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.