Study design and participants
The current study was conducted as part of the Collaborative Online Research on the Novel-coronavirus and Work (CORoNaWork) Project. Details of the study protocol have been published elsewhere [13]. Briefly, the CORoNaWork Project was an online cohort study in Japan. We extracted online self-administered questionnaire data from the baseline dataset, collected 22–26 December 2020, for cross-sectional analysis. Panelists who had registered with an online research company and who were currently working full-time were invited to participate in the survey. Health care workers and caregivers were not invited to participate. We selected 33,087 participants using cluster sampling, stratified by sex, region, and job type. We excluded invalid responses, which left data on 27,036 participants for analysis. Invalid responses (n = 6051) were (a) wrong answer to a question intended to identify false responses; (b) short response time (≤ 6 min); (c) low weight (< 30 kg); (d) short height (< 140 cm); and (e) inconsistent answers within a question. When the baseline survey was conducted, the numbers of COVID-19 infections and deaths were much higher than they had been during the first and second epidemic waves in Japan; therefore, Japan was on maximum alert during this third wave. In detail, the number of newly confirmed cases peaked at 0.5 per 100,000 population during the first wave (9 April 2020), 1.2 per 100,000 population in the second wave (30 July 2020), and 6.2 per 100,000 population during the third wave (7 January 2021) [14]. This study was approved by the Ethics Committee of the University of Occupational and Environmental Health, Japan (R2-079).
Outcome
The outcome variable, the downloading of the contact tracing app, was assessed with the question “Have you downloaded COCOA?” The response options were “yes” and “no.”
Explanatory variables
Three variables were used to assess industry and workplace characteristics: type of industry, company size, and occupation. Type of industry followed the Japan Standard Industrial Classification, with industries accounting for less than 3% of the sample categorized as “other” [15]. Company size was classified as < 10, 10–49, 50–999, or ≥ 1000 employees. Each participant reported their occupation as permanent employee, manager, civil servant, dispatched or contract worker, self-employed, or other.
Covariates
Covariates comprised (a) demographic characteristics; (b) health behavior; and (c) risk perception. The demographic variables included sex, age (20–39, 40–49, 50–59, and 60–65 years), marital status (single; divorced or widowed; and married), education (junior high or high school; vocational school or college; and university or graduate school), and annual household income (< 2,000,000, 2,000,000–3,999,999, 4,000,000–7,999,999, and ≥ 8,000,000 JPY). The health behavior variables were smoking (never, past, and current) and alcohol intake (never, occasionally, and regularly). Risk perception was assessed using a single question on having anxiety about contracting COVID-19, with response options of “yes” and “no.”
Data analysis
Univariate and multiple logistic regression analyses were used to evaluate the associations of occupational factors with the downloading of the contact tracing app. We assessed three occupational factors as explanatory variables: type of industry, company size, and occupation. Three models were evaluated. Model 1 was adjusted for sex and age. Model 2 was adjusted for sex, age, marital status, education, annual household income, smoking, alcohol intake, and anxiety about contracting COVID-19. Model 3 was additionally adjusted for other variables, including type of industry and company size. We did not include the occupation variables in Model 3 because of the high correlations between the occupation of civil servant and the public service industry and between self-employed occupation and company size of 1–9 employees. All P values were two-sided, and statistical significance was set at P < 0.05. We used Stata/SE 16.1 (StataCorp, College Station, TX, USA) for all analyses.