key: cord-0766944-1j2iurh5
authors: Magnusson, K.; Nygard, K. M.; Vold, L.; Telle, K. E.
title: Occupational risk of COVID-19 in the 1st vs 2nd wave of infection
date: 2020-11-03
journal: nan
DOI: 10.1101/2020.10.29.20220426
sha: 6ec3c8cb3d7b6e173004f75e38d80213bad19380
doc_id: 766944
cord_uid: 1j2iurh5

Aim: To study whether employees in occupations that typically imply close contact with other people are at higher risk of SARS-CoV-2 infection (COVID-19) and related hospitalization, for the 1st and 2nd wave of infection in Norway. Methods: In 3 553 407 residents of Norway on January 1st 2020 aged 20-70 (with mean [SD] age 44.1 [14.3] years and 51% men), we studied whether persons in occupations in touch with pupils/students/patients/customers (using Standard Classification of Occupations [ISCO-08 codes]) had a higher risk of 1) COVID-19 and 2) hospitalization with COVID-19, compared to everyone aged 20-70 years using logistic regression adjusted for age, sex and birth country. Results: Nurses, physicians, dentists, physiotherapists, bus/tram and taxi drivers had 1.5-3.5 times the odds of COVID-19 during the 1st wave of infection when compared to everyone in their working age. In the 2nd wave of the epidemic, bartenders, waiters, food service counter attendants, taxi drivers and travel stewards had 1.5-4 times the odds of COVID-19 when compared to everyone in their working age. Teachers had no or only a moderately increased odds of COVID-19. Occupation may be of limited relevance for the odds of severe COVID-19, here studied as hospitalization with the disease. Conclusion: Studying the entire Norwegian population using international standardized codes of occupations, our findings may be of relevance to national and regional authorities in handling the epidemic. Also, our findings provide a knowledge foundation for the more targeted future studies of lockdown and disease control measures.

The coronavirus disease 2019 (COVID-19) emerged in late 2019 in China and has in September 2020 resulted in over 29.000.000 infected and over 900.000 deaths globally [1] . In the Nordic countries, the first cases with confirmed COVID-19 infections probably originated from bars and restaurants in Austria and Italy when Nordic residents visited the countries during winter holidays February 2020 [1] . Later, lockdown restrictions of activities particularly in trade, catering and tourism industries are believed to dramatically having reduced the spread of the virus, whereas the lockdown of schools and pre-schools are assumed to have had a smaller effect [2] [3] [4] [5] . However, to what extent occupational settings implying close contact with customers, patients, children or students contribute to the spread of COVID-19 and its severity is currently unknown.

Only a few studies have been published on the occupational risk of COVID-19, mainly focusing on disease severity or mortality. The first reports of occupational risk of COVID-19 are from Singapore in early February 2020 and showed that 25 locally transmitted cases were employed in tourism and trading [6] . Later British studies reported that essential workers such as personal service occupations and plant and machine operatives had a higher risk of severe COVID-19 than non-essential workers, which are believed to work more from home-office [7] . Also, in England, Wales and Sweden, occupations in sales and retail, transport (Swedish bus/taxi drivers) and catering (chefs) had raised mortality rates of COVID-19, whereas teachers had lower mortality rates [8, 9] .

An overview of the pattern of COVID-19 and accompanying utilization of health care services in persons employed in a wide range of occupations is currently lacking. Improved knowledge of occupational risk would greatly contribute to informing authorities on whether certain activities in these sectors should be "locked down" in attempts to limit the spread of the virus with its severe outcomes. Most European countries including Norway are experiencing or expected to experience two waves of infection [10] , one during spring 2020, and one during fall 2020, which due to the novelty of the virus and restrictions undertaken may be associated with different occupational risks. Thus, for the two periods of infection in Norway and including the entire Norwegian population aged 20-70 years, we aimed to study the occupational risk of COVID-19 and its severity (hospitalizations) for persons employed in health professions, education and teaching, trade, catering, travel, tourism and recreation industries.

We utilized individual-level data from the BEREDT C19 register, which is a newly developed emergency preparedness register aiming to provide rapid knowledge of the spread of the SARS-CoV-2 virus and how spread as well as measures to limit spread affect the population's health, use of health care services and health-related behaviors [11] . The register consists of electronic patient records from all hospitals in Norway (NPR), data from the Norwegian Surveillance System for Communicable Diseases (MSIS), The Norwegian Population Registry and the Employer-and Employee-register, which are merged on the unique personal identification number that is provided every Norwegian resident at birth or upon immigration. Thus, BEREDT C19 and our study include the entire Norwegian population including immigrants. Data are updated daily (except for the Employer-Employee-register, which was updated on August 25 th 2020) and spans the whole of 2020. BEREDT C19 includes results for the first positive polymerase chain reaction (PCR) tests for SARS-CoV-2 of every resident in Norway with dates of testing and diagnosis, legally required to be reported from all laboratories to MSIS. The register also includes date of any hospitalization, with complete diagnostic codes from January 1 st 2020. Occupation is reported in the Employer-Employeeregister with codes as described at Statistics Norway for all residents in Norway [12] . Thus, in the current study, our population included all living Norwegian residents in their working age, here defined as age between 20 and 70 years on January 1 st 2020. Non-residents (like tourists, temporary workers and asylum applicants) were excluded (i.e. all d-numbers). Institutional board review was conducted, and the Ethics Committee of South-East Norway confirmed (June 4th 2020, #153204) that external ethical board review was not required.

Occupation was registered with a 7-digit code in the Employer-and Employee-register according to the Standard Classification of Occupation (STYRK-98) [12] . To allow for international comparisons, we used a convert table to make the classification align with the Standard Classification of Occupations (ISCO-08 using 4-digit codes, i.e. corresponding to the Norwegian STYRK-08)) [12, 13] . We selected common occupations with number of employees ≥ 1000 and number of contracted weekly work hours ≥ 1 for a reference week at the beginning of the pandemic (week 10). The occupations investigated in this study, classified as described in Table 1 , usually imply direct contact with other people. Persons not registered with any of the STYRK-codes in Table 1 were classified as "Everyone in their working age (20-70 years)" and included persons with other occupations (here: unspecified occupation with an assumable low degree of contact with customers, patients, children or students). This category also included persons in the population register who had missing value on employment code for unknown reason (nonemployees, persons on disability pensions, work seekers, freelancers, self-employed and students).

We studied two outcomes: 1) COVID-19, which was defined as either having a confirmed positive polymerase chain reaction (PCR) test for COVID-19, and/or by having ICD-10 diagnostic code U07.1 of confirmed COVID-19, and, 2) Hospitalization with confirmed COVID-19 (≥24 hours) [14] . Test criteria for COVID-19 initially included having severe disease, being in a risk group or being health personnel, later changing to include everyone with symptoms or having been in contact with persons with confirmed COVID-19. Thus, we studied our outcomes for two periods, before and after July 18 th 2020. At this date, the number of newly infected daily cases in Norway had decreased to ~0, and had been stable and low for several weeks in July before slowly rising again in the beginning of August [1] [2] [3] [4] [5] . We will refer to the two periods as the 1 st wave (including February 26 th -July 17 th 2020) and the 2 nd wave (including July 18 th -October 20 th 2020).

First, and for each of the occupation groups, we estimated the total number of confirmed COVID-19 cases per 1000 employed persons for the two waves of infection. Second, we assessed the crude association between the exposure occupation group (i.e. a categorical variable including 23 categories, one for each occupation) and outcome COVID-19 (yes/no) using logistic regression for each of the waves. Third, we assumed age, sex and country of birth may confound the association between occupation and wave-specific COVID-19 outcome, and we adjusted for these covariates in a multivariate logistic regression model. We set "Everyone in their working age (20-70 years)" to be the reference category in all analyses. Finally, we repeated the analyses using hospitalization with COVID-19 as outcome, however due to a low number of hospitalizations for several occupation groups, we did not separate these analyses on the 1 st and 2 nd wave. The statistical software used was STATA MP v.16.

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We studied in total 3 553 407 persons aged 20-70 years living in Norway on January 1 st 2020 with mean (SD) age 44.1 (14. 3) years, consisting of 51% men. Of these, 78.8% had birth country Norway and (24.4%) were nonemployed or not registered with any occupation. By October 20 th 2020, a total of 12 736 (0.3%) had contracted COVID-19, of which 953 (7.5%) were hospitalized with severe COVID-19 disease. The proportions with COVID-19 and related hospitalization per occupation are reported in Table 2 and S-table 2, respectively. We refrain from reporting absolute numbers due to few observations for certain occupations. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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Persons employed as nurses, physicians, dentists, physiotherapists, bus, tram and taxi drivers had ~1.5-3.5 times the odds of confirmed COVID-19 during the first wave of infection when compared to everyone in their working age (Figure 1, S-table 1 ). In contrast, teachers of children and students at any age, child care workers, as well as bartenders, waiters, sales shop assistants, cleaners, fitness instructors, hair dressers, hotel receptionists, travel guides and transport conductors had no increased risk, or even a reduced risk of confirmed COVID-19 when compared to everyone in their working age (Figure 1, S-table 1) . Generally, point estimates were closer to 1 in analyses adjusted for age, sex and country of birth when compared to crude analyses (S-table 1). . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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The pattern of occupational risk of confirmed COVID-19 was different for the 2 nd wave of infection than for the 1 st wave of infection. In the 2 nd wave of infection, bartenders, waiters, food service counter attendants, travel stewards and taxi drivers had ~1.5-4 times the odds of COVID-19 when compared to everyone in their working age (Figure 2, S-table 2) . A range of occupations had no increased odds (OR~1): child care workers, teachers of children and students at any age, fitness instructors, sales shop assistants, hair dressers, bus and tram drivers, hotel receptionists, cleaners and health personnel (nurses, physicians, physiotherapists and dentists) when compared to everyone in their working age (Figure 2, S-table 2) . Again, point estimates were closer to 1 in analyses adjusted for age, sex and country of birth when compared to crude analyses (S-table 1). . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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None of the included occupations had any particularly increased risk of severe COVID-19, indicated by hospitalization, when compared with all infected in their working age (Figure 3 , S-table 2), apart from dentists, who had a ~7 (2-18) times increased odds ratio, and pre-school teachers, child care workers and taxi, bus and tram drivers who had a ~1-2 times increased odds ratio. However, for several occupations, no hospitalizations were observed, confidence intervals were wide and all analyses should be interpreted with care due to the small number of COVID-19 hospitalizations (S-table 2). . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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Studying the entire Norwegian population, we report a different pattern of occupational risk of COVID-19 for the 1 st and the 2 nd wave of infection. Importantly, nurses, physicians, dentists, physiotherapists, bus, tram and taxi drivers had the highest risk of confirmed COVID-19 during the 1 st wave of infection, which shifted to bartenders, waiters, food counter attendants and travel stewards during the 2 nd wave of infection (compared to everyone in their working age). Teachers had no increased risk to only a moderate increased risk of COVID-19. We found indications that occupation may be of limited relevance for the risk of severe COVID-19, here studied as hospitalization with the disease.

We believe this report is the first to show the COVID-19 risks of specific occupations for the entire working population and for everyone diagnosed. Existing reports have considered the associations in smaller populations, have used broad categories of occupations and/or have considered only severe, hospital-confirmed COVID-19 or mortality [6] [7] [8] [9] . Here, we study everyone with a positive polymerase chain reaction (PCR) test for SARS-CoV-2 in Norway in addition to hospital-confirmed COVID-19 as well as hospitalizations with COVID-19. For studying occupations, we use the internationally well-known ISCO-codes with four digits, and apply simple logistic regression models, making analyses easily reproducible and comparable when repeated in other countries or in other study samples.

Considering that workers both may become infected through their occupation but may also spread the virus to their customers, patients or pupils/students, our findings may have implications for pandemic policy. First, our findings give no reason to believe that teachers are at higher risk of infection, yet pre-school and child care workers may be at moderately increased risk of severe disease once it is contracted. In contrast, bartenders, waiters, travel stewards, bus, tram and taxi drivers had a higher risk of infection than other occupation groups in the 1 st and/or 2 nd wave of infection, and they also typically have contact with many different people in their work possibly exposing many people if they are not aware that they are infected. These findings may be of relevance for the future considerations of restrictions and/or the use of face masks in certain occupational settings. Our findings also raise important hypotheses for future research. As an example, although we had few cases and considerable uncertainty in our analyses of hospitalization with COVID-19, our results may indicate that dentists are at a considerably increased risk of severe COVID-19, raising important questions of the relevance of viral load or infectious dose in causing severe disease.

Except for our analyses of hospitalization, we chose to divide our analyses in two periods, the 1 st and 2 nd expected "waves" [10] . However, it is questionable whether Norway at all has experienced a second wave of infection, since the number of newly infected cases has been rising slower during fall 2020 when compared to spring 2020 (reproduction number per October 18 th 2020 = 1.1 (95% CI 0.95-1.14) [5] ). Along this line, an important potential explanation for the differing findings in the 1 st and 2 nd wave may be differences in test criteria in Norway throughout the year, which changed from including only those with severe disease, at risk, and/or health personnel before summer to include everyone with mild symptoms and/or who had been in contact with persons having confirmed COVID-19 after summer. These differences in test criteria may also explain why health personnel were at increased risk during the 1 st wave but not the 2 nd wave. However, it is also possible that health personnel have implemented better infection control measures, resulting in fewer nurses, dentists etc. 1 0 being infected as the pandemic progressed. Future research should further detail the association between type of health/medical occupation and infection risk before and after summer 2020, i.e. distinguish between occupations in specialist and primary care, nursing and elderly homes, etc. (work in progress, BEREDT C19).

Another issue of importance to the interpretation of our findings is that 24% of the working age population could not be categorized using available registry data, i.e. they may be everything from students and freelancers to those unemployed and disability pensioned. As an example, the persons infected during the 2 nd wave of infection were younger and likely consisted of more students when compared to persons infected in the 1 st wave of infection [1] [2] [3] [4] [5] . The students, typically aged 20-25, may more often than those aged ≥ 30, have no occupation, and/or more often have part-time work as bartenders, waiters, food counter attendants, child care workers and sales shop assistant etc., potentially explaining our results. The non-employed might also be on disability pensions, typically due to poor health and potentially at greater risk of severe COVID-19, potentially explaining why our findings indicate limited occupational risk of hospitalization with COVID-19. In total 12% of nonelderly adults in Norway are on disability pensions. Also, the proportions fully or partially retired increases from 0% to ~ 95% between age 60 and age 70 [15] , and they may be exposed to a minimal or considerable occupational risk.

Some important limitations should be mentioned. First, we cannot exclude that other factors than the occupation in question explain infection and hospitalization risks in our study. As an example, persons in full-employment may be at greater risk of COVID-19 than persons in part-time employment. Also, we cannot be sure we have sufficiently adjusted for other risk factors related to e.g. country of birth, residential area, risky behavior and health literacy, which may be of particular relevance to our analyses of hospitalization [5] . Further, it is possible that employees working and living close together in small areas (more typical for big cities) may be infected by each other rather than by the customers/children/patients they meet [16] . Indeed, point estimates and their 95% CI were lowered in adjusted analyses compared to crude analyses, suggesting that occupation and our outcomes are partly explained by sociodemographic factors. Finally, we converted the Norwegian occupation classification STYRK-98 to STYRK-08/ISCO-08 and some of the occupations (0.3%) were lost as they did not convert to the international system [12, 13] . The reference category was calculated using STYRK-98.

In conclusion, we show that nurses, physicians, dentists, physiotherapists, bus, tram and taxi drivers had the highest risk of confirmed COVID-19 during the 1 st wave of infection, which shifted to bartenders, waiters, food counter attendants and travel stewards having the greatest COVID-19 risk during the 2 nd wave of infection. Teachers had no increased risk to only a moderate increased risk of COVID-19. Our findings may be of relevance to increase the understanding of risk and transmission settings for COVID-19 in order to contribute to more targeted measures to decrease transmission of COVID-19 in public settings. 1 1 register. The interpretation and reporting of the data are the sole responsibility of the authors, and no endorsement by the register is intended or should be inferred. We would also like to thank everyone at the Norwegian Institute of Public Health who has been part of the outbreak investigation and response team.

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We would like to thank the Norwegian Directorate of Health, in particular Director for Health Registries Olav Isak Sjøflot and his department, for excellent cooperation in establishing the emergency preparedness register. We would also like to thank Gutorm Høgåsen, Ragnhild Tønnessen and Anja Elsrud Schou Lindman for their invaluable efforts in the work on the . CC-BY-NC-ND 4.0 International license It is made available under a

All authors have completed the ICMJE uniform disclosure form and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

The study was funded by the Norwegian Institute of Public Health. No external funding was received.

The funding sources had no influence on the design or conduct of the study, the collection, management, analysis, or interpretation of the data, the preparation, review, or approval of the manuscript, or the decision to submit the manuscript for publication.