In Belgium, Periodic Health Screenings (PHS) are obliged by law for several occupations, including safety functions, jobs with heightened vigilance, work that involves physical, biological or chemical agents or tasks that are an ergonomic or mental burden. Scientifically it remains an open question whether these screenings guarantee the prevention of later health problems or problems with functioning at work.

The objective of this study is to compare the cost-effectiveness of PHS with an online health screening tool with selective follow-up. In five Flemish hospitals, the employees eligible for PHS (exempting frequent exposure to ionizing radiation, preparation of cytostatics, or exposure to carcinogens, mutagens, or reprotoxic substances) are randomly assigned to a control group (receiving classical PHS at the occupational physician), or an intervention group (e-tool with selective follow-up by the physician). In the intervention group, 20% of the employees is seen by the occupational physician, based on their responses to the questionnaire. The intervention- and control group complete the questionnaire three times: before the study start (June 2019), in February 2020, and in September 2020. The study ends in March 2021.

The survey is developed as part of the study. On the one hand it contains questions for the cost-effectiveness analysis: health care use, absenteeism and presenteeism, and health literacy. On the other hand, a validated questionnaire is developed based on a systematic review of existing validated and reliable instruments, a Delphi panel of occupational physicians, and a pilot- and field study that test the reliability and validity of the survey (and its referral to the occupational physician). For the latter, the employees' health, occupational risks, work ability, and lifestyle (alcohol abuse, drug abuse, physical activity, and nutrition) are surveyed. Access to the occupational physician remains guaranteed by means of an additional question ("Do you wish to discuss the results of your survey with the occupational physician?") and as spontaneous consultations with the occupational physicians remain possible before, during, and after the trial.

The survey platform Qualtrics is used for data collection. Researchers have no insight in personal data, nor the medical files of employees, and only analyse the coded data from the surveys. Invitations for the survey are sent by the occupational physician. The coded questionnaires are saved on a KU Leuven survey, following the ISO-9001-procedure and the legal data storage period. The employer has no insight in the data. The study is performed by Jonas Steel, supervised by prof. dr. Jeroen Luyten and prof. dr. Lode Godderis, and financed by the Belgian Association for Occupational Physicians, and three external services for prevention and protection at work: IDEWE, Liantis, and Mensura.

In Belgium, Periodic Health Screenings (PHS) are obliged by law for several occupations and allow for early detection of health problems, advice towards risk-free behaviour, timely risk reductions or referrals to other care personnel. This makes them one of the key preventive activities of the occupational physician (OP). However, there are as of yet no strong research indications for the optimal organisation of these occupational health screenings. A recent systematic review of general health screening (not only at the workplace) did not find studies that indicated an effect (e.g. on general mortality, cardiovascular mortality, or cancer mortality), but indicated they could lead to adverse effects such as overtreatment or misplaced reassurance. Reviews in other domains such as vision screening of older drivers, tuberculosis screening of healthcare workers, tomography for lung cancer, of pre-employment investigations frequently found too few high quality studies to draw strong conclusions. There is some evidence for the effectiveness of biometric screening in reducing the number of non-communicable diseases, especially when aimed at higher risk employees or if they are combined with well-designed health programmes. However, it remains an open question whether more focused occupational screenings with risk-selection, as is the case in Belgium and the Netherlands, are beneficial.

This protocol will therefore present a study on annual periodic health screenings (PHS). In this sense, it will contribute to evidence-based decision-making for policy makers, who are currently planning to change the legislation.

A theoretically ideal experiment would compare a group of employees undergoing periodic health screening with a group without an intervention. However, three factors make the formulation of an alternative intervention necessary. Firstly, from an ethical point of view, adequate medical follow-up should be provided for all participants in the study. Secondly, current legislation requires employees to undergo screening for "risky" occupational activities to assess their aptitude for those activities. Thirdly, it is important to provide employers with an alternative form of care or follow-up, since it would not be beneficial (for any party) if employers paid the same fees to the Services for Prevention and Protection at Work (SPPW), but got less care in return. The experiment will therefore compare care-as-usual (periodic health screenings by the OP - the control group) with employees that complete an electronic health survey with selective follow-up (the intervention group). The latter encompasses that the employees' answers on the health screening tool determine whether he/she will be seen by the OP. This allows immediate data collection for the experiment, and at the same time guarantees follow-up of employees with health problems by SPPW.

The survey wants to answer to the demands (of a good PHS) of the International Labour Office by focusing on primary (sometimes secondary) prevention, by taking a risk analysis as a starting point, by allowing for both individual and collective measures, by formulating goals in advance, and because finding problems leads to adequate action. To fulfil these goals, the questionnaire will not only make use of health information (health status, early detection of occupational disease, accidents), but also of other signals that could point towards a higher risk of absence or reduced functioning: absenteeism, presenteeism, health care use, working conditions, job-specific factors, and lifestyle. In addition, the health literacy of personnel is taken into account to assess how well information about health at work (eg coming from the OP) is understood. Briefly summarized, health literacy contains three dimensions: access - how employees are able to seek and obtain health information - "understanding" - the expectations, perceived utility and interpretation of health information - and "behaviour" - the employee's intention to change behaviour as well as his behaviour itself. Finally, it is possible to measure the help-seeking behaviour of employees, to assess their tendency to seek medical care when needed. By incorporating these aspects into the survey and study, we will circumvent the complication that many preventive interventions have to face: health ameliorations and decreases in health care use, absenteeism and presenteeism only occur after several years.

Inclusion Criteria:

• all personnel types that are eligible for periodic health screenings: personnel with safety functions, jobs with heightened vigilance, work that involves physical, biological or chemical agents or tasks that are an ergonomic or mental burden
• working age (18-70 years old)
• able to understand and answer the questionnaire in Dutch

Exclusion Criteria:

• occupational groups that perform especially risky activities (frequent exposure to ionizing radiation, preparation of cytostatics, or exposure to carcinogens, mutagens, or reprotoxic substances)

Due to the sensitive medical nature of the data, no data will be shared with other researchers.

Participants are partially masked: if a participant is invited for a consultation with the occupational physician, they do not know whether this is because they are in the control group, or because they were in the intervention group and selected on the basis of their scores. Participants that do not see the occupational physician can deduce that they are part of the intervention group. Care providers, investigators, and outcomes assessors know to which group an individual pertains as this is required for the intervention.