In this blog I want to highlight the findings in a paper by Morawaska and Cao discussing the Airborne transmission of SARS-CoV-2: The world should face reality. This is a timely review of the mechanisms of transmission of coronaviruses. The main focus to date has being on direct contact with social distancing and hand washing, surface contamination that can be managed using household bleach and droplet spread managed by cough etiquette and masks. The airborne spread mechanism is not featured in public health messages. Furthermore AGPs (Aerosol Generating Procedures) in dentistry using a turbine with water and compressed air or a surgical handpiece in oral surgery pose a risk as an aerosol is created and airborne transmission is possible. As oral surgeons we are trying to qualify and quantify the risk as particular to AGPs and put in place measures to mitigate risk of infection to patient, dental staff and the patients yet to enter the building.   

A publication I referenced in a previous post on LinkedIn from the New England Journal of Medicine found aerosolised virus remained viable for three hours. The W.H.O. state  in response to that publication that these findings need to be interpreted carefully: “in this experimental study, aerosols were generated using a three-jet Collison nebulizer and fed into a Goldberg drum under controlled laboratory conditions. This is a high-powered machine that does not reflect normal human cough conditions. Further, the finding of COVID-19 virus in aerosol particles up to 3 hours does not reflect a clinical setting in which aerosol-generating procedures are performed – that is, this was an experimentally induced aerosol-generating procedure”. Nonetheless I think its not a huge leap to state that when a patient has a high viral load in the oropharynx, possibly six times higher than SARS in some cases, that there is going to be a viral aerosol with a dental AGP. This is a possible route of transmission and Morawaska and Coa spell out that we need to consider this mode of spread especially in indoor situations generally and I want to highlight in this blog that this includes dental settings.

The initial dose of virus and the amount of virus an individual has at any one time might worsen the severity of COVID 19 disease. Viral load is a measure of the number of viral particles present in an individual. Higher SARS-CoV-2 viral loads might worsen outcomes, and data from China suggests the viral load is higher in patients with more severe disease. The amount of virus exposure at the start of infection – the infectious dose – may increase the severity of the illness and is also linked to a higher viral load. It must be stressed at this moment that the relationship between viral load and infectiousness has not been determined for Covid-19. The worry in the oral surgery setting is the asymptomatic patient presenting for an AGP. As a strategy to prevent the dental team being exposed to a potential huge viral load through AGPs, despite PPE, it maybe useful to consider the merits of testing patients for coronavirus and/or previous coronavirus exposure prior to surgery in the immediate post Covid phase. The issue is will testing kits be readily available with high sensitivity and specificity, demonstrating efficacy with low cost. 

The paper makes a recommendation that increased ventilation rate, using natural ventilation, avoiding air recirculation, avoiding staying in another persons direct airflow, and minimising the number of people sharing the same environment helps reduce aerosol transmission indoors (in a dental setting). The paper goes on to explain we need to change how we think about aerosol transmission and suggests global public health authorities are not up speed on this issue.  

The other issue I want to highlight in my blog is the use of air purification systems in the dental surgery / oral surgery setting at this moment as an adjunct to safe surgery. I will post a few more blogs on this shortly but a pre-op history to exclude at risk patients, a hydrogen peroxide mouthwash, PPE and controlling patient flow in the practice is pointless if you do not address the aerosol or virus in the air that becomes recirculated with movement of people and air currents within the building (dental practice or oral surgery setting). This is the moment air purification becomes topical again in dentistry. There are several  Irish dental distributors marketing air purification systems as suitable….beware…there are significant issues with some products and no data.  

‘This leads onto the next paper relevant to the discussion on transmission routes in Dentistry. I have heard several Irish dentists say there is no evidence of airborne transmission therefore we can dismiss it as we need to get back to work as normal.  I have heard other dentists expressing deep concern and others hysterical at the thought of going back to work. Some science is needed to help advise on protocols at this moment to allay fears. My experience to date is patients are very grateful for emergency oral surgery cover. The Irish public are engaging in essential treatment once they see protocols are in place to manage risk at this moment. The paper by Peng et al titled ‘Transmission routes of 2019-nCoV and controls in dental practice’  published in the International Journal of Science lists the possible mechanisms of spread in the dental setting as contact spread, contaminated surface spread and airborne spread. The risk minimisation strategies include using rubber dam and high speed handpieces with anti-retraction. We are not in a position to quantify and qualify risk with AGPs and routine dentistry for Covid-19 as yet with the information that is available. It is incorrect to say that as there is no evidence, equivocal  evidence maybe, of airborne transmission allowing us to dismiss this as a mechanism of spread. Maybe we need to assume bio-aerosol as a possible mechanism for spread until the science tells us otherwise as per Morawaska and Cao protecting our most vulnerable patients. The other factor to be mindful of when trying to adopt individual dental protocols for getting back to work allowing routine dentistry is that risk is very dependent on were we are at in the disease progression throughout our population. When the curve is going up and the delay phase in is operation there is risk, when we progress into the mitigate phase and eventually the curve comes down there is risk. The timelines for all this to happen needs constantly assessed and communicated so risk assessment can be optimised in dentistry as we then enter the post Covid-19 era. In terms of risk to our patients we know that males, the over 70’s, obese, underlying medical condition and black or Asian patients have a biological vulnerability when infected predisposing to a worse outcome. Another factor is that all our infectious diseases experts have told us that they do not know how this virus is going to behave in our population. It may disappear like SARS, it maybe with us forever like influenza with no vaccine mutating every few years like the 2009 H1N1 epidemic or we may get a vaccine next year at the earliest.

Dentistry is an evidence based speciality and at present we have very little solid science. Evidence based dentistry takes time and with a viral pandemic we don’t have the luxury of time to help make decisions on back to work protocols. For the sake of balance to the above thread I have attached an opinion from ‘The British Association of Private Dentistry’ by Damian McNee, The document is titled ‘Worldwide COVID-19 responses: Looking over the garden fence”. This is a document that really angles towards getting back to work looking at some other countries protocols at this moment. The document gives a summary of many countries dental response to the pandemic and concludes 12/17 countries are allowed to remain open for emergency treatment, 5/8 are undertaking staged dental re-opening and 3/8 are encouraged to consider routine procedures on low risk patients. The U.K. dental response is examined with a final executive summary. In that summary he alleges no evidence of transmission between dental professionals and patients and states the government has closed U.K. dental practices without any scientific evidence supporting their decisions. The paper titled “Coronavirus COVID-19 impacts to dentistry and potential salivary diagnosis” by Sabino-Silva et al states that further studies are needed to investigate the potential diagnostic of Covid-19 in saliva and its impact on transmission of this virus, which is crucial to improve effective strategies for prevention, especially for dentists and healthcare workers providing aerosol generating procedures. It goes on to conclude that saliva can have a pivotal role in the human-to-human transmission, and salivary diagnostics may provide a convient and cost effective point-of -care platform fro COVID-19 infection.

This is the third novel coronavirus in twenty years. SARS had a much higher mortality rate and the number of asymptomatic or mildly symptomatic infections was really quite low hence much easier to do contact tracing and isolation because when you were infected it was really obvious. With Covid 19 it is much harder to locate and track infected people given the lack of symptoms and the transmissibility is higher. The worst outcome is that in twenty years time we get a fourth novel coronavirus that has the transmissibility of Covid-19 and the mortality of SARS/MERS. This possibility needs to be discussed in the future. We need to get as much quality research information as possible from this pandemic to plan for the future and understand the evolution, possible transmission mechanisms and ‘real time’ vaccine solutions should that event ever occur. Now that apocalyptic scenario would really end dental practice for a considerable time. So, as dentists and oral surgeons, lets look on the bright side, we will get back to routine work, its simply a question of when and how-but don’t ignore the facts. Covid is transmissible in a dental surgery and Covid kills, same as HIV, TB and hepatitis- issues that we as a profession have all dealt with competently. Let’s not dismiss the aerosol transmission theory when developing Irish dental ‘get back to work’ protocols just yet because that has the potential, if we get it wrong, to do more harm to public confidence on getting patients back into the surgery. The resultant affect could have a further deleterious effect on the current precarious financial health status for so many dental practices. Back to routine dentistry starts in Ireland on the 18th May. The Irish Dental Council has asked that practitioners check the website nearer the time.