Identifying Risks of Outbreaks in Work Settings and the Implications for Control Measures
Phase: NA
Conditions: Intention to Get SARS-CoV-2 Vaccination, Intention to Get SARS-CoV-2 Antibody Test
Sponsor: Chinese University of Hong Kong

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Identifying risks of SARS-CoV-2 
outbreaks in work settings and 
the implications for control measures 
 
 

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(i) 
Study design 
This is a 5-year study comprising of a randomized controlled trial (RCT), a longitudinal 
quantitative study, a longitudinal qualitative study and a longitudinal workplace hygiene study 
in 3 selected non-healthcare work settings (i.e., non-office, mobile and office). The RCT will 
be implemented at the earliest stage of the project and completed in the first 2 years to generate 
short-term impact of research and inform policy. The 3 parallel longitudinal studies will be 
commenced in the 1.5th year and completed in the timeline of 4.5th year, and thus they would 
provide both the short-term and long-term impact of the research. The layout of overall study 
design and workflow chart is shown in Figure 1. 
The choice of longitudinally repeated measurement using a mixed method of both quantitative 
and qualitative methods is made for the purpose of exploration of the possible new phenomenon 
of awareness and uptake of vaccination of virus tests over time among Hong Kong workers. 
Results from the longitudinally repeated workplace hygiene studies (e.g., airflow rate/direction, 
change volume of fresh air, etc.) would provide timely evidence on informing and enhancing 
the series of repeated quantitative surveys among workers over time. 
 
(ii) 
Subjects to be included 
Study subjects: In the Part I randomized controlled trial (RCT), 294 eligible workers from 3 non-
healthcare work settings will be recruited, and randomized into intervention group (147 subjects) 
and control group (147 subjects). To be eligible to the Part I RCT, all participants are required to 
be aged 18 or above, who can read Chinese and currently being employed in three non-
healthcare work settings from non-office, mobile, and office work environment in Hong Kong. 
We attempt to follow-up all participants of the RCT for 9 months to observe the effectiveness of 
the intervention on improving the primary outcomes, i.e., attitude to vaccination and SARS-
CoV-2 testing.  
In Part II longitudinal quantitative study, we plan to recruit a total of 1,495 workers who are aged 
18 or above and currently working in non-office, mobile, or office work setting in Hong Kong. 
All eligible study subjects in Part II longitudinal/ prospective cohort study will be recruited in the 
timeline of 1.5th -3.5th year of the project and followed up for 2 years to observe the changes of 
attitude to vaccination and virus testing as well as risk profiles of workers towards outbreaks 
over time.  
 

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In the Part III longitudinal qualitative study, we plan to recruit an overall 26 management staff 
and frontline workers (in a ratio of 1:2) with same inclusion/exclusion criteria as the Part I & II 
study, i.e., aged 18 or above and currently being employed in three non-healthcare work settings 
from non-office, mobile, and office work environment in Hong Kong.  
All above planned number of participants to be enrolled in the baseline of the Part I, II and III 
study have already considered a potential loss-to-follow-up rate of about 40%.  
Settings: The 3 work settings are categorized by types as below according to their job nature and 
working environment: 
(1) Non-office work: Workers normally carry out their jobs with a range of environment in an 
indoor or outdoor working space where close contact with the general public is frequent, and 
thus non-office work settings are considered at a higher risk of COVID-19 than the office 
work settings. Workers in non-office settings mainly include construction, accommodation 
and food service (e.g., hotel, restaurant), art/entertainment and recreation, professional bus 
drivers, outdoor instructor, real estate, wholesale and retail trades, etc.  
(2) Mobile work: Workers who frequently move within or in and out of Hong Kong for 
conducting business that involves closer and more frequent contact with the general public 
than the non-office workers, thus their risks to contracting COVID-19 are regarded to be 
the highest among 3 selected work settings. Workers in mobile work settings mainly 
include taxi drivers, food delivery workers, courier delivery workers, police officer, etc.  
(3) Office work: Workers normally carry out professional duties and administrative work in 
an indoor working space, such as an office or a room. Although the details of the job nature 
depend on the type of business to be involved, office work usually include using computers, 
communicating with others by telephone or fax, keeping records and files, etc. In general, 
office work offers relatively stable working environment where close contact with the 
general public is less frequent, and thus is considered having a low risk of contracting 
COVID-19 in the workplace. Workers in office work setting mainly include clerical 
workers, administrative workers, computer technicians, information and communication 
workers, etc.  
Sample size: We estimated sample size for the Part I – Randomized controlled trial according to 
two independent proportions power analysis. As there is no relevant data of willingness to 
vaccination on our target subjects to guide the sample size calculation regarding an educational 
intervention against COVID-19, we employed a conservative assumption that the intervention 
will make a 20% change for worker’s attitude to vaccination/virus test, sample size for both 
groups/arms will be 124, 130, 124, 109 and 79 for the proportion of willingness to 
vaccination/virus test of 30%, 40%, 50%, 60%, and 70%, respectively, with a 90% G-power. 
Therefore, a minimal 79 pairs subjects are required to achieve the primary objective (RCT) of 
this proposal project; if further assuming a loss-to-follow-up rate of about 40%, then an overall 
222 participants with 111 subjects in the intervention group and 111 subjects in the control group 
are required. However, if given the most conservative sample size estimation with 40% loss-to-

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follow-up rate, a total of 364 subjects with 182 subjects in each arm of RCT (130*1.4) are 
required. Therefore, the overall sample size for RCT could reasonably range from 222 to 364 to 
satisfy the primary research objective of this proposal project. In the proposed RCT, we 
considered taking the mean of the “most-least conservative” sample sizes of 294 [(222+364)/2] 
from G-power as a reasonable sample size with 147 subjects in each arm, and this sample size 
(i.e., 294) has already taken into consideration a potential loss-to-follow-up rate of about 40%.  
We estimated sample size for the Part II – Longitudinal/prospective cohort study (quantitative 
survey) according to the formula for cohort studies. As there is no relevant publication for a 
reference, a conservative estimation is used to calculate the sample size for Part II study. For the 
estimation of the maximum sample size of longitudinally quantitative survey for the Part II 
study, the presumed population proportion is set as 0.5, which means that half of the workers 
have positive attitude to vaccination or willingness of SARS-Cov-2 virus testing in the selected 
work settings. It is estimated that a minimum of 1,068 workers is required for the 
longitudinal/prospective cohort study to accept an absolute sample error of 3.0% at 95% 
confidence level. Currently, there is not enough guideline for choosing an appropriate absolute 
error, and an absolute error of 5% is generally recommended in many studies. So, an absolute 
error of 3.0% employed in the project is more conservative than many other studies for sample 
size estimation. Although the required sample size is getting larger with the increase of 
population size, it will not change much when the population size is larger than 20,000. 
According to the latest statistics of the Census and Statistics Department of Hong Kong, the 
employed persons during 12/2020 - 2/2021 in Hong Kong are about 3.6 million, and therefore, it 
is appropriate to adopt this method of sample size calculation for a population-based cohort study 
in Hong Kong working settings. Assuming a potential loss-to-follow-up rate of about 40%, 1,495 
workers are suggested to be recruited in the baseline survey for the Part II study. 
While there is no established requirement for sample size estimation for the Part III and IV study 
which only involve qualitative approach and workplace hygiene measurement, it usually desires 
a reasonable sample size with representative sample.  We plan to recruit 26 (18*1.4) eligible 
subjects at the baseline from 3 defined work settings to participate in the Part III qualitative study 
and 6 representative workplaces for the Part IV study that are regarded as reasonable. We set the 
sample size according to number of participants/workplaces estimated to reach data saturation. 
 
(iii)Methods 
This project includes FOUR parts – Part I randomized control trial, Part II longitudinal 
quantitative study (i.e., prospective cohort study), Part III longitudinal qualitative study, and 
Part IV longitudinal workplace hygiene study. 
 
 

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(iii.1) Procedure of Part I study 
Part I is a 9-month randomized controlled trial to be conducted with single blinding and 
concealment during Year 1-2 (as shown in Figure 1).  
Study subjects of the RCT: Two hundred ninety four workers from non-office, mobile and 
office work settings will be invited to participate in the RCT. The aim of the RCT is to test the 
hypothesis that a 9-month intervention program improves primarily the attitude towards 
vaccination and COVID-19 testing, with impact on the improving the actual uptake of COVID-
19 testing and risk profile toward outbreaks at workplace.  
Procedures of the RCT: All 294 participants will be randomized to intervention group and 
control group. Intervention group will receive theory-based educational intervention using the 
Theory of Planned Behaviours (TPB) PLUS general health information, while the control group 
will receive only general health information. As this RCT will investigate factors that can 
explain worker’s intention to vaccination and virus testing, the theoretical framework using the 
theory for planned behavior (i.e., TPB) is a proper approach for improving workers’ attitude 
toward SARS-CoV-2 and raise their intention to vaccination and virus testing. The intervention 
will be implemented at the baseline with measurements repeated at the 3rd month, 6th month and 
9th month. The standardized mode of intervention includes face-to-face/online seminar (depends 
on the COVID-19 situation), message via mobile phone, promotion pamphlet, etc.  
Primary outcomes of the RCT include attitude to vaccination and virus testing, and the 
secondary outcomes of the RCT are actual uptakes of virus antibody testing and changes of risk 
profile toward outbreaks in the workplace. 
Key contents of intervention would include: 
• TPB intervention: building positive attitudes towards COVID-19 related preventive 
behaviour (e.g., good compliance with infection control measures, encouraging uptake of 
testing and vaccination), subjective norms (tackling strategies for perceived social pressure 
from others or normative beliefs), and improving perceived behavioural control towards 
risks of outbreaks in workplace. 
• Other necessary information: basic knowledge of SARS-CoV-2, chain of infection, health 
and social consequences of infection, general infection control measures, workplace 
engineering and administrative control measures. 
 
(iii.2) Procedure of Part II study 
Part II study includes longitudinal quantitative study (i.e., prospective cohort study) from the 
timeline of 1.5th – 4.5th year involving an overall 1,495 workers recruited at the baseline survey 
from non-office, mobile and office work settings. At the baseline survey, 1,495 workers from 3 
studied work settings will be invited to respond to a standardized questionnaire on exposure, 

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prevention and attitude towards outbreaks, and willingness to be tested for COVID-19 and 
receiving vaccination. Results obtained from the baseline and follow-up surveys will be 
compared to understand the changes of attitudes, awareness, willingness to vaccination and 
virus test, and workplace risk profile of workers towards prevention and control of COVID-19.  
Cohort enumeration at baseline and follow-up:  
A two-stage sampling method will be employed to recruit 1,495 eligible cohort members at the 
baseline survey for the Part II longitudinal quantitative study (i.e., prospective cohort study) in 
the timeline of 1.5th-2.5th year. In stage one, we plan to invite local workers unions with non-
office, mobile and office work settings through our networks and connections, such as the 
Federation of Hong Kong and Kowloon Labour Unions (FLU). There are more than 150 local 
worker unions under the network of FLU, covering a variety of types of worker unions including 
restaurants, transportation, construction, telephone and communication, etc. In stage two, we 
will then recruit about 1,495 workers from the worker unions who agree to participate in the 
Part II study of our project. However, the baseline recruitment of Part II study subjects will be 
stopped if the required sample size of workers is reached.  
All eligible subjects recruited at the baseline will be invited to participate in the follow-up 
survey in the timeline of 3.5th- 4.5th year to compare the changes of attitude to vaccination and 
virus testing as well as risk profile toward infection control in the workplace through various 
means (e.g., telephone, email, worker unions). Any loss-to-follow-up will be recorded. 
Participants who complete the whole questionnaire of the baseline or follow-up quantitative 
survey will receive 200HKD fast food restaurant / supermarket coupon, and if the participant 
completes both the baseline and follow-up quantitative questionnaire survey, she/he will receive 
a total of $400 fast food restaurant / supermarket coupon as a token of appreciation. 
Questionnaire development: 
A standardized questionnaire is designed to capture each participant’s information on 
knowledge, attitude and awareness towards SARS-Cov-2, exposure prevention behaviour, and 
willingness to vaccination and virus testing, with key items on – 
• General introduction 
• Employment status, industry background and occupation, job nature and tasks, 
demographics 
• Worker’s exposure and prevention profile towards risks of outbreaks, including 
knowledge of engineering and administrative control measures (e.g., proper utility of 
personal protective equipment, social distancing), safety culture, types of occupational 
hazards/hazardous process 
• Attitude and willingness to vaccination and SARS-CoV-2 testing, and barriers 
• Previous work and related exposure behaviour and behaviour intention towards 
prevention of infectious diseases in the workplace 

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(iii.3) Procedure of Part III study 
Part III study includes longitudinal qualitative studies in the timeline of 1.5th – 4.5th year 
involving an overall 26 management and frontline workers recruited at the baseline survey from 
non-office, mobile and office work settings. Part III study aims at understanding the level of 
administrative controls in workplace, awareness of virus testing and vaccination and barriers of 
the selected workplaces over time. At the baseline of longitudinal qualitative study, a total of 
26 management staff and frontline workers (in a ratio of 1:2, and after considering a potential 
loss-to-follow-up rate of about 40%) will be simultaneously invited to participate in in-depth 
interviews using qualitative approach to understand the measures of administrative controls of 
their workplaces using a standardized checklist questionnaire developed according to scientific 
literature and documentation review from international organizations, e.g., OSHA, NIOSH, ILO. 
The developed checklist questionnaire will be used as international benchmark to evaluate level 
of measures of control achieved by the respective work settings. In addition, their barriers and 
challenges in getting COVID-19 vaccination and testing will also be investigated. The value of 
qualitative inquiries is to suffix an in-depth understanding of the reasons of the views they hold, 
and the vaccine decision making that are more complex in real life. It will also be useful to 
capture factors attributable to vaccine rejection, hesitancy or acceptance. The insights generated 
from the qualitative study (e.g., detailed barriers and attitudes) will inform questionnaire design 
in the longitudinal quantitative study and also help to explain the results from other parts of this 
proposed project. 
Recruitment of longitudinal qualitative study and follow-up: At the baseline of longitudinal 
qualitative study, we target a total quota of 26 (18*1.4) management staff and frontline workers 
(in ratio of 1:2) selected from the studied work settings using the same eligible criteria as the 
Part II quantitative surveys, assuming a potential loss-to-follow-up rate of about 40%. In 
general, two workplaces from each of the selected work setting will be invited. The rationale 
of the choice of workplaces is based on their relevance to selected settings, for example:  
• Group (1) Non-office: waiters/waitresses from catering companies, construction workers 
from construction companies   
• Group (2) Mobile: taxi drivers, delivery men, social care workers who pay visit to 
individuals and families to provide social care, and international transport workers, such 
as air crew members, seafarers, and cross-border drivers) 
• Group (3) Office: office assistants, clerks, and officers 
Subjects in Group (1), (2) and (3) will be recruited through Workers’ Union that have access 
to members who are our targeted work settings and occupations. Recruitment will be completed 
when data saturation is reached. 
All eligible subjects recruited at the baseline (1.5th-2.5th) of longitudinal qualitative study will 
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with the Part II longitudinal quantitative study and Part IV longitudinal workplace hygiene 
study. Any loss-to-follow-up will be recorded. 
Interview guide and data collection for longitudinal qualitative study: In addition to a short 
questionnaire enquiring the personal profile of participants, a semi-structured 60-min interview 
guide asking open-ended questions will be developed based on literature reviews and expert 
advice from our multidisciplinary research team. 
A trained Research Assistant with good knowledge of the subject area and qualitative interview 
skills will conduct the interview with written consent obtained in prior. Each will last around 
45-60 minutes, be audio-taped and held at the meeting room of our research centre or Workers’ 
Union, with privacy maintained. Each participant will receive HK$200 fast food restaurant / 
supermarket coupon; and if he/she complete either the baseline or follow-up qualitative 
interview, and if the participant completes both the baseline and follow-up qualitative interview, 
then she/he will receive a total of $400 fast food restaurant / supermarket coupon as a token of 
appreciation. 
 
(iii.4) Procedure of Part IV study 
Part IV includes a longitudinal workplace hygiene study in parallel with the Part II and Part 
III study during the timeline 1.5th – 4.5th, aiming at conducting repeated workplace hygiene 
study and assessment in selected work settings to systematically identify workplace hazards 
and/or hazardous process related to infection, and evaluating the existing control measures 
according to occupational health hazard evaluation.  
The longitudinally repeated workplace hygiene study will focus on different indoor 
microenvironments of overall 18 workplaces from 3 selected work settings in Hong Kong 
industries over 5-year timeline, i.e., 6 workplaces from non-office, 6 workplaces from mobile 
and 6 workplaces from office work setting. Direct contact is one of the important transmission 
pathways for SARS-CoV-2, but how to use ventilation to improve aerosol/droplets transmission 
is our major task. Data collection and timeline of this longitudinal workplace hygiene study will 
follow the workflow chart of Figure 1. We will measure the geometry and thermo-fluid 
boundary conditions in indoor microenvironments. A 3D digital model will be built with several 
heated manikins to simulate different scenarios with different numbers of people/workers in 
indoor. The airflow, turbulence, and temperature distributions will be calculated using the RNG 
k-ε turbulence model. This model has the best overall performance among all Reynolds-
averaged Navier-Stokes (RANS) models for enclosed environments. The transient exhaled 
pathogen transport will be calculated using the Lagrangian tracking method. The Lagrangian 
method calculates the trajectories of individual pathogen-containing particles on the basis of 
Newton’s law. The discrete random walk (DRW) model will be used to calculate the turbulence 
dispersion.  

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With the calculated exhaled pathogen-containing particle (aerosol/droplets) distribution, we can 
predict the “hotspots” (aerosol/droplets) with relatively high pathogen concentrations and 
understand how the exhaled pathogen-containing particles (aerosol/droplets) transport from the 
person to person. The information about these hotspots will be provided to the property 
management team for control strategies (e.g. ventilation control or disinfection “hotspots”). In 
order to reduce the person-to-person transmission in confined area, this project will propose 
several partitioning strategies for blocking aerosol/droplets transmission routes. The proposed 
partitioning strategies will also be assessed using the CFD model. The calculated results will 
reveal whether the intervention strategies are effective or not. 
Findings from the longitudinal hygiene study will provide objective evidence to validate the 
self-report of workers from same work settings and inform management for engineering control 
and workstation modification. 
 
(iii.5) SARS-CoV-2 antibody rapid test 
All participants of the RCT who do not finish COVID-19 vaccination will be invited to take the 
SARS-CoV-2 antibody rapid test four times points during the study to observe their attitudes 
toward antibody tests and their actual updates of the testing and compare the differences 
between the intervention and control group, i.e., at baseline, 3rd month, 6th month and 9th month 
of the RCT. We are also interested in inviting and welcoming those already with complete 
vaccination to participate in the SARS-CoV-2 antibody rapid test to understand their attitudes 
towards antibody testing and actual uptakes, and same primary outcomes between the 
intervention and control arms will be compared. The self-sampling test kit will detect the 
IgG/IgM antibody of SARS-CoV-2 from whole blood with above 90% sensitivity and 
specificity, which is recommended by US FDA. 
 
(iv) 
Data processing & analysis  
For quantitative results, descriptive analysis and Chi-square will be used for baseline data to 
analyse the difference in exposure and prevention, willingness to vaccination/testing and actual 
uptake of tests between comparison groups (e.g., work settings). Paired t-test and covariance 
analysis will be performed to compare the longitudinal changes of scores of each exposure 
prevention behaviour factors, attitude and willingness to vaccination and virus testing over time. 
Structural equation modelling and multivariate regression logistic modelling will be used to 
analyze the structural relationship between measured variables and latent constructs, as well as 
examine the association of exposure profile with willingness to vaccination/testing or uptake 
testing. Effectiveness of intervention will be examined by multivariable linear (for continuous 
nature of outcome) or Cox proportional hazard models (for binary outcome). Loss-to-follow-
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up issue of the RCT. All statistical analyses for longitudinal quantitative and RCT data will be 
conducted by SPSS Version 26 and/or SAS 9.4 (SAS Institute Inc., North Carolina). P-value of 
less than 0.05 is considered statistically significant. 
For qualitative analysis, the tape-recorded individual interviews will be transcribed verbatim 
and thematically analysed using Grounded Theory approach. Data will be horizontally 
compared between participants, and longitudinally analysed, tracking and explaining attitudinal 
and behavioral changes of individuals across time. The qualitative data will be delineated to a 
typology of reasons for (1) accepting, delaying or refusal of COVID-19 vaccine, and (2) factors 
contributing to uptake of COVID-19 testing in the workplace, generated through thematic 
analysis.   
 
(v) 
Ethic issue 
The proposed study will be compliance with the Declaration of Helsinki.  
All participants will provide written informed consent. The consent form describes the study 
objectives, requirements for participation, potential risks and benefits for participants, safeguards 
in place to protect participant confidentiality, the study policy that no results antibody tests 
would be revealed to any third party (such as insurance company or employer), that all data 
(whether questionnaire data or biological data) will be analyzed and reported only in aggregate 
form, the voluntary nature of participation and the freedom to withdraw from the study at any 
time, and mechanisms for contacting designated individuals from the study institutions to ask 
questions and obtain further information about their rights as study participants. 
There are no known medical risks associated with completing a questionnaire at entry into this 
study, and the risk associated with antibody test will be minimal. Study subjects or their families 
may face c of confidentiality regarding their questionnaire or antibody tests. However, due to the 
maintenance of strict confidentiality measures and the policy of this study team that research data 
are not disclosed, any potential psychological and/or social harm that could be associated with 
the release of private information is minimized. In the planned database, all data will be 
identified with a study number, and identifying information is maintained in a separate protected 
database. The analytic datasets and biologic specimens will not include the name of the subject 
(or other personal identifying information), and all analyses and reports will be based on 
aggregate data, so that study subjects cannot be identified.