ENVIRONMENTAL RESEARCH 59, 67-80 (1992)
Medical Surveillance and Screening in the Workplace: Complementary Preventive Strategies MICHAEL GOCHFELD
Division of Occupational Medicine, Environmental and Community Medicine, UMDNJ-Robert Wood Johnson Medical School and Environmental and Occupational Health Sciences Institute, Piscataway, New Jersey 08855 Received May 15, 1992 The terms medical surveillance and medical screening have sometimes been used interchangeably in the occupational medicine literature. Recently attempts have been made to redefine these as mutually exclusive, by nesting surveillance under screening or vice versa, by subsuming both under medical monitoring or periodic examinations, or by eliminating use of the term medical surveillance altogether. In this paper I argue that medical surveillance and medical screening represent discrete concepts and approaches and should be viewed as distinct and complementary secondary preventive components of an occupational health program. Medical surveillance refers to the periodic examination of putatively exposed workers, and is therefore a longitudinal approach. Medical screening refers to the cross-sectional testing or evaluation of a group of workers. Biological monitoring, whether defined narrowly or broadly, focuses on exposure to particular toxicants and should serve as a component of medical surveillance (or of medical screening), not as an independent complement to environmental monitoring. Medical surveillance must function in the context of a comprehensive occupational health program that includes industrial hygiene and education and does not in itself suffice as a comprehensive occupational health program. It is useful to clarify these terms because some of the ethical issues as well as medical controversies over their utility arise from a misunderstanding of what constitutes medical surveillance and how it should be applied. © 1992AcademicPress,Inc.
An increasing variety of medical and other preventive activities are being applied in the workplace to recognize and diminish hazardous exposures and prevent work-related disease. The periodic examination of workers with actual or potential exposure to hazards is a time-honored form of secondary prevention. This strategy has become known as medical surveillance, although some authors prefer the term medical screening (e.g., Halperin et al., 1986a). The recent literature has confused these terms and this paper considers them as discrete and attempts to clarify the confusion by identifying the different usages. A proposed glossary is offered. There is confusion as to what one is looking for in the medical examination of workers: disease, ill-health, impairment, disability, lack of fitness, vulnerability, physiologic or biochemical change, presence of a toxic substance (or metabolite), markers of exposure, or genetic change. All of these can be sought either crosssectionally in a group of workers or longitudinally for individual workers. There is much controversy over the biomedical rationale, ethical basis, and cost effectiveness of periodically examining workers (Ashford et al., 1990). However, 67 0013-9351/92 $5.00 Copyright© 1992by AcademicPress, Inc. All rightsof reproductionin any formreserved.
because the terms medical surveillance, medical screening, medical monitoring, medical supervision (Britain), and periodic examinations have been used sometimes more or less interchangeably (Parkinson and Grennan, 1986; Yodaiken 1986; LaDou 1990), the ethical and efficacy discussions are sometimes confused. For example, ethical shortcomings of certain aspects of employee screening are imputed to surveillance. It is therefore important to distinguish the concepts and establish terminology that has or can achieve widespread acceptance• In this paper I consider the semantic and conceptual distinctions between screening and surveillance as a basis for further discussion of the biomedical, public health, and ethical aspects of medical surveillance, medical screening, and biological monitoring in the workplace• I argue that medical screening and medical surveillance are different, complementary, and useful concepts• The relationships proposed in this paper are, I believe, consistent with widespread usage• The term medical surveillance has gained currency to describe the periodic medical evaluation of workers who have real or suspected exposure to harmful agents (Key et al., 1977; Goldstein and Gochfeld, 1990). Thus in this paper screening refers to a cross-sectional evaluation of a population and surveillance to the periodic examination of individuals on a recurrent basis with longitudinal comparison of data. HISTORICAL CONSIDERATIONS: SCREENING AND SURVEILLANCE Although occupational medical examinations were urged by Rammazini (1713), the term medical surveillance has crept into the literature relatively recently. Johnstone and Miller (1960) did not use screening, surveillance, or monitoring, but mention periodic examinations which should emphasize the importance of education, environmental monitoring, and engineering controls. Hunter (1965) embraced both medical screening and surveillance under the rubric of medical supervision, which he described as "statuatory or voluntary, continual or periodic, permanent or temporary . . . . purely specific o r . . . general." The term medical surveillance did not have widespread currency when I began to perform periodic examinations in 1968. In the pages of the Journal of Occupational Medicine through 1965 I found only one usage. Felton (1964) refers to "clinical surveillance of workers exposed to hazardous materials or radiation. At specific intervals complete or partial physical examination should be conducted. • . ." The earliest use of medical surveillance ! found is by Mayers (1969), who refers to periodic examinations: "this continuity of medical surveillance is combined with an unusual opportunity to c o r r e l a t e . . , medical findings with specific occupational exposures in time-dosage relationships." The term medical surveillance began to take hold in the mid-1970s. A major industrial hygiene manual (NIOSH, 1973) provided a checklist for surveys (Soule, 1973), which identifies two chapters dealing with medical surveillance; however, both of those chapters (e.g., Dinman, 1973) use the term periodic examination with no mention of surveillance or screening. The publication of "Occupational Diseases" (Key et al., 1977) widely established the use of the term medical surveillance, and this term became incorporated into standards and guidelines for federal agencies (Huges et al., 1984). In 1980, OSHA published its medical surveillance recommendations (OSHA, 1980).
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Schilling's text (Schilling, 1981; Bailey, 1981) devotes extensive chapters to medical screening with no mention of surveillance. These chapters emphasize the search for "vulnerable" workers, more than the periodic examination of potentially exposed workers, and his emphasis can be defined as screening for fitness or susceptibility. Goldsmith and Kerr (1982) clearly recognized the difference between medical screening and surveillance. They described a union launching " a full medical screening program for all workers in auto repair shops," involving a one-time cross-sectional study of 2500 workers, which revealed a variety of clinically significant respiratory problems, the findings of which the union used as the basis for improving working conditions. Felton (1983) listed 22 types of, or indications for, occupational medical examinations in which neither the term "screening" nor "surveillance" appears. Elsewhere in the book Felton discussed "environmental surveillance" and used the term medical surveillance to apply to examination of workers exposed to known specific health hazardous substances, a usage which would embrace both surveillance and screening. Rothstein (1984), questioning medical screening on ethical grounds, considered it mainly screening for fitness. Clearly a landmark in the history of occupational health was the NIOSHsponsored Conference on Medical Screening and Biological Monitoring held in 1984 (Halperin et al., 1986a; Mason et al., 1986). This meeting highlighted both methodologic and policy issues. Millar (1986) introduced the issue of screening and used the term monitoring specifically for biological monitoring. Under the rubric of screening, this conference dealt in depth with technical feasibility and ethical desirability of testing workers to determine fitness, exposure, and illness.
SEMANTICS AND CONFUSION: MEDICAL SURVEILLANCE, SCREENING, MONITORING Even in this NIOSH conference, terminology was used with abandon, some authors using screening (Halperin et al., 1986b; Kilburn 1986), others surveillance (Samuels, 1986; Melius, 1986), and others monitoring (Samuels, 1986; Yodaiken, 1986) for approximately the same concept. The confusion continues. For example, paragraph (f) of the OSHA Hazardous Waste Standard (OSHA, 1989) is specifically labeled medical surveillance, but it deals primarily with screening for fitness, devoting little attention to either medical surveillance or medical screening of potentially exposed workers. Rempel's recent book on medical surveillance (Rempel, 1990b) includes papers using screening and surveillance more or less synonymously. For example, Matte et al. (1990) define periodic medical examinations as screening, and Wald and Schneider (1990) clearly describe a one-time medical screening program which they label surveillance. Ashford et al. (1990) reexamined ethical and biomedical bases of what they consider human monitoring. The literature also offers many different combinations among the terms screening, surveillance, and monitoring. For example, monitoring and surveillance are incorporated under screening (Yodaiken, 1986), biological monitoring and screening under surveillance (Halperin and Frazier, 1985), industrial hygiene and bio-
logical monitoring under surveillance (Rempel, 1990a), biological monitoring under screening (Halperin et al., 1986b), screening as a tool of surveillance (Melius, 1986; LaDou 1990), and surveillance as equivalent to biological monitoring of effect (Bernard and Lauwerys, 1986). Halperin et al. (1986b) have employed the term medical screening as a preferred synonym for periodic medical examination. This was to avoid confusion over the term surveillance which Halperin and Frazier (1985) use as an umbrella term (to include screening and biological monitoring). Surveillance is also used in the context of occupational disease surveillance (Stanbury and Rosenman, 1988), the search for cases of occupational disease or sentinel events including injury, indicative of unacceptable workplace exposure or conditions (Rutstein et al., 1983; Baker, 1989). The latter term can be considered a form of epidemiologic surveillance akin to accident surveillance, suicide surveillance, etc., and unlike medical surveillance does not involve evaluation of individuals. There seems little likelihood that medical surveillance would be confused with occupational disease surveillance when the qualifying terms are used. The term screening has multiple and potentially confusing usages as well. Screening usually appears in the context of testing large populations for evidence of a particular disease or condition (Wilson and Junger, 1968). Halperin et al. (1986b) define medical screening "as the application of an examination . . . to apparently healthy persons with the goal of detecting absorption of intoxicants or early pathology . . . . Biological monitoring and testing for susceptibility are subsumed under the general heading of screening." Halperin and Frazier (1985) include both the detection of exposure or of susceptibility under screening. Screening establishes the prevalence of a condition or exposure at the time of the testing, clearly a cross-sectional approach. Working populations can also be screened for non-work-related conditions or as an epidemiologic investigation to see whether there is an increased incidence of certain diseases in certain exposed populations (e.g., colorectal cancer; Hoar et al., 1986). The common denominator is that these are cross-sectional programs. The term monitoring has sometimes been used as a synonym for medical surveillance (Millar, 1986; Yodaiken, 1986), but this use may engender additional confusion with the terms biological monitoring and environmental monitoring, which are also in widespread use. Schilling (1986) discusses the role of medical supervision in Britain, meaning to "monitor those exposed to known or suspected environmental hazards," and thus uses monitoring or supervision as a synonym for medical surveillance. He notes, however, that the medical examination had additional purposes of identifying susceptible individuals, encouraging safe work methods, evaluating control measures, and determining fitness, thus identifying the multiple purposes often embodied in such programs. Ashford (1986) uses the term "human monitoring," emphasizing that a medical monitoring program focuses on workers whereas environmental monitoring focuses on conditions in the workplace. The term biological monitoring, which involves testing individuals for specific substances, their metabolites, or their effects (Baselt, 1980; Levy and Halperin, 1988), may be a separate entity or preferably an intrinsic component of a medical surveillance or screening program. As a further point of confusion,
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environmental toxicologists use the term biological monitoring to mean assessing environmental contamination by analysis of animal or plant tissues as opposed to measurement of abiotic environmental samples (air, soil, water). Bernard and Lauwerys (1986) distinguish three categories of monitoring, creating a slightly different hierarchy: (1) ambient monitoring (= environmental monitoring), (2) biological monitoring of exposure (compared to a biological exposure index), and (3) health surveillance ( = biological monitoring of effect). Screening tends to have a one-time connotation (Deubener et al., 1986). However, Wald and Schneider (1990) apply the term surveillance to a one-time program, which is clearly screening according to the definitions used here. It is, however, true that one can screen certain high-risk groups repeatedly, in which case screening takes on part of the character of medical surveillance. DEFINITIONS AND CONCEPTS
Medical surveillance. The term surveillance is defined as keeping watch over a person, especially one under suspicion. Medical surveillance is primarily the quest for early pathophysiologic changes attributable to workplace exposure. It is designed to detect these changes before ill-health, disease, impairment, or disability occur. Examinations are recurrent, providing longitudinal tracking of workers at significant risk in high-risk jobs or worksites. An important feature of these programs is that they are clearly secondary prevention and are useful as an adjunct to effective primary prevention which for occupational diseases must be accomplished by a combination of process design, engineering controls, industrial hygiene, education, and related procedures. In Britain where medical supervision appears to be a synonym for surveillance, and term medical surveillance is gaining popularity (e.g., Lee and Kloss, 1991). The terms annual or periodic examination are also common synonyms (Dinman, 1973; ILO, 1983); however, in the occupational medicine literature, periodic examination has also been used in a health promotion context (Grimaldi, 1965; Roberts, 1966). As early as the 1950s, some employers were performing such examinations to detect nonoccupational illness (Franco et al., 1961). Medical monitoring. This term seems to have evolved in part to resolve the confusion over screening vs surveillance. There is a tendency to use the term medical monitoring as a more general term, embracing both screening and surveillance, as juxtaposed to environmental monitoring and biological monitoring, or as a synonym for surveillance; hence I find this additional term potentially confusing. Medical screening involves a cross-sectional approach, often nonrecurrent (or at least not at regular intervals), of a group of workers in high-risk situations. The aim is to identify occupational diseases or workplace hazards that have caused or are causing harm. The method may search for clinical disease, or even for subclinical or pathophysiologic changes. Thus the actual clinical and laboratory procedures may be indistinguishable from those employed in medical surveillance. It is the concept that is different. This term should not be used to include "preemployment screening," "drug screening," or "genetic screening." As Halperin and Frazier (1985) state, screening for exposure and for susceptibility is often done as
part of the same examination. It is important to distinguish between these two outcomes and the impact they may have on the individual worker. ATTEMPTS AT CLARIFICATION There have been several attempts to define these terms. Yodaiken (1986) distinguishes surveillance from monitoring as follows: "The object of medical surv e i l l a n c e . . , is to ensure that diseases do not claim new victims." "Monitoring is different. The object of monitoring is not to identify or isolate the first c a s e . . . but to anticipate any disease before it occurs . . . . Screening involves both techniques. We may screen before a diseases occurs . . . or after . . . . " Yodaiken (1986) then goes on to use "traditional surveillance" as the term for detecting "the earliest signs of disease." Atherley et al. (1983) call this biomedical surveillance. Halperin and Frazier (1985) use surveillance broadly as "the collection, assimilation and use of biologic monitoring, medical screening or other health data for developing strategies for the prevention of disease." Rempel (1990a), introducing his recent book (Rempel 1990b), defines medical surveillance even more broadly as "the systematic collection and evaluation of employee health data to identify specific instances of illness or health trends suggesting an adverse effect of workplace exposures, coupled with actions to reduce hazardous workplace exposures," (emphasis mine). Although it is certainly not traditional to include this reduction component as an integral part of surveillance, I concur with the message that performing these tests in the absence of a hazard control/reduction program does not constitute acceptable medical surveillance. This criterion--a committment to control the exposures detected--is so basic that many occupational health professionals do not realize how often medical examinations are performed without this committment. Although I concur with Rempel (1990b) regarding the importance of properly designed surveillance programs, I do not believe that the definition of medical surveillance is enhanced by embracing the control procedures. Typically these are considered the domain of industrial hygiene or are part of a comprehensive occupational health program. The results of medical surveillance may trigger industrial hygiene (environmental monitoring and/or controls), or environmental monitoring may trigger medical surveillance, by identifying a "high-risk" population. The two are inexorably intertwined, but they are not synonymous. Also, although many occupational medicine programs are concerned primarily with medical examinations such as preplacement examinations or surveillance, there are other important but often ignored aspects of occupational medicine, such as disease recognition and establishment of causal relationships (Landrigan and Selikoff, 1992). THE METHODS AND END POINTS Both medical surveillance and medical screening have as a goal the prevention of harm and should aim at the detection of and reduction of exposure. Both may use a variety of clinical and laboratory techniques including questionnaires, physical examination, pulmonary function testing, blood tests, clinical tests (e.g., X rays and electrophysiology), and biological monitoring. Thus the distinction is not
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so much in the rationale or the methodology, but in the conceptual approach: longitudinal versus cross sectional. THE EXPOSURE PATHWAY
The exposure pathway from environmental medium to frank occupational disease offers the opportunity to detect exposure and break the chain at various stages (Lioy, 1990). Obviously the earlier the chain is broken the fewer and less serious the health consequences. Accordingly, the past decade has seen an increasing focus on early detection of exposure through use of biomarkers (National Research Council, 1989), rather than on identification of disease. Indeed Halperin et al. (1986b) and Levy and Halperin (1988) use screening to cover the search both for previously unrecognized disease and for evidence of exposure. Levy and Halperin (1988) specifically and correctly exclude from their discussion of medical screening, activities such as preemployment screening for fitness or susceptibility, screening for genetic traits or conditions that might be construed as predisposing to occupational disease or excessive use of health benefits. BIOLOGICAL MONITORING
Biological monitoring is often an important component of either a medical screening or medical surveillance program. Traditionally biological monitoring or biomonitoring meant the quest for a specific toxic substance or its metabolite in body tissues or fluids (Zielhuis, 1978; Halperin and Frazier, 1985). This can be considered the narrow or sensu stricto definition. An increasing number of investigators (Vainio et al., 1983; ILO, 1983) include under this rubric the questfor markers of exposure (protoporphyrins in lead-exposed workers or DNA adducts in those exposed to carcinogens) and even markers of susceptibility (National Research Council 1989). Critics of biologic monitoring note correctly that some employers use such laboratory tests alone as a way of identifying and removing exposed workers, without reducing exposure. Parkinson and Grennan (1986) emphasize the importance of a traditional medical setting and argue that the laboratory tests mandated by OSHA "should never be performed without a careful, comprehensive history and physical examination, because these tests were never designed as screening tests." Halperin et al. (1986b) clearly separate the "biological monitoring" component from the "screening component," and Ashford (1986) distinguishes biological monitoring from surveillance. Yodaiken (1986) also lists biological monitoring, analagous to environmental monitoring, as a tool for monitoring workplace exposures. The designation of "biological exposure indices" (BEIs) by the American Conference of Governmental Industrial Hygienists (ACGIH, 1991), employs "biological monitoring" as Ashford (1986) uses the term, akin to environmental monitoring, thereby conveying the inappropriate notion that biological monitoring can be construed as primary prevention. Indeed some argue out that biological monitoring has advantages over environmental monitoring by integrating exposure across various media and times (Committee on National Monitoring of Human
Tissues, 1991). However, I consider biological monitoring part of a medical surveillance process and on both biomedical and ethical grounds strongly discourage the use of isolated biological monitoring programs (those relying only on a test without obtaining history or examining the employee and often providing no follow-up information to the employee).
GENETIC MONITORING VERSUS SCREENING Another semantic problem involves genetic monitoring versus screening. Genetic screening searches for an underlying genetic predisposition or so-called "hypersusceptibility") while the term genetic monitoring should be restricted to the quest for acquired alterations in genetic material due to genotoxic exposure. These are very different concepts. Unfortunately the Office of Technology Assessment (1983) document used the term genetic monitoring to mean genetic screening. Genetic monitoring can be performed in either a screening or a surveillance context. The use of specialized genetic/cytological tests to detect exposure to genotoxicants in general or to a specific genotoxicant can be viewed either as part of a surveillance protocol, much like a clinical chemistry battery, or as part of the expanded definition of biological monitoring (Vainio and Sorsa, 1983).
ETHICAL ISSUES Clarification of the terminology is not merely a semantic exercise, because specific components or applications of occupational medical programs have engendered ethical controversy (Atherley et al., 1983; Ashford et al., 1984, 1990; Rothstein, 1984). Rather than tarring the entire process with a broad brush, it is valuable to analyze those components that cause the most concern. Many of the controversies focus on specific screening programs. The desire of many employers to detect in advance and exclude job applicants who have unwelcome preexisting conditions or behaviors may lead to preemployment screening for fitness or susceptibility, or for example, to drug screening, and has led to medical exclusion policies. These screening applications are clearly distinct from the medical screening envisioned by Halperin et al. 1986b) and Levy and Halperin (1988). Indeed, Rothstein (1984) notes broadly and unapprovingly, "The purpose of medical screening and laboratory t e s t i n g . . , is to identify persons who are at risk of disease and those who are not." However, both controllable exposures and individual health status interact in determining the likelihood of developing disease, and the former is clearly something that occupational health specialists want to detect and control. Always challenged on ethical grounds, some screening programs will be in violation of the United States' Americans with Disabilities Act (ADA), implemented in 1992. The screening of an exposed group to detect early evidence of illness and the screening of prospective employees to detect those who may have increased absenteeism, use of health benefits, or perhaps be at risk from exposure are fundamentally different concepts, and the fact that the latter is inappropriate and potentially discriminatory (Rockey et al., 1980) should not obscure the utility of the former.
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Ashford et al. (1984), Atherley et al. (1983), and Rothstein (1984) have discussed the ethical/legal issues in great detail. Particularly onerous to these writers are the genetic screening programs for detecting so-called "hypersusceptible individuals." Identifying suspected high-risk genetic traits has generally proven technically unsatisfactory and unproductive (e.g., glucose-6-phosphate dehydrogenase deficiency; Amoruso et al., 1986). Thus much of the ethical concern voiced over medical screening relates to several common practices that have a weak and controversial scientific as well as ethical basis and have been confused with medical screening for exposure or disease. Abuses or alternative definitions of medical surveillance opens it to criticism as well. Nelson et al. (1983) use the term medical surveillance program to apply to mandatory physical examinations the results of which may jeopardize continued employment. To these authors screening is performed to assure that an industry hires only healthy workers; surveillance is done to recognize and eliminate workers who have become unhealthy. Schilling (1986) includes "identifying susceptible individuals" as part of a "well-designed health surveillance program." Clearly the intended use of a program and its impact on individuals, rather than the nature of the tests themselves, weight heavily on the ethical balance. Under ideal conditions no workplace will jeopardize the health of an employee, yet protection of workers here and now may not be able to wait for sluggish improvement in environmental control procedures. Then medical surveillance fulfills a secondary prevention role of detecting exposed individuals who are at risk of occupational disease. I infer from several sources (Rockey et al., 1980; Goldsmith and Kerr, 1982; Lee and Rom, 1982; Atherley et al., 1983; Ashford et al., 1984) that if the employment, earnings, and seniority of an employee are assured regardless of medical findings, then ethical conflict is avoided. Ethical conflicts, and sometimes legal conflicts, arise when these programs are designed solely to reduce employer cost at the expense of employees. RELATION TO INDUSTRIAL HYGIENE
Renes (1978) identifies the need to link industrial hygiene surveys in the workplace and medical surveys (= screening) of workers. Robinson (1990) clearly articulates the relationship between exposure assessment and medical surveillance and argues that the former should trigger the latter and "not vice versa." However, it appears more common to consider the two interrelated and that if the industrial hygiene component has not been adequate, the results of medical surveillance should indeed trigger additional exposure assessment as well as controls. Baselt (1980) treats biological monitoring as an integral part of industrial hygiene and dates this usage back to Elkins (1954). OTHER ROLES FOR MEDICAL TESTING Medical Surveillance for Community Exposures
The past decade has seen the emergence of medical surveillance applied to community groups exposed to environmental hazards (Center for Technology,
Policy and Industrial Development, 1991). For example, lawyers seek damages to pay for the periodic examination in perpetuity of clients who have been exposed to hazardous wastes. Considering that the utility of such a program depends upon the magnitude of exposure and the underlying prevalence of the disease condition being sought, it is apparent that one must have a good understanding of the community risk before invoking a medical surveillance program. In fact, it would be reasonable to initiate a medical screening to determine the magnitude of exposure and the frequency of effect and to use this information as a basis for determining whether an ongoing medical surveillance program is warranted.
Quality Assurance Often overlooked is the role that the medical encounter may play in quality assurance and worker education. If one accepts that primary preventive strategies are essential for preventing occupational disease, then the medical examination affords the opportunity to evaluate the success of these programs and to pinpoint failures (Halperin et al., 1986b). The education opportunity is " a vital portion of every periodic health examination . . . . the never to be neglected opportunity for the physician to sit down with the individual after completion of the examination and unhurriedly to review all pertinent findings . . . . " (Lee and Rom, 1982). Regrettably this phase is missing from many so-called medical surveillance programs. •
GLOSSARY To clarify the distinctions I see among the available strategies I propose the following definitions. Biological monitoring (sensu stricto): The direct testing for a chemical agent or its metabolite in the body, or in the broader sense (sensu latu) including the measurement of specific biomarkers or specific biochemical or pathophysiologic effects. It should be used only as a component of a medical surveillance program. Environmental monitoring: The use of industrial hygiene methods to evaluate a workplace environment with respect to potential exposures. Genetic monitoring: Testing workers for signs of genetic or chromosomal damage indicative of exposure to genotoxicants; performed in the context of medical surveillance. (Can be considered a special case of biological monitoring of effect.) Genetic screening: Testing for genetic traits that might place certain individuals (so-called "hypersusceptibles") at unusually high risk of occupational disease; performed in the context of preemployment screening. These have been largely discredited on both scientific and ethical grounds. Medical monitoring: A probably confusing term that has been used either as a synonym for medical surveillance or as comprehensive term embracing both medical screening and medical surveillance. Medical screening: The cross-sectional testing of a population for evidence of exposure or early stages of disease. Performed by occupational health professionals on groups of workers. Medical surveillance: The longitudinal evaluation of potentially exposed people for early detection of biochemical or pathophysiologic changes indicative of sig-
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nificant exposure. Performed by occupational health professionals on individual workers or groups. Occupational disease surveillance: The detection and follow up of relatively rare or sentinel occupational diseases as a means of detecting significantly exposed populations. In a broader sense this surveillance program can be established for any occupational disease or exposure. This is epidemiologic surveillance, performed by epidemiologists on population-based data. Periodic testing: Testing or examining workers at some predetermined fixed interval for evidence of disease, pathophysiologic changes, or exposure. Can be a synonym for medical surveillance. Preemployment/preplacement screening: Detection of preexisting disease or exposure, or detection of genetic traits or physical vulnerabilities. Results are often used to establish an individual's "fitness" for a certain job, or to determine that the individual might have an increased risk of developing work-related disease in certain job assignments. Some employers screen for workers who have an increased likelihood of using health benefits, an exclusion that is not illegal in the United States under the Americans with Disabilities Act implemented in 1992. CONCLUSION In conclusion, then, medical screening and medical surveillance appear to represent the cross-sectional and longitudinal components of the medical evaluation of exposure and health of workers or others. This clarification is of substantial importance since one-third of United States workers have some form of periodic health examination (Office of Technology Assessment, 1983). Medical evaluation of workers who face real or potential hazards remains an important part of occupational disease prevention. It is essential that the terms surveillance, screening, and monitoring be used with appropriate modifiers. Although terminology in the literature is confusing, the above definitions do not deviate from common usage among occupational health professionals today (e.g., Kilburn, 1986), and no new terms are proposed. The glossary provides the opportunity to use these labels effectively rather than confusingly. It is useful to juxtapose them in a fashion that clarifies the differences among them. It is appropriate to retain the term medical surveillance where longitudinal surveillance is intended and to use the term medical screening where a cross-sectional quest for risk factors, exposure, or disease is intended (Goldsmith et al., 1986). That both purposes may be subsumed in a common examination need not be a source of confusion. The term surveillance will not be confusing if the appropriate modifiers "medical" or "disease" are used. Although it is a secondary preventive strategy, medical surveillance provides an important mechanism for quality assurance of primary strategies and may serve the function of invoking primary strategies. Although no writers have advocated medical surveillance programs in lieu of primary prevention strategies, de facto they often serve in that capacity, a situation that should be corrected. When either a medical surveillance or medical screening program detects significant abnormalities, this should trigger a variety of preventive strategies such as
industrial hygiene and educational programs. The results of a screening program may trigger and serve as the baseline for medical surveillance (Goldsmith and Kerr, 1982). Similarly abnormal findings on a surveillance examination may trigger screening of a larger group of workers, not currently in the surveillance program. Our continued ability to effectively employ the "medical" strategies is dependent on a close look at rationales, objectives, efficacy, and ethical performance. ACKNOWLEDGMENTS I thank William Halperin for stimulating discussions many years ago which led me to try to explain more clearly my conception of medical screening and surveillance. I also thank Joanna Burger for reading and rereading the manuscript and pointing out when clarity was still an elusive objective. Leonard Goldwater, Jacqueline Messite, and Irving Selikoff graciously helped me try to identify the earliest usage of the term medical surveillance.
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