Health surveillance is a public health methodology, which aims to detect undesired health effects in a given population; with the primary aim to eliminate the source of the problem. Its tools range from medical screening tests to follow-up and register analysis. Individuals benefit from screening tests (i.e., early discovery of a disorder that leads to better health outcome), or from the identification of adverse effects caused by the (working) environment. Health screening and surveillance of workers varies substantially between EU Member States and are subject to European and national laws and guidelines.
The distinction between health surveillance, screening, case finding, survey and testing is fundamental in order to fully understand and appreciate the inter-relationship between these concepts and practices.
According to the definition of the International Labour Office (ILO), “Occupational health surveillance is the ongoing systematic collection, analysis, interpretation and dissemination of data for the purpose of prevention". In contrast to surveillance of the working environment, which examines factors in the working environment, workers' health surveillance gathers health-related data of and from workers in order to identify and tackle harmful exposures at work. The combination of the two approaches provides the best result to obtain a more accurate picture of the given occupational safety and health situation. Health surveillance observations may include taking personal medical histories, questionnaires and biomonitoring to detect early occupational diseases. This is the reason that health surveillance may feature both primary and secondary prevention characteristics in occupational health and safety. However, health surveillance should target primary prevention as much as possible: the findings of health surveillance should be used as a source of information for primary prevention measures . Thus, the results should be fed into the continuous risk assessment process of the workplace. Similarly, the exposures to hazards identified during risk assessment should guide the scope and measures of health surveillance and screening activities. Whenever the complete elimination or isolation of a hazard is not possible during the risk assessment and management process, health surveillance of the workers is a valuable tool to monitor workers’ health and identify any possible adverse effect of the existing risk .
Screening is the targeted systematic action designed to identify diseases or pre-clinical conditions in individuals who believe they are healthy but who may in fact be at risk of a specific health impairment, and who could benefit from early treatment (or other intervention) . Screening refers to separate actions at a single time point (i.e. cross-sectional measurement approach) while continuous surveillance is a long term process, which may contain repeated screenings (i.e. prospective measurement approach) .
Case finding, surveys, testing
Case finding aims to find individuals with diseases, and to refer patients to treatment. The emphasis is on the individual level as case finding benefits only the individual. In contrast to case finding, the output of surveys is information on the screened population and does not target individual benefits . Case finding and surveys, when carried out in a systematic way, are two possible forms of health surveillance. In terms of “testing", this word is used in a broad sense. As such, it may be advisable to limit it for the actions when individuals are offered tests in a non-systematic way for the purpose of case finding .
In occupational health surveillance, public health methods are applied in occupational settings. While the European legislation sets the minimum requirements, most Member States have detailed provisions designed to provide advanced protection to workers' health. In fact, the Evaluation of the practical implementation of the EU OSH directives in EU member states revealed that the issue of health surveillance was most often the subject of further detailed national regulation. Addressing ethics in health surveillance activities is crucial while processing medical data. Fundamental practices of occupational health surveillance were compiled by the ILO in 1998 . In 2013, the statements of the Guidelines were reaffirmed .
In the European Union, the legal foundation of the given Member State defines whether health surveillance is statutory, optional or voluntary for the entire working population or for a specific group. European legislation dealt with health surveillance of specific groups of workers as far back as 1959 . Article 14 of the Framework Directive 89/391/EC stipulates that appropriate measures must taken to ensure workers have access to health surveillance appropriate to the health and safety risks incurred at work . With the purpose for the early detection of adverse health effects and the prevention of long-term health risks and risk of chronic diseases, several directives (see Table 1) address the issue of health surveillance within their own scope. These provisions are usually broad and general, instructing the Member States to work out the details in line with their own practice and legislation while taking into consideration the most recent knowledge available to occupational medicine. In addition to granting workers the right to ask for health surveillance, the directives specify that positive cases call for arevision of the risk assessment and the (medical) investigation of workers. In certain cases health surveillance should be also available prior to exposure. In the case of diseases with long latency periods (e.g.,asbestos and other carcinogen exposures) the directives concerned offer the option of continued health surveillance even after exposure ends. Directives affirm data privacy and documentation principles in line with international recommendations. The General Data Protection Regulation (2016/679/EU) provides stringent rules on data protection and privacy that also apply to the health surveillance data.With regard to health data in the workplace due to its sensitive nature, these data should only be processed by health professionals who are bound by the obligation of medical secrecy. Workers have also the right to access their medical files and other health-related information.
Data from ESENER-2 show that 65% of the establishments in the EU arrange regular medical examinations to monitor the health of employees. In large companies medical examinations are more common (89%) than in micro enterprises (58%). A study based on a survey of occupational health experts. found that access to health surveillance is not organised in the same manner throughout the EU. In some countries all workers can access health surveillance while in other countries access is restricted to specific groups such as vulnerable persons, exposure to specific risk factors, etc.
Table 1. Directives with references to health surveillance
|Directive 89/391||The Occupational Safety and Health Framework Directive ||Surveillance appropriate to the OSH risk|
|Directive 2013/35/EU||Electromagnetic fields ||Defers to Directive 89/391|
|Directive 2009/148/EC||Asbestos ||Assessment prior to exposure and at least once every three years for as long as exposure continues|
|Directive 2006/25/EC||Artificial optical radiation ||Defers to Directive 89/391|
|Directive 2004/37/EC||Carcinogens ||Surveillance if appropriate prior to exposure and at regular intervals thereafter.|
|Directive 2003/10/EC||Noise ||Surveillance where assessment identifies a risk. Entitlement where a worker exceeds the upper exposure action values.|
|Directive 2002/44/EC||Vibration ||Surveillance where assessment identifies a risk. Deemed appropriate where an identifiable disease or health effect may be related to the exposure; and the disease or effect may be related to the conditions of work; and where there are tested detection techniques available.|
|Directive 2000/54/EC||Biological agents ||'If appropriate' surveillance prior to exposure and at regular intervals thereafter|
|Council Directive 98/24/EC||Chemical agents ||Appropriate surveillance where assessment identifies a risk. Deemed appropriate where an identifiable disease or health effect may be related to the exposure; and the disease or effect may be related to the conditions of work; and where a low risk technique is available|
|Council Directive 2013/59/Euratom||Ionising radiation ||Prior to employment and at least once every year (category A workers). Nature to depend on type of work. Surveillance may continue after cessation of exposure where a medical practitioner indicates a need.|
|Council Directive 92/104/EEC||Surface and underground mining ||Surveillance prior to assignment to specified duties and at regular intervals thereafter.|
|Council Directive 92/91/EEC||Mineral- extracting industries through drilling ||Surveillance prior to assignment to specified duties and at regular intervals thereafter.|
|Council Directive 91/383/EEC||Fixed- duration / temporary employment ||National legislation can exclude temporary workers from work requiring special medical surveillance or must ensure that they receive the same surveillance as required for permanent workers.|
Source: compilation by the authors
Health surveillance methods
Health surveillance is a topic where measures for public health are combined with occupational health. There are several historical examples where occupational health was completely integrated into public health . This relationship may be reinforced through the holistic philosophy of “social medicine" . Based on their shared background, the methods used are similar or stem from the same root. Most actions include medical examinations or access to medical data: individual and collective health assessments (questionnaires, interviews, functional measurements and diagnostic tests, biomonitoring), recording and notification of occupational injuries, diseases and sentinel events as well as sickness monitoring. Investigations and inspections may also be utilised . Occupational health surveillance is designed to :
- evaluate the effectiveness of control measures;
- detect deviations where interventions have beneficial results to workers’ health;
- prevent work-related ill-health or ill-health progression;
- reinforce safe work practices and of health protection; and
- assess fitness-for-job from the perspective of adapting the work to the worker.
The organisers of health surveillance should carefully choose the specific actions for their programme guided by the criteria of health screening to be discussed later. The measures of health surveillance must not be “perfunctory routine" actions. The tests and methods select must have solid scientific foundations (valid, evidence-based). Furthermore these measures must be intended to improve occupational health and safety conditions, and must be appropriate for that purpose. Whenever possible, the organisers should follow evidence based practices and choose only methods relevant to the situation. The periodic revision and adaption of the programme is crucial .
Medical health checks
In many countries, workers must pass a medical health check at employment, while in other countries this is limited to certain exposures/job titles/sectors . Medical examinations include :
- pre-training health/vocational fitness assessments designed to prevent highly sensitive subjects studying (and eventually entering) a profession hazardous to their health;
- pre-employment checks that (i) aim to prevent highly sensitive individuals getting employed in a work environment hazardous to their health, and (ii) provide baseline values for follow-up activities;
- periodic examinations that identify (i) work-related health impairments / diseases or (ii) changes in general health that may have consequences also involving the whole workplace;
- termination examination designed to detect any long-term work-related health impairment at the time the employee leaves the company;
- post-employment, follow-up examinations that continue to monitor the workers after exposure ends to enable early diagnosis of occupational diseases with long latency periods (e.g., occupational cancers)
The examinations should be tailored to the specific conditions and requirements of the job/occupation/workplace concerned. In addition to protecting workers’ health, medical examinations must serve prevention as a whole, including social protection (i.e. promoting access to work and compensation, adaption of work to the worker). Workers should have the opportunity to require a medical examination in suspected cases of work-related ill-health, (i.e. occupational disease, or general disease aggravated by work) . The first three examinations listed above can also be used to identify workers that would pose a risk to their own or others’ life/health/security in certain jobs because of their health conditions. These objectives are not within the original scope of occupational health surveillance . The efficacy of pre-employment examinations in disease and injury prevention has been criticised, with claims that there is no evidence available that would show any positive effect on the prevention of accidents at work or occupational diseases .
Biological tests, including biomonitoring
The vast potential of medical laboratory testing is available for health surveillance. However, special care needs to be taken when choosing tests. Several medical tests are not intended for screening. For example, the so-called ‘tumour marker blood tests’ do not have enough validity and predictive value to be used for screening. Instead, they are capable exclusively for the monitoring of patients with certain confirmed malignant diseases during treatment and afterwards. For instance, when there is carcinogen exposure at the workplace, cytogenetic surveillance may be applicable. Note, this biological monitoring methodology is applicable only to estimate the risk on a population level.Biological monitoring is appropriate for the earliest detection of overexposure and well-established methodologies are available for their use in health surveillance . Biomonitors have the advantage over environmental monitoring in that they take into account all sources of exposure (e.g.,air, dermal, ingestion) and the characteristics of the individual’s response. An ideal biomonitor is very sensitive to the exposure with no or little confounder by other exposures or health conditions, characterised by an understood pathway (metabolism and kinetics) within the human body. It should also detect exposure far before clinical symptoms appear (in a reversible phase), it should not require invasive sampling or precise timing, and should be easy to transport and analyse .
Registries and notifications
Analysis of occupational diseases, injuries and occupational sentinel health events and sickness absence data may be used in health surveillance. Co-operation with the worker’s general practitioner may be advantageous, but the consent of the worker is necessary.
Occupational Sentinel Health Event (SHE – Occupational)
The concept of SHE (Occupational) is that certain work-related diseases, health impairments, or untimely deaths can be used as indicators. On one hand, these cases may initiate scientific research in the sector concerned. On the other hand, however, these events may be warning signals highlighting that occupational safety and health at the given workplace is insufficient and intervention (substitution, engineering control, personal protection, or medical care) is necessary. An elaborate EU-OSHA report provides an overview of alert and sentinel systems in the EU. Alert and sentinel systems are described as 'an umbrella term for timely surveillance systems that collect information on diseases to initiate health interventions and prevention. These early warning systems should not be confused with systems that screen for early health effects of already known diseases (in other words detection of early health effects, which is a specific form of health surveillance)'. The aim of such systems is to detect work-related problems at an early stage in order to prevent work-related health problems. Individual sentinel signals rely on the identification of individual cases (diseases) that might be work-related. Such system goes through successive stages: an occupational health physician (or other expert reports the case, next, a team of experts assesses if the case is work-related, followed by additional research to strengthen the signal and finally, depending on the outcomes, information and preventive actions. An example of such an individual sentinel system is SIGNAAL (BE, NL) https://www.signaal.info. Population-based sentinel signals identify groups of workers (e.g. economic sector, job) with an increased incidence of a work-related disease. These systems rely on data mining techniques and large databases. Systems that are suitable for identifying these signals are non-compensation-related systems characterised by a wide coverage and a large database that can be used for collecting statistics and data mining. More information and examples can be found in the EU-OSHA report https://osha.europa.eu/en/publications/alert-and-sentinel-approaches-identification-work-related-diseases-eu/view.
Health surveillance programmes
As discussed earlier, European directives set the guidelines for and national legislations can specify the content and the methodology of health surveillance. Health surveillance programmes should meet four criteria: need, relevance, scientific validity and effectiveness. A workplace programme needs to be tailored to the specific circumstances of the enterprise. There are four key players in health surveillance: the competent authority, employers, employees and occupational health professionals. Their cooperation is essential for a well-functioning occupational health surveillance system. Settings can range from workplaces and company occupational health services to municipality health centres or contracted specialists. The preferred settings for health surveillance are occupational health services organised in accordance with the ILO's Occupational Health Services Convention, 1985 (No. 161) and Recommendation (No. 171) . Bound by professional ethical guidance, health professionals are authorised to handle medical data. Furthermore, occupational health services employ professionals with relevant medical studies and experience with work-related health issues . Some directives permit that occupational health surveillance is provided as part of a national health system. National guidelines are usually available for the surveillance of workers exposed to traditional risk factors. The surveillance of those working among new risks, like nanomaterials, is more challenging due to lack of knowledge on pathology and of approved tests; these criteria are mentioned among the principles of screening .
Ethics in occupational health surveillance
Every health surveillance action must be transparent and carried out by professionally independent and impartial health professionals . It must ensure workers' privacy and the confidentiality of individual health information. Medical health checks must not be used for discrimination. The actions are justifiable if they are absolutely necessary (substantial improvement of prevention can be expected) and they pay close attention to the dignity of workers. Although workers cannot be forced to participate in medical examinations. However denial may prevent their employment in cases when participation is a condition of employment. Regulations on this issue vary significantly among Member States.
Workers must have access to their own health records as required. The employer or the workers’ representatives can be informed only by collated anonymised data, unless provided by the specific worker’s prior consent. The communication of results to the worker should be clear and balanced, with advice offered for the protection of the worker’s health .
Screening is widely used in occupational health surveillance. Screening is also often offered within workplace health promotion programmes. Some knowledge on the basics of screening is necessary to understand its relation to and use in health surveillance. Screening tests are not meant to be diagnostic. Instead, their purpose is to separate individuals into groups with either low or high probability to develop a certain disease.
Criteria of health screening
The WHO set the principles of screening for public health (including “industrial health examination") in 1968. These “Wilson and Jungner principles of early disease detection" are still valid today:
- The condition sought should be an important health problem (on the individual and/or population level).
- There should be an accepted treatment for patients with the recognised disease.
- Facilities for diagnosis and treatment should be available.
- There should be a recognisable latent or early symptomatic stage (detectable pre-clinical phase).
- There should be a suitable test or examination.
- The test should be acceptable to the population.
- The natural history of the condition, including development from latent to declared disease, should be adequately understood.
- There should be an agreed policy on whom to treat as patients.
- The cost of case-finding (including diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole.
- Case-finding should be a continuing process and not a "one off" project.
More specific prerequisites have been developed by current national recommendations, such as that evidence is required demonstrating treatment is better than non-treatment; the distribution of test values in the target population is known; there is an agreed policy on cut-off values; and on the further diagnostic tests. A suitable test should be simple, safe, precise and validated . These criteria can be applied to screening in occupational health and safety as well.
Validity of screening
We need some parameters to quantify the performance of a specific screening method. These parameters are expected to indicate how “good" the given method is. Based on such figures comparisons and, subsequently decisions can be made. Validity summarises the overall success of the test process, it is the confirmation rate of the test results (both positive and negative) by an agreed diagnostic method.
Validity of the test
Sensitivity and specificity are the two core indicators of validity. Sensitivity is the ratio of true positive cases identified by the test. Specificity is the ratio of the true negative cases identified. While sensitivity is the basic measure of success, specificity is a basic measure of the disadvantages concerning the test. In both ratios, the higher the value the better the test. However, the two indicators are inversely related. If a cut-off point is made stricter to elevate sensitivity it will identify more cases (more true positives but also more false negatives). This growth in the number of false negative cases will lessen the rate of true negatives. Thus, the consequent drop in specificity is the cost of increasing of sensitivity. Predictive values show the ratio of true positive or negative cases. Positive predictive value tells how many true cases are among the test-positives, in other words: how certain the test/measure is in that someone with a positive test result is really affected by the condition. The negative predictive value is the ratio of true negative cases among the test negatives, in other words: how certain the test/measure is in that someone with a negative test is really free from the disease. Predictive values depend on the validity of the test, and also on the prevalence of the disease in the observed population. The latter means that if the condition is common in the target population then it is more likely to identify more true positive cases (higher positive predictive value), but the ratio of false negatives will be also higher (lower negative predictive value).
Success of screening
In a target population a successful screening programme must be able to:
- identify the disease at an early stage (equals “programme validity"); and
- improve the average prognosis of the disease.
In addition to the above characteristics of the test, several circumstances must be taken into consideration that may have a significant effect on the final outcome of a screening programme. Attendance is important as consideration should be given to the participation rate and whether those most at risk would attend. The screening interval should be reasonably short enough to spot cases that develop in between two screenings. The overall success of lowering the burden of disease depends on the willingness of test positive cases to attend the confirmation diagnostics, and on their proper and timely treatment. In selective screening the individuals with the highest risk are screened. In such risk groups the chance of true positive results is higher. Moreover, the positive predictive value of the test is higher, which is an important success factor. Multiple/multiphasic screening is the "the application of two or more screening tests in combination to large groups of people" (pg. 45). This may save time and enhance coverage thus contribute to the success of the programme. However, all the tests in the combination must be relevant for the target population.
While a screening programme must always be adapted to the actual circumstances, some common success factors include:
- identified target population
- identifiable individuals
- measures that guarantee high coverage and attendance
- available facilities for the programme
- quality control
- facilities for confirmation diagnostics, treatment and follow-up
- managed pathways of referral and information
- use of appropriate and quality controlled epidemiology data.
Adverse effects of screening
Several medical treatments, both in Europe and in other parts of the world, have been in the spotlight as to whether or not they have a positive impact. Theoretically, occupational medical surveillance and screening practices can be also the subject of such concerns. The importance of delivering these services and measures on a firm scientific evidence-based ground is exemplified by the American College of Occupational and Environmental Medicine (ACOEM) joining the Choosing Wisely initiative of the United States . This initiative fosters a dialogue between patients and physicians to choose evidence-based, non-duplicative, harm-free and only necessary tests during the treatment. It generates debates over “routine" procedures and tests that may lack these features. Stakeholders must bear in mind that screening can be harmful as they can:
- increase risks of further diagnostics, anxiety and costs of false positive cases;
- provide a false sense of security in false negative cases.
These harmful effects have special importance, because these programmes are offered to individuals who believe they are healthy. For such healthy, complaint-free individuals accepting any harm caused can be very difficult; unlike in curative medicine where the patient with a disease/complaint seeks for help and asks for the intervention, which has a certain degree of risk that the patient accepts.
Screening in workplace health promotion
The idea of screening tests being offered at workplaces for the detection of non work-related diseases is not new. With the rise of non-communicable diseases in industrialised countries the focus of prevention shifted towards general diseases like diabetes mellitus, hypertension, coronary heart disease and chronic bronchitis. Population studies have confirmed that early detection of several non-communicable diseases can produce health and economic benefits. Health promotion for the working population has several advantages . Firstly, the working population is younger than those in retirement. At a younger age health abnormalities are usually not that developed and these early disorders may respond better to treatment or may be reversible, compared to full fledged diseases. Secondly, the working population is well-accessible via the workplace. Thus workplaces are ideal for workplace health promotion, including screening. However, any such action must respect the principles of health screening. Furthermore, the stakeholders must realise that these measures do not replace occupational health surveillance; they are complementary to each other. Attendance of workplace health promotion screening must be completely voluntary and the resulting health data of individuals are subject to privacy.
Occupational health surveillance is the systematic and continuous monitoring of workers’ health in relation to workplace hazards. The overall goal of health surveillance measures is the continuous improvement of safety and health at workplaces and the protection of workers’ health. The positive results of a health surveillance action can also reassure employees and employers concerning their good practices and health and safety culture. Most health surveillance measures are related to personal health data thus data privacy is of utmost importance. In an ideal situation health surveillance measures are organised by occupational health services. National regulations may contain various requirements to fulfil. Any further activity or service (including workplace health promotion) should have a firm scientific basis, must be agreed upon by social partners and should not be consumer-driven. Proper documentation of health surveillance findings provides a safe basis for employers, employees and occupational safety and health specialists in case of legal claims. Such data can also provide a starting point for scientific research.
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