] Therefore, one should shield these areas with appropriate personal protective equipment (PPE).
Aerosols: Droplet, Contact and Airborne Transmission
Many of the following terms are often used interchangeably: “aerosols,” “droplets,” “droplet nuclei,” “airborne” and “solid particulates.” This makes it more difficult to draw recommendations on how to adapt clinical practice.
In general, aerosols are solid or liquid particles that are suspended in the air; while they can be visible, most often they are not. [9,14,15] Aerosols can be divided into large droplets and small droplets. Researchers and clinicians tend to reserve the term aerosol only for small droplets. In this instance, they would use the term droplet for larger droplets and the term aerosols for smaller droplets. Large droplets behave ballistically and tend to be falling when they infect the recipient. This mode of transmission is known as droplet transmission. [5] Large droplets may also contaminate objects and be transferred to mucous membranes by way of touch. This is called contact transmission. 16 Small droplets stay suspended in the air for a variable amount of time or they evaporate and change into a solid particulate droplet nuclei that float freely. The transmission of these small droplets is known as airborne transmission. [8,14,15] Examples of diseases with established airborne transmission include tuberculosis and measles. [17,18] There is significant controversy regarding the cut-off point between small and large droplets. [4,5,14,15,19,20]
Aerosol-Generating Procedures
An aerosol-generating procedure (AGP) is a medical or dental intervention that has the potential of creating aerosols in addition to those that patients naturally produce during breathing, speaking, sneezing and coughing. [14,20] AGPs produce both small and large droplets, and each AGP creates a different pattern and composition of aerosols. Therefore, the term AGP should not be used loosely, and one should not presume that all AGPs have the same risk or require the same level of PPE (i.e., an AGP does not indicate by default a high-risk procedure). The decision to categorize an AGP as a high-risk procedure should be based on evidence. [14] Furthermore, it is inaccurate to conclude that generating aerosols will always cause infection. It is also inaccurate to grant equivalency between aerosolgenerating medical procedures (AGMPs) and AGDPs. The aerosol composition differs considerably even among AGMPs. For instance, certain AGMPs generate aerosols by inducing the patient to cough. It has been shown that coughing emits up to 1,000 times the number of droplets compared to normal breathing. [19]
Aerosol-Generating Medical Procedures
Generally, AGMPs can be divided into two categories: procedures that induce the patient to produce aerosols and those that mechanically create aerosols. [14] Medical procedures that agitate the airway (hereinafter referred as agitative AGMPs), such as tracheal and bronchial intubation, may induce the patient to cough forcibly, thereby releasing aerosols filled with a high viral infectious dose. [14,21] Indeed, both these procedures have been associated with a high risk of SARS-CoV-1 transmission to health care workers. [5,14] For example, a retrospective cohort study reported an increased risk of being infected with SARS-CoV-1 in health care staff involved with intubation procedures. [22] It should be noted that while all health care workers wore N95 masks, some of them did not have eye protection. [22]
In contrast, AGMPs may also disperse aerosols mechanically through interventions such as ventilation, suctioning or nebulizer treatment. Despite the limited evidence, these procedures are generally considered less risky than the induction group described above. [5,14,21,23] For example, a meta-analysis of three cohort studies concluded that nebulizer treatment had no significant increased risk in the transmission of SARSCoV-1 to health care workers. [21]
Hospitals adopted more stringent PPE protocols and airborne precautions to reduce morbidity and mortality when medical health care workers were exposed to agitative AGMPs. [14,24,25] In medicine, not all AGMPs require this higher level of intervention. [21,26] This selective approach to PPE continues now during the COVID-19 pandemic. [26–30]
Aerosol-Generating Dental Procedures
Dental aerosols have been studied for well over 50 years. The tissues and fluids of the oral cavity are replete with bacteria and viruses. [31–34] When the oral cavity is exposed to instruments that rotate, vibrate or expel compressed air, an aerosol of these microbes is inevitably created. [33,35,36] It is also well established in the literature that the attentive use of high-volume evacuation (HVE) will reduce dental aerosols by at least 90%. [37–39] It is important to note here that most hospital suction units are not rated as high volume. 33 The majority of dental aerosol droplets that escape HVE land innocuously on the patient’s face or body. [40–42] A smaller percentage of these droplets constitute the dental aerosol that remains suspended in the air for 10–30 minutes, depending on the airflow characteristics of the operatory. [31]
Many studies have examined the relative infectivity of dental aerosols as well as the risk of crosscontamination in dental settings. Most of these studies were written in response to a new or resurgent disease such as TB, HIV/AIDS, hepatitis B, SARS, MERS, etc. [24,43–49] Generally, these articles all contain a phrase alluding to the possible/ potential infectivity of dental aerosols generated from an infected patient.
To our knowledge, there is no evidence that general dental aerosol exposure has resulted in the infection of dental health care workers or other patients, provided that routine PPE/HVE protocols were in place.
Dental Aerosols and COVID-19
Current evidence points to droplet transmission as the primary vector of infection by SARS-CoV-2. [1,2,5,6,8] Contact transmission plays a minor role. [16] However, some are concerned that the virus could become aerosolized under specific conditions, thereby introducing the possibility of airborne transmission. In dentistry, this concern is particularly relevant because there is a significant percentage of infected people who are either asymptomatic or presymptomatic. [3,50–52] These individuals cannot be identified by routine screening questions or temperature checks. The concern is that treating asymptomatic/presymptomatic patients with AGDPs could endanger the health of the dental health care workers, clerical staff or other patients.
Because COVID-19 is a new disease, we will not have all the facts for quite some time, but we believe there is enough current and historical data to arrive at some reasonable conclusions.
Below are the points on which we have built our commentary:
■ Dental aerosol transmissions have little to no history of infectivity when regular PPE/ HVE is being practiced. [43–49]
■ Six months of patient data have clearly established that COVID-19 is spread primarily by droplet transmission. [1,2,5,6,8]
■ The probability of infection from viral exposure in respiratory diseases is proportional to both dose (viral load) and time (amount of time a susceptible host is exposed to the virus). [4,5]
■ The lowest rate of viral shedding occurs during nasal breathing; [4] during dental procedures, patients generally do not speak, shout or sing. Therefore, the potential viral dose is already quite low. This situation is dramatically different during agitative AGMPs, such as tracheal intubation or bronchoscopy, because they may cause the patient to cough forcefully and release aerosols with a high load of infectious viral droplets. [14]
Contact tracing has established that asymptomatic spreaders can cause cluster infections in various settings: places of worship, cruise ships, family gatherings, nursing homes, restaurants, business conferences, meat processing plants, choir rehearsals, etc. Unquestionably, asymptomatic spreaders have also visited dentists this year. Yet there remain no documented cluster events linked to dental aerosols. We submit that this is because both dose and time are mitigated during traditional dental visits due to PPE, HVE and the brevity of social interactions.
Discussion
The dental regulatory bodies have taken a rightfully cautious approach to limit the spread of SARS-CoV-2, but in doing so, may not have considered historical evidence. Dentists have often (but unknowingly) generated aerosols in patients infected by pathogens. The dental aerosols of 2020 are only marginally changed from those of 2019 and before. Now they may also contain the SARS-CoV-2 virus in addition to the multitudes of previous pathogens. [33,41,45,53] There is no evidence that the viral load of the 2020 dental aerosols is more hazardous than that of those previously encountered.
The use of HVE and routine PPE has protected dentists, staff and patients from cluster infections. If this were not the case, there should be ample evidence to the contrary.
The recent closure of dental offices, in our opinion, was about physical distancing and PPE conservation, with dental aerosols being a much lower priority. It bears noting that during the last pandemic (H1N1, 2009), neither the licensing bodies of Ontario nor Quebec mandated restriction of dental aerosols. Instead, emphasis was placed on preprocedural screening and hand hygiene.
Aerosols from certain medical procedures can be extremely hazardous. Tragic infection and death of health care workers during the SARS and Ebola outbreaks crystalized this awareness. [14] The use of more stringent PPE protocols and other airborne precautions is wholly appropriate for those medical interventions on infectious COVID-19 patients.
In dentistry, unlike medicine, AGDPs have been labeled as hazardous in the absence of evidence. European countries such as Germany and Sweden continued dental practice during the pandemic with only minor upgrades to PPE and other precautions. [54] To our knowledge, there are no incidences of cluster infections linked to dental aerosols in those regions. Medically and dentally generated aerosols are not the same. In a regrettable rush to judgement, these very different interventions have been conflated.
Conclusions
We believe there are two primary concerns in the current regulatory environment:
■ The emphasis on dental aerosol mitigation distracts from the real transmission risk in a dental office — the nonclinical areas. Nonclinical areas are where higher viral doses from sustained speaking (and perhaps even coughing and sneezing) may occur, possibly without masks and certainly without the benefit of high-volume evacuation. Therefore, it is imperative to enforce protocols designed to protect staff and patients in the nonclinical spaces of dental offices, including physical distancing, use of face masks and optimized ventilation.
■ The emphasis on dental aerosol mitigation has created a false impression that visits to the dentist are dangerous. Patients are unquestionably safer in dental offices than in most other social settings. Yet if the public perceives visits to the dentist as a health risk, its dental health will inevitably suffer.
Dentistry has a long history of leading the way in preventing the transmission of communicable, infectious diseases. Consequently, the profession is already well-poised to meet this new challenge. It is the authors’ opinion that minor modifications to already exemplary protocols are what are needed to keep staff and patients safe.
Authors’ note: The original objective of this commentary was to persuade our respective provincial licensing bodies to adopt evidence-based, return-to-work protocols when dental aerosols became the flashpoint of infection control mitigation.
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THE CORRESPONDING AUTHORS, Anthony D. Mair, DDS, MCID, and Paul H. Korne, DDS, MCID, can be reached at drmair@worldofsmiles.com and drpaulkorne@korneortho.com.
