Dentistry in the COVID-19 Era: Application of Lessons Learnt from the University of Washington Department of Oral & Maxillofacial Surgery
After its first reported case in Wuhan, China in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), quickly led to an international public health crisis.1 The first confirmed case of COVID-19 in the United States was believed to have occurred on January 21, 2020. However, as of April 23, 2020, news reports indicate that undetected community spread may have occurred as early as January 2020.2 By March 11, 2020 the World Health Organization officially declared the coronavirus outbreak a pandemic.3,4
SARS-CoV-2 (SC2) is a primarily airborne transmissible disease (ATD), which spreads from person to person via respiratory droplets.5 Dental health care personnel (DHCP) including hygienists, dentists, and specialty providers, are among the most at risk for exposure to SC2 due to their proximity to the oral cavity and their performance of aerosol-generating procedures (AGP) (e.g. procedures which use ultrasonic scalers, high speed dental handpiece).6,7–9
On March 12, 2020, the Centers for Disease Control and Prevention recommended postponing all non-urgent elective procedures and permitting the use aerosol-generating procedures (AGP) only for urgent or emergent cases.10 By March 16, 2020, the American Dental Association (ADA), in an effort to mitigate the spread of COVID-19, recommended dentists postpone elective procedures and concentrate on emergency dental care to alleviate the burden dental emergencies place on hospital emergency departments.11
The University of Washington Department of Oral and Maxillofacial Surgery (UW OMS) has continued to safely provide urgent and emergent services for its patient population throughout the COVID-19 pandemic based on recommendations from UW Medicine and the CDC for SC2 testing and appropriate personal protective equipment (PPE).12 Additionally, national organizations such as the ADA and the American Association for Oral and Maxillofacial Surgeons (AAOMS) have released guidance for the safe reopening of offices.13–16
This article presents an overview of SARS-CoV-2 (SC2), highlights the evidence behind mitigating exposure in outpatient, private practice dental settings, and provides two potential approaches for PPE utilization: a test-based and an incidence-based strategy.
1. Overview of SARS-CoV-2 (SC2)
The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a species of coronavirus that belongs to a family of enveloped, single-stranded RNA viruses known as coronaviridae.5,10 Bats serve as the main host reservoir for the SARS-related coronaviruses.7,10 There are hundreds of strains of SARS-CoV, but only two strains have made the cross-species jump from bats to humans. These are SARS-CoV-1, which caused the SARS outbreak from 2002-2004 and SARS-CoV-2 , which is the cause of the current COVID-19 pandemic.17
Coronaviruses enter the host cell through binding of the spike (S) protein to a specific cellular receptor, and S protein priming of cellular proteases. It is thought that SC2, similar to SC, enters the host cells via its affinity to the receptor angiotensin converting enzyme 2 (ACE2) on human cells. SC2 then uses the host serine protease TMPRSS2 for spike (S) protein priming, allowing fusion of viral and cellular membranes and subsequent viral entry into the host cell. The binding affinity of the S protein and ACE2 was found to be a major determinant of the SC replication rate and disease severity. ACE2 and other host proteases have been detected in both nasal and bronchial epithelium by immunohistochemistry.18–20
SC2 infections typically spread through respiratory droplets or by direct contact. Actions such as coughing or sneezing can aerosolize SC2 and infect individuals within a six foot radius.21,22 SARS-CoV-2 virus particles have been shown to remain viable on inanimate surfaces and can subsequently infect individuals who come into contact with these surfaces (Figure 1).23 SC2 has also been found in the saliva and feces of affected patients.24,25 The potential for transmission via droplets, fomites, or the fecal-oral route highlights the importance for infection control measures to prevent person-to-person spread, especially in the dental office setting.7,8
Recent reports have shown that since signs and symptoms of COVID-19 may not appear for up to 14 days after infection, widespread asymptomatic spread of the virus is common.22,26 Preliminary data suggests the median incubation period is approximately 5 days (range 2-14).26–29
2. SARS-CoV-2 (SC2) Testing
There are three main types of tests used to detect SC2 (Table 1). For active infections, a real-time polymerase-chain reaction (PCR) swab test is used. This test targets the SC2 nucleic acid structure, or RNA. The other two serologic antibody tests determine if someone has previously been infected by SC2 and has mounted an immunoglobulin IgG or IgM antibody response against the virus. These tests are the enzyme-linked immunosorbent assays (ELISA) and rapid serology antibody tests.30 In general, IgM is the first antibody produced in response to an infection and is typically detected 4-7 days after infection. IgG is produced 7-14 days after infection. Time of detection can vary from weeks to months and even years depending on the type of antigen and individual.31
In principle, the RT-PCR test has 100% analytical sensitivity (true positive rate) in identifying SC2 nucleic acid. This means the test correctly identifies every person who has the disease. Due to sampling error or variation in clinical presentation of the disease (e.g., virus present in the lower, but not upper respiratory tract), RT-PCR tests can result in some false negatives. A 2020 study comparing chest CT and RT-PCR on 51 patients in China found that the chest CT showed a sensitivity of 98%, while RT-PCR showed a sensitivity of 71% from the first throat swab or sputum. On the second RT-PCR swab/sputum sample, 23% of the initial negatives were positive. On the third test 4% were positive, and on the fourth test 2% were positive.32,33 A recent study of 23,126 SC2 tests performed on 20,912 patients from UW and Stanford University revealed that among 626 patients who initially tested negative, repeat testing within 7 days yielded a positive result in 3.5% (4.3% UW, 2.8% Stanford).34
At UW, preoperative testing of asymptomatic urgent or emergent operating room patients has shown an SC2-positive rate of 1.1%. Data from the UW Department of Virology has shown the overall SC2-positive rate to be 7.7%, which reflects greater than 95% of the test orders received by UW from inpatient, outpatient, employee health, and community health settings collected across the state of Washington.35
Even though a test may have high analytical sensitivity and specificity, it may not necessarily have high clinical sensitivity and specificity. On April 17, 2020, the ADA issued a warning to dentists to be wary of new tests because of unreliable sensitivity and specificity.36 On May 14, 2020, the FDA issued an alert for the Abbot ID NOW POC test — which was initially touted as a “gamechanger” for testing — for its rate of false negative results.37 Unfortunately as of this writing, no modality for administration of SC2 testing by dentists is currently available, although the ADA is working on having liability protections extended to dentists who administer tests.36,38,39
Serologic testing does not replace PCR testing for active infections. The importance of these tests is that they allow health care providers to know if an individual may have been unknowingly infected. Reports are now showing that up to a quarter of people may have unknowingly been infected with SC2, as they had mild or no symptoms.40 Hopefully serologic testing will allow researchers and public health experts to understand the community spread of SC2 and identify individuals who may be potentially “protected” from becoming re-infected due to the presence of IgG/M antibodies. However, it is not currently known how long, if at all, IgG/M antibodies protect humans from re-infection.
One study of 140 patients examined the combined sensitivity of PCR and serologic testing targeted at specific SC2 antigen to be 98.6% vs. 51.9% for a single PCR test. During the first 5.5 days, quantitative PCR had a higher positivity rate than serologic testing, whereas serologic testing had a higher positivity rate after 5.5 days of symptoms. This study suggests supplementation of PCR testing with serologic testing may aid diagnosis of COVID-19 in subclinical cases (e.g., when the PCR test is negative, but the patient has symptoms).41 Other studies have shown that most people with SC2 do not start producing antibodies until at least 11 to 12 days after symptom onset.27
These studies demonstrate serologic tests are likely to report false negatives for early infections. In addition, serologic tests may miss infections among immunocompromised individuals who don’t produce antibodies.
3. Personal Protective Equipment (PPE) Stewardship
PPE precautions are subdivided into standard precautions, contact precautions, and aerosol transmissible disease (ATD) precautions. Standard PPE precautions include use of a mask, face shield or goggles, gown, surgical cap, and gloves. ATD precautions include airborne/respirator/contact precautions, negative pressure rooms, powered air purifying respirators (PAPR) or N95, eye shield/goggles, gowns, gloves, surgical caps, and trained observers for donning and doffing. New CDC interim guidance recommends wearing eye protection in addition to facemasks.42
Masks range in level of protection from single-use face masks, to surgical masks, and N95 respirator masks. These vary from Levels 1-3 to N95 based on bacterial filtration effectiveness (BFE), particle filtration effectiveness (PFE), and fluid resistance in accordance with performance standards from the American Society for Testing and Materials (ASTM). A single virion of SC2 averages 0.1 micron in size (compared to respiratory droplets, which average 6 microns). Based on the BFE for 0.1 microns, levels 2-3 and high filtration masks provide ≥ 98% effectiveness (Table 2).
UW OMS data published April 28, 2020 estimated a 3.3-fold increased risk for exposure of SC2 from a symptomatic patient compared to an asymptomatic patient. New data from UW preoperative testing shows the risk of exposure to SC2 to be 2.3 viral exposures per 10,0000 asymptomatic patients.
At UW, PPE utilization is currently based on a patient’s SC2 test results and symptoms, as well as whether or not an AGP will be performed. For asymptomatic, SC2-negative patients tested within the last 72 hours and who are undergoing an AGP, standard precautions are implemented. If the asymptomatic patient is not scheduled to undergo an AGP, then standard precautions also suffice. If the asymptomatic patient is scheduled to undergo an AGP and has not had SC2 testing within 72 hours, the procedure should be performed with ATD precautions.
For symptomatic patients, or patients with unknown SC2 status, ATD precautions are utilized. Outpatient dental offices should not treat a patient who is COVID-19 symptomatic or SC2 positive. If these patients have urgent dental needs, they should be referred to a medical facility for treatment.
4. Office Exposure Mitigation
As testing becomes more ubiquitous, we believe that in order for DHCPs to practice safe dentistry, a test-based strategy will become the new normal until locoregional prevalence of SC2 remains stably low (Figure 2). When locoregional prevalence of SC2 drops, we propose a prevalence-based strategy could be safely implemented. For instance when wearing a level 1 mask the risk of SC2 exposure is estimated to be 15 per 10,000 persons.12 Given this risk, if an area has a low prevalence of new COVID-19 cases, then a DHCP would be relatively protected using a level 2-3 masks when performing AGP on asymptomatic patients. This prevalence-based strategy would avoid unnecessary use of ATD precautions.
We define “low prevalence” as less than 10 new cases per 100,000 residents over a 14-day time period. This mirrors the definition the Washington state governor has used for the four-phase reopening plan, whereby counties cannot advance to the next phase unless they have less than 10 new cases per 100,000 residents over a 14-day span.43 The COVID Tracking Project and Washington Post have provided up-to-date data for every state and their 7-day averages for new cases (Figure 3).30,44 However, one should still refer to their county public health department for local case averages.
As an example of how this prevalence-based strategy can be implemented, prior to July 5, 2020, the Washington state 7-day average of new cases was below 10 per 1000,000 residents. With a low prevalence, high filtration masks (eg, N95) may not be necessary for performing AGP on asymptomatic, SC2-status unknown patients. A level 2-3 mask provides enough filtration efficiency that, when used in combination with the remaining ATD precautions, the DHCP is adequately protected from SC2 exposure (Table 3). A low prevalence of SC2, and potential for viable vaccine against SC2, would essentially render the issue of widespread access to SC2 testing a moot point.
Past high turnover strategies used to maximize chair time will for the foreseeable future need to be reconsidered. In aerosol and droplet form, SC2 has been shown to remain viable for up to 3 hours, with a half-life of 1.1-1.2 hours.23 Due to the viability of aerosolized SC2, a 30-minute down time is recommended after completion of an AGP prior to disinfection of the operatory (Table 4a). No down time is required if no AGP is performed (Table 4b). Disinfection can then proceed per usual protocols.45
The recommended time of 30 minutes is based on the assumed air changes per hour (ACH) in a dental operatory. Air changes per hour is a measure of how many times the air within a defined space is replaced. A review of the literature shows the average dental operatory has an ACH between 10.46 For ACH of 10, the time required for removal of 99% efficiency is 28 minutes. ACH is highly variable based on room size and ventilatory system.46,47
PPE Donning and Doffing
While most providers are meticulous when donning PPE, exposure to the virus is still possible when doffing PPE.
Table 5a and 5b outline the steps for donning and doffing PPE that are followed at UW. We would like to highlight the addition of a trained observer to aid the DHCP in removing PPE in order to limit the potential for contamination and exposure. While doffing does not need to be witnessed, all personnel who use PPE should be trained to ensure they are comfortable in the donning and doffing process.
Historically, dental healthcare professionals have always been a high-risk population for exposure to respiratory illnesses. In the past 40 years, the dental community has encountered numerous diseases and organisms, ranging from hepatitis B (HBV), human immunodeficiency virus (HIV), 2004 severe acute respiratory syndrome (SARS, SC), avian influenza, human papilloma virus, the 2009 H1N1 influenza, and now SARS-CoV-2, the cause of the current global pandemic. In addition, there are numerous other environmental exposures that the DHCP must stay informed about in an around their community.
As each of these diseases presents with varying signs, symptoms, routes of transmission, and virulence, the DHCP must stay up to date with new literature regarding SC2 in order to safely treat patients and reduce the risk of exposure to staff. Unfortunately, until accurate, reliable testing modalities or a viable vaccine are widely available, DHCPs will have to utilize ATD precautions when performing AGP. Patients may be asymptomatic carriers or undergoing the incubation period and can be sources for transmission.
As dental offices reopen, DHCPs should be diligent in the implementation of measures to reduce the risk of SC2 transmission. These include those proposed by the ADA, such as symptom attestation, physical/social distancing, and PPE utilization. This article, based on evidence and lessons learned by decreasing risk of exposure during the early months of the pandemic, emphasizes PPE protocol and proposes a vision for future safe practice of dentistry in our new normal.
Dr. Kanvar Panesar, Jasjit Dillon
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This submission is included in the JADA+ COVID-19 monograph as a Clinical Observation entry and has not been peer reviewed.
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