How Often Are Dental Care Workers Exposed to Occupational Characteristics that Put Them at Higher Risk of Exposure and Transmission of COVID-19? A Comparative Analysis

Occupational risk assessment is a method “for estimating health risks from exposure to various levels of a workplace hazard.”¹ As workplace transmission was observed early in the COVID 19 pandemic,² characterizing the role of the workplace in COVID-19 exposure and transmission became an important public health consideration. Agencies, including the World Health Organization,³ the Canadian Centre for Occupational Health and Safety⁴ and the Centers for Disease Control and Prevention (CDC),⁵ emphasize the importance of understanding the risk of exposure to and transmission of COVID-19 associated with varying occupations and implementing workplace safety or mitigation strategies accordingly.

Current evidence indicates that COVID-19 spreads primarily among people who come into close contact (≤ 2 m); transmission is via respiratory droplets generated when an infected person coughs, sneezes or talks.⁵ There is increasing evidence that transmission also occurs through aerosols and less evidence that surface transmission is a major route.⁶ Health care workers are considered to be at a higher risk of exposure to infectious diseases compared with other occupations. Their increased COVID-19 risk results from the provision of treatment, performing “essential” and other routine services for patients with COVID-19 and regular communication with staff and the public in a typical work day.⁷ In Canada, as of 23 July 2020, 19% (21 842) of all COVID-19 cases were among health care workers.⁸ A CDC data from 13 locations in the United States between 1 March and 31 May 2020 showed that health care workers accounted for 6% of adults admitted to hospital with COVID-19.⁹

Dental care workers face unique challenges in mitigating COVID-19 transmission when delivering care as they work in closed environments in close proximity to staff and patients and they conduct aerosol-generating procedures.^10,11 COVID-19 outbreaks have been reported in dental offices in Canada,^12-17 although none included provider-to-patient or patient-to-provider transmission. However, any time an outbreak is reported, it creates panic among dental workers, regulators and associations, and queries related to the nature and extent of the outbreak arise. This raises an important question: what is the risk of occupational exposure to COVID-19 in the dental care workforce compared with other occupations including health care?

Understanding the occupational characteristics that increase the risk of COVID-19 exposure and transmission would support the development of upstream prevention measures for the profession, both at the workplace (e.g., developing workplace policies, training dental staff about infection prevention) and regulatory levels (e.g., paid sick leave, compensation for exposure to hazard during a pandemic).⁷

Methods

Study Design and Sample Population

We conducted a cross-sectional study of employed people aged 15 and over who completed the long-form 2016 Canadian Census of Population. The long-form 2016 Census was completed by 25% of Canadian households and includes detailed information related to demographic, social and economic characteristics.¹⁸

For this study, Statistics Canada provided customized aggregate-level tables of data from the 2016 Canadian census, which included 18 497 145 labour force participants.¹⁸ The 2016 census classified occupation using the hierarchical National Occupational Classification (NOC) 2016 system. We identified occupations using the NOC 2016 4-digit unit group codes, representing the most specific occupational description available (n = 500).

Occupational characteristics of interest were provided by the publicly available Occupational Information Network (O*NET) database (v. 24.3; updated May 2020) developed by the United States Department of Labor/Employment and Training Administration.¹⁹ O*NET is a comprehensive database²⁰ that includes characteristics (e.g., skills, knowledge and abilities) on 974 Standard Occupational Classification (SOC) occupations in the United States.²¹

Linking the 2016 Census to O*NET

Occupational characteristics from O*NET were mapped to occupations in the 2016 census using a publicly available “crosswalk” between occupational classifications systems from the United States (SOC)²¹ and Canada (NOC 2016), described elsewhere.²² This data linkage combines a rich set of population-representative occupation and sociodemographic data in Canada with comprehensive data on workplace indicators that increase risk of exposure to and transmission of COVID-19.

Complete O*NET information was available for 485 of 500 NOC 2016 4-digit occupations.

Occupational Characteristics

O*NET gathers information on occupational indicators through self-reported Likert-scale ratings in questionnaires administered to about 25 people in each SOC occupation.²³ For each indicator, occupation-specific continuous weighted-average intensity scores, ranging from 0 to 100, are calculated.²³

Recently, O*NET indicators have been used to describe occupational characteristics related to COVID-19 risk in the United States and the United Kingdom.^24-27 Based on the existing literature and established COVID-19 risk factors, such as close physical contact, aerosol transmission in indoor settings and accessibility of personal protective equipment (PPE),^10,11,24-28 5 O*NET indicators were selected for this study. For each of these, the specific questions asked and derived continuous weighted-average intensity scores were as follows.

Frequency by which workers are exposed to diseases or infections: Based on the question “How often does this job require exposure to disease/infections?” intensity scores were: 0 = never exposed, 25 = once a year, 50 = once a month, 75 = once a week, 100 = every day.

Physical proximity to other workers in a typical workday: Based on the question “How physically close to other people are you when you perform your current job?” intensity scores were: 0 = do not work near people, 25 = work with others, but not closely, 50 = slightly close, e.g., shared office, 75 = moderately close, e.g., arm’s length, 100 = very close, e.g., near touching.

Indoors, environmentally controlled: Based on the question “How often does this job require working indoors in environmentally controlled conditions?” intensity scores were: 0 = never, 25 = once a year, 50 = once a month, 75 = once a week, 100 = every day.

Wear common protective or safety equipment: Based on the question “How much does this job require wearing common protective or safety equipment?” intensity scores were: 0 = never, 25 = once a year, 50 = once a month, 75 = once a week, 100 = every day.

Wear specialized protective or safety equipment: Based on the question “How much does this job require wearing specialized protective or safety equipment, such as breathing apparatus, safety harness, full protection suits or radiation protection?” intensity scores were: 0 = never, 25 = once a year, 50 = once a month, 75 = once a week, 100 = every day.

In addition, ability to work from home (yes/no) was assessed given its potential for reducing an occupation’s risk of COVID-19 infection transmission. Ability to work from home was derived for SOC occupations from Dingel & Nieman’s white paper,²⁹ by applying cut-offs to ordinal responses for 17 O*NET indicators related to work context and activities.

Dental Occupations

Dental care workers were defined as those working in the following NOC 2016 4-digit occupations: 3113 dentists; 3221 denturists; 3222 dental hygienists and dental therapists; 3223 dental technologists, technicians and laboratory assistants; and 3411 dental assistants. In total, 87 815 individuals worked in dentistry occupations of interest.

Sociodemographic Characteristics

Characteristics for each dentistry NOC 2016 4-digit occupation included median employment income (2015 Canadian dollars [CAD]) and aggregate counts for the total number of workers and across sociodemographic information, including age (15–24, 25–34, 35–44, 45–54, 55–64, 65+ years); sex (male/female); immigrant status (non-immigrant, immigrant, non-permanent residents); household income adequacy quintiles; and visible minority status as proxy for race/ethnicity (Visible minority total, South Asian, East Asian, Black, Southeast Asian, Middle Eastern, Latin American, Visible minority included elsewhere, Multiple visible minorities, Non-visible minority).

Statistical Analysis

Demographic characteristics of the 5 dental occupations (n = 87 815) were assessed descriptively using univariate analysis. For each O*NET indicator, we identified the top 10 occupations (n = 485) based on their respective scores. The O*NET scores of all dental occupations, irrespective of representing the top 10 occupations for the O*NET indicator, were assessed and presented. A cross-tabulation for the 2 most relevant indicators — exposure to infection/disease and physical proximity to others — was conducted to calculate an average score to assess which occupations are at the highest risk of exposure to COVID-19 because of the nature of the occupation.

Results

Occupational exposure and sociodemographic information about the 5 dental occupations are presented in Table 1. In 2016, of the 87 815 Canadians who worked in the 5 dentistry occupations of interest, most identified as dental assistants (n = 34 160), dental hygienists/therapists (n = 26 645) and dentists (n = 18 930). Compared with other dentistry occupations, a higher proportion of workers age ≥ 65 years were found among dentists (10%) and denturists (11%). Women were overrepresented in dental hygienist/therapist (98%) and dental assistant occupations (99%), but underrepresented in the other dentistry occupations, e.g., dentists (39%). The representation of immigrants in dental occupations varied from 16% among dental hygienists/therapists to 52% among dental technologists, technicians and laboratory assistants. Moreover, the proportion of people in dental occupations who were in the lowest household income quintile varied from 4% of dentists to 21% of dental technologists, technicians and laboratory assistants. Based on 2015 figures, dentists had the highest median income of the 5 occupations. Visible minority groups were prominent among dental technologists, technicians and laboratory assistants (37%) as well as dentists (35%). Workers who identified as East Asian, South Asian, Southeast Asian, and Middle Eastern were the most prominent visible minority groups in all dentistry occupations.

None of the 5 dental occupations allow the ability to work from home. Apart from dental technologists, technicians and laboratory assistants, dentistry occupations ranked high for all O*NET indicators except for “Wear specialized protective or safety equipment.” Dental technologists, technicians and laboratory assistants ranked high for 2 indicators: “Wear common protective or safety equipment” and “Indoors, environmentally controlled.”

O*NET scores for the top 10 occupations in terms of risk of exposure to COVID-19 at work for each relevant indicator are presented in Table 2.

Frequency with which workers are exposed to diseases or infections: O*NET scores for the 10 most exposed occupations ranged from 89 to 100; these were all in health care including 4 dental occupations. The only dental occupation not in the top 10 was dental technologists, technicians and laboratory assistants, which scored 72. These scores are interpreted to mean that dental hygienists/therapists, dental assistants, dentists and denturists are all exposed to disease or infection almost every day, whereas dental technologists, technicians and laboratory assistants are exposed at least once a week.

Physical proximity to other workers in a typical workday: Of the top 10 occupations that require working in close physical proximity to others, 8 were in health care, including 4 dental occupations. O*NET scores were 96–100 for the top 10; dental technologists, technicians and laboratory assistants, who were not in the top 10, scored 52. Therefore, dentists, dental hygienists/therapists, dental assistants and denturists nearly touch other individuals during their routine work, and dental technologists, technicians and laboratory assistants work only slightly close to others as they share office space.

Indoors, environmentally controlled: The top 10 occupations who work indoors in a controlled environment include only 2 in health care (pharmacists and chiropractors) and none in a dental occupation. The O*NET scores for these occupations were 99–100; dental occupations scored 97 for dental hygienists/therapists and for dental technologists, technicians and laboratory assistants; 94 for dentists and denturists; and 92 for dental assistants. From the frequency perspective, the O*NET scores indicate that dental occupations work in environmentally controlled indoors almost all (if not all) days.

Wear common protective or safety equipment: Because 21 occupations reported wearing common protective equipment at all times in the workplace, an O*NET score of 100, all have been included in the table. Dental hygienists/therapists and dental assistants were the only 2 dental occupations among them. Dental technologists, technicians and laboratory assistants scored 93, and dentists and denturists both scored 91. These scores indicate that dental technologists, technicians and laboratory assistants, dentists and denturists wear common protective or safety equipment at almost all (if not all) times.

Wear specialized protective or safety equipment: Among the top 10 occupations, the only health care workers who wear specialized protective safety equipment are medical radiation technologists. O*NET scores for the top 10 ranged from 74 to 91. The 5 dental occupations scored 52 for dentists and denturists, 38 for dental assistants, 16 for dental technologists, technicians and laboratory assistants and 14 for dental hygienists/therapists. This means that dentists and denturists wear specialized protective equipment almost once a month, dental assistants a few times in a year and dental technologists, technicians and laboratory assistants and dental hygienists/therapists very rarely.

A bubble plot of all occupations (Figure 1) shows average O*NET scores for the 2 most prominent indicators: exposure to disease or infection and physical proximity to others in a typical workday. Of the 10 occupations with high scores for both indicators (upper right of the graph), all are in the health care sector, and dental hygienists/therapists (100), dental assistants (97.5), dentists (96.5) and denturists (96.5) rank as the top 4.

Discussion and Conclusion

This is the first study to attempt to assess the occupational characteristics that increase risk of exposure and transmission of COVID-19 in the dental care workforce compared with other occupations including health care. Based on O*NET indicators, our study suggests that dental care workers have potentially high occupational risk of such exposure and transmission. In particular, this risk relates to working in close physical proximity to others and a high frequency of exposure to disease or infection. Dental care workers had similar occupational risk of exposure to COVID-19 as some other health care occupations and, on average, higher risk compared with non-health care occupations in Canada.

Although no patient-to-provider or provider-to-patient infection transmission cases have been reported in dental settings in Canada, it is important to acknowledge the potential for underreporting of patient acquisition of COVID-19 infection in dental offices; because symptoms may present only 2–14 days later, patients could have multiple exposures during that time making it difficult to identify specific sources. As such, the high O*NET scores observed among dental care workers for indicators, such as working in close proximity to others and exposure to infection/disease are, in a way, validated through multiple dental office outbreaks reported in the media, which were mainly among staff.^12-17 Overall, our purpose is not to scare the dental community but rather provide data to allow better understanding of workplace characteristics that can increase risk of infection transmission. Attention has focused on how to prevent infection transmission during aerosol generating procedures, but only limited information is available on how staff communicate during off hours or in a staff room. This study will support dental professionals in targeting COVID-19 infection transmission prevention in their offices more comprehensively.

In general, dental care workers do take utmost precautions during dental care delivery to prevent infection. This is evident from our findings that dental workers report using standard protection almost every day to at all times. None of the dental professions was in the top 10 occupations for wearing specialized protective equipment; this is understandable, as specialized protective gear is not required when providing standard care. Currently, specialized protective equipment in dental care occupations is only recommended under special circumstances, for example, when providing care to a patient with a highly infectious disease, such as COVID-19. Throughout the COVID-19 pandemic, the use of non-routine protective equipment, such as N95 respirators, American Society for Testing and Materials level 3 face masks, face shields, safety goggles and protective gowns, has been recommended, based on point-of-care risk assessment, while providing dental care.¹¹ Familiarity with specialized protective equipment may have reduced COVID-19 outbreaks in dental care settings despite the increased occupational risk of exposure to COVID-19.

Throughout the COVID-19 pandemic, the importance of heating, ventilation and air conditioning (HVAC) systems in dental care settings has been boldly underscored. Efficient HVAC systems in a dental operatory are directly linked to the time required to remove aerosol from the area after a procedure. With understanding that dental professionals are at the highest risk of exposure to COVID-19, not only because of conducting aerosol-generating procedures, but also because of other factors identified in this study (i.e., high exposure to disease or infections and working in close proximity to others), it becomes all the more important that they always work in controlled environments. However, results show that dental workers do work in a controlled environment almost every day; thus, inbuilt HVAC systems may not be sufficient to provide the desired indoor environment, especially in older constructions, and supplementary means, such as portable filters, might have to be employed.³⁰

We found that dental technologists, technicians and laboratory assistants do not share the same high level of risk exposure as other dental workers. This may be because technicians work in laboratory settings and, therefore, have no physical contact with patients, have fewer interactions with other staff and are not exposed to infection directly. That said, a systematic review of cross-infection control in dental laboratories highlighted flaws in cross-infection control procedures and disinfection strategies and recommended improved training in disinfection in such settings.³¹

Another factor that is crucial in terms of controlling infection transmission is “presenteeism,” where employees are present at work despite having a sickness that justifies their absence and, as a result, are working under suboptimal conditions, which can be harmful to themselves and others.³² Our results show that no workers in the 5 dental occupations have the ability to work from home. Health care workers, including those in dentistry, are essential skilled workers. The limited availability of substitute workers is exacerbated during COVID-19; therefore, one may expect more presenteeism and, thus, more transmission of infection. This observation calls for cost-effective workplace interventions to reduce dental care worker presenteeism while maintaining a sustainable workforce.³³

Some limitations identified in this work include acknowledgement that risk of exposure to COVID-19 at work measured through O*NET scores is based on typical job characteristics and activities within occupations, not a measure of association based on COVID-19 cases or COVID-19 transmission. Also, workplace exposure indicators were assessed before the COVID-19 pandemic and do not account for changes in workplace policies and/or infection mitigating strategies instituted during the pandemic, e.g., additional environmental controls, specialized personal protective equipment, maintaining physical distance.

In addition, the O*NET database is designed and maintained in the United States. Although, it is a common assumption that job characteristics, such as skills, knowledge and abilities, are generalizable to the Canadian workforce, practices such as frequency of wearing common protective or safety equipment might differ. A similar survey among Canadian dental workers would be useful for making more certain assessments. In addition, the O*NET scores are based on self-reported data, which can be subject to response bias. Misclassification of occupations can also occur for those who are engaged in more than 1 occupation, but we assume that such numbers would be very low.

This analysis has several strengths. It was the first to specifically quantify the intensity of occupational characteristics that potentially increase the risk of exposure and transmission of COVID-19 in dental care workers and objectively compare them with other occupations. These indicators fill an important information gap regarding the lack of COVID-19 data by occupation in Ontario. The study includes the latest census data from Statistics Canada, which provide reliable and comprehensive population-based Canadian information on specific occupations. In terms of assessing occupational risk indicators, O*NET scores were used, which cover working conditions that are derived from survey responses from large, representative samples of workers.

Overall, the results of this study suggest that dental care workers are at a higher risk of exposure to COVID-19 at work than those in other occupations. In addition, the study also identifies opportunities where dental care workers have the potential to improve their work practices to further mitigate the risk of infectious disease transmission. The results of this study will be helpful to administrators and regulators in developing workplace guidance to not only reduce infection transmission but also ensure well-being of the dental care workforce.

THE AUTHORS

	Dr. Singhal is a public health dentist in the health promotion, chronic disease, and injury prevention department, Public Health Ontario; and adjunct professor in the faculty of dentistry, University of Toronto, Toronto.
	Ms. Warren is an epidemiologist in the health promotion, chronic disease and injury prevention department, Public Health Ontario, Toronto.
	Dr. Hobin is a scientist in the health promotion, chronic disease and injury prevention department, Public Health Ontario, Toronto.
	Dr. Smith is a scientist in the health promotion, chronic disease and injury prevention department, Public Health Ontario; and assistant professor at the Dalla Lana School of Public Health, University of Toronto, Toronto.

Corresponding author: Dr. Sonica Singhal, Public Health Dentist, Health Promotion, Chronic Disease, and Injury Prevention Dept., Public Health Ontario, 480 University Avenue, Toronto, ON M5G 1X8. Email: sonica.singhal@mail.utoronto.ca

The authors have no declared financial interests.

This article has been peer reviewed.

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