Work-Relatedness

Abstract

INTRODUCTION Physicians are frequently requested to determine whether putative risk factors—occupational or nonoccupational—caused an injury, disease, or disorder; therefore, a valid and reproducible method to analyze the available clinical information, epidemiological evidence, and exposure data should be used to determine causation. This determination is not only important to evaluate an individual patient, but also other workers who may be similarly exposed. Interventions to improve the safety of workers by mitigating or eliminating these exposures should be evidence-based. Determination of work-relatedness can determine financial compensation, including past and future expenses of treatment, vocational rehabilitation, permanent or partial disability benefits, and diminution of earning capacity.1,2 Because the legal standard for determining work-relatedness may vary jurisdictionally, physicians must be aware of the relevant definition of work-relatedness. Although the legal basis for work-relatedness often differs between jurisdictions, the scientific method for determination of causation or apportionment among occupational, nonoccupational, and personal risk factors remains consistent. The distinction between establishing medical causation and legal causation is critical: Medical causation is determined by scientific criteria establishing a causal association between an injury, illness, disease, or disorder and known risk factor(s). Legal causation is determined by criteria established by legal authority. These criteria vary among jurisdictions. Although the crux of this guideline is the determination of medical causation, a few examples of legal causation follow. Pursuant to the common law of negligence, proximate cause (legal cause) is the primary cause, or that which in a natural and continuous sequence, uninterrupted by any intervening cause, produces injury, and without which the result would not have occurred. An injury is proximately caused whenever a defendant's negligence actually caused the injury, and the injury was either the direct consequence or a reasonably foreseeable consequence of that negligence. Statutory schemes may redefine the conventional common law definition of legal cause. Under the Federal Employers Liability Act, which applies to interstate railroad carriers, the plaintiff has the burden of proving that the railroad's negligence was the proximate cause, in whole or in part, of plaintiff's injury. Courts have construed this statutory language to require mere proof that a railroad's negligence proximately caused a worker's injury, even to the slightest degree. This same lenient standard applies to actions prosecuted under the Merchant Marine Act of 1920 (commonly referred to as the “Jones Act”). Pursuant to worker's compensation statutes, state legislatures may create presumptions concerning work-relatedness that establish rights and liabilities, even in the absence of medical causation. Such presumptions almost universally favor a determination of work-relatedness, but are rebuttable by competent contrary evidence. Rarely, agencies may enact a rebuttable presumption that a condition is not work-related. For instance, a state might establish an irrefutable presumption that lung cancers are work-related if they occur among firefighters; accordingly, the development of pulmonary adenocarcinoma by a firefighter would be presumptively work-related. Conversely, a legislature may create a presumption that the development of lung cancer among firefighters who have at least a 10 pack-year cigarette smoking history is not work-related. Consequently, even a firefighter with significant workplace exposure to a known carcinogen would be presumptively not work-related, if the firefighter's smoking history meets the minimum criterion. Workers’ compensation systems may also weight the opinions of providers differently. A treating physician's causation opinion, regardless of qualifications, may supersede that of a consulting physician with specific subject matter expertise; therefore, the court may disregard a consulting physician's opinion and rely on the treating physician's opinion, irrespective of either the treating physician's qualifications or the rigor of his or her methodology for determination of causation. DETERMINATION OF CAUSATION In evaluating traumatic injuries, the etiology of which is not in dispute (eg, fracture or dislocation), or the acute occurrences of disease (eg, acute carbon monoxide toxicity), may not demand the same rigorous evaluation of work-relatedness as an occupational disease. Establishing the causality of disease may be difficult, especially if it is necessary to determine whether an employee's disease was caused by, or alternatively, aggravated by an occupational exposure. In contrast to a traumatic injury, a cause–effect relationship between disease and an occupational exposure may not be clear. Occupational diseases may develop insidiously. Symptoms of disease may be confused with age-related symptoms or effects caused by other relevant factors—personal health attributes or avocational exposures. Information on prior occupational exposures is often unavailable, inadequate, or incomplete. Individual susceptibility to similar exposures to disease-producing agents may influence causation decisions. Avocational exposures may be either a primary or contributory cause. Clinical evaluations frequently commence with a presumption of work-relatedness, a cursory determination of work-relatedness, or even no evaluation of work-relatedness. Under certain circumstances, clinicians may be concerned primarily with accurate differential diagnosis and prescription of efficacious treatment.3 However, what appears to be obvious is often subject to controversy, particularly in compensation environments; accordingly, it is important to compile complete and accurate information, if possible, to assure an equitable work-relatedness decision. An inability to identify a nonoccupational cause for the subject condition (eg, an avocational exposure or personal health attribute) should not result in a default conclusion that the adverse health effect is work-related. GENERAL AND SPECIFIC CAUSATION Epidemiological evidence establishing that a risk factor is generally capable of causing the plaintiff's adverse health outcome is insufficient evidence that an individual's adverse health consequence was specifically caused by the exposures of interest. For example, evidence of an inadvertent chemical release into the ecosystem, coupled with epidemiological evidence of a causal association between such chemicals and the subject disease, is insufficient evidence that the release caused an adverse health consequence, absent evidence that the individual was exposed to a sufficient magnitude of exposure to the chemical to cause the adverse health effect; the temporal (chronological) relationship between exposure and effect is biologically plausible; and other known and biologically plausible causes have been excluded. PRIMARY CF. MULTIFACTORIAL CAUSATION The physician may determine that a workplace factor is the primary cause or one of several contributory causes (ie, multifactorial). Each factor could either independently produce a disease or disorder, or there may be a synergy among multiple factors. A direct cause can generally be attributed if both an immediate trauma and the effect are clearly observable. If an obvious and direct relationship exists between an injury and an external energy source, such as a moving or falling object (kinetic energy), a fall (potential energy), a chemical burn (chemical energy), or an electric shock or radiation (electromagnetic energy), a sole direct cause exists. Health conditions often develop due to a combination of factors, only some of which may be work-related. For instance, hearing loss may occur as a result of aging, cardiovascular disease, and occupational noise exposure. Additionally, occupational and nonoccupational factors may have a synergistic effect (eg, carpal tunnel syndrome developing in the context of simultaneous exertional job requirements, obesity, and diabetes mellitus). Cases may also develop following exposures arising from both nonoccupational and work-related activities. Personal factors also can be part of the “web of causation.” For example, there is evidence that wrist width-depth ratio is a risk for carpal tunnel syndrome.4–6 In these circumstances, physicians are obliged to assess whether causality is truly multifactorial or whether there is a predominant cause among many factors. Competing causation differs from combined causation in that either a workplace factor or a nonoccupational factor, but not both, is independently responsible for the adverse health effect. For example, because pregnancy, diabetes mellitus, thyroid disorders, tobacco, and repetitive forceful motions have been independently associated with carpal tunnel syndrome (CTS), a patient with diabetes who does very little forceful, repetitive work will most likely develop carpal tunnel syndrome due to the diabetes, not occupational exposure.7–18 In both primary and multifactorial causation, it is essential to attain a thorough understanding of the patient's exact work activities, as well as to compare the work activities with exposures reported in the quality epidemiological literature and metrics established by exposure standards, eg, the Occupational Safety and Health Administration (OSHA), International Organization for Standardization (ISO), American National Standards Institute (ANSI), and the World Health Organization (WHO) standards and guidelines). Identifying a condition in coworkers may be informative (particularly when the outcome is rare) in assessing competing and combined causation. For instance, bronchiolitis obliterans among popcorn workers or other diacetyl-exposed workers markedly increases the probability of a causal linkage. When disorders are common and multifactorial, identifying other workplace cases may be meaningful, especially when adjusted rates are valid and statistically elevated. For example, where there are elevated rates of CTS, consideration of occupational and nonoccupational factors permits physicians to understand both the operant biomechanical factors and assess whether the effects are manifest among coworkers, in addition to the patient, although at lesser levels (suggesting combined causation) or limited predominantly to the patient (suggesting competing causation with nonoccupational factors of greater significance than occupational factors). PRIMARY CF. CERTAINTY For medical purposes, different definitions of causation are used depending on the purpose of the assessment of work-relatedness. In the clinical setting, relatively specific case definitions are used to define occurrence (as described further in the ACOEM guidelines for individual conditions). In clinical practice, action based on the assessment of causal association and on the seriousness of the health effect may be commensurate with the degree of certainty about causation, based on available information on temporal, physiologic, and physical links between exposure and effect. In such cases, analytic reasoning not opinion should be used to link the populations-based epidemiological evidence with clinical findings and exposure data (see Independent Medical Examinations and Consultations guideline); otherwise, preventive efforts are unlikely to be effective. From a public health perspective, a reasonable probability of causation should lead to preventive actions whenever possible. Physicians can weigh the costs and benefits of the intervention against the degree of certainty of causation (eg, an ergonomics evaluation of a worksite could be triggered by worker complaints of discomfort; whereas, removing a worker from a job generally requires more study and associated certainty). In contrast, bronchiolitis obliterans in a diacetyl-exposed worker should prompt a rapid analysis and preventive interventions. The physician's opinion on the absolute probability that a disease or disorder is work-related should not be affected by administrative or legal context; however, a statement of probability related to compensability must incorporate both the absolute probability as well as the administrative or legal context. The term “more likely than not” (equal to or greater than 51%) is a legal and not medical term that must be used as defined and intended. Disorders presented for causal analysis might represent reoccurrence of a previously resolved condition or exacerbation (ie, aggravation) of a pre-existing condition. The distinction between a recurrence, or aggravation of a condition is medically and legally important. Substantial confusion has been engendered by the ambiguous and inconsistent use of such terminology in worker's compensation statutes, which seldom operationally define such terms. Aggravation could be construed as manifestation of symptoms, exacerbation of symptoms, or a progression, natural or otherwise, of underlying pathology. Aggravation and exacerbation are synonymous. Precipitation could be construed as manifestation, natural or otherwise, of underlying pathology, whether previously or of symptoms as the result of occupational exposures is of both occupational and nonoccupational and of symptoms with occupational does not work-relatedness or of trauma can be on prior work-related and If an underlying condition is it is important to the due to the factors. prior levels is a of When and if that is the aggravation is to have Because an aggravation of a pre-existing condition by to a permanent in the patient's underlying the work-related injury or disease is not of whether a to work there remains a for future of symptoms it depending the compensation be necessary to determine whether is due to an or exposure or the natural of the pre-existing condition. OF CAUSATION A causation analysis is generally or the clinical Although the physician is to information may be or especially in compensation However, a opinion as to causation may be necessary in many to and to determine whether compensation or other benefits will be even if causation has not been The case analysis is often a more information about individual and prior and medical other medical information and scientific literature is often An causal based on in of will be important in most The to the determination of work-relatedness, as by the National Institute for Occupational Safety and Health of of the following of disease. is the certainty is there that the diagnosis is evidence or to that the diagnosis a generally case criteria is the epidemiological evidence for that there for a relationship with of individual exposure. evidence is there that the of the patient's exposure is of the and temporal of exposure associated with of other relevant factors. other causal factors are For example, is the worker with carpal tunnel syndrome or of the opinions and and If an opinion has been is the to that there for the basis of the that the attributed to of the information and the that there information that that the information is for example, from a (eg, exposure This is a of the This a to however, evaluation of the specific evidence available is important and requires a For a relatively case definition is frequently This may the of for but generally produces a of If cause and more can be to evaluate and an The definition of causal association is more that the causal relationship is not statistically scientific literature about and other occupational disorders causal with work exposures is frequently it to whether risk factors statistically associated with or of certain adverse health in causal The methodology for a causal association is in for Epidemiological of a OF The and public health have generally criteria to assess the evidence for the work-relatedness of adverse health These criteria should for preventive to evaluate the effects of exposures for and The of the following criteria are generally the most association between the exposure or work factor and the health (ie, the exposure the development of of the association (eg, is the risk or ratio exposed to (ie, risk at least levels of of the association among multiple epidemiological of the association with in exposure levels and other of the association that the exposure causes one specific health than a of of the relationship (eg, that the with or of evidence from of the association in future cases of the disease. Physicians must be specific about the and temporal of exposures that might be associated with a specific adverse health OF CAUSATION If the causal effect on the patient is immediate and (eg, a causation is causation to a or chemical work factor requires epidemiological evidence that a of work-relatedness is associated with an individual's The of the exposure and effect is but not Although a assessment is often based on limited it must be as it and state and injury (eg, injury Information to a analysis may be available at the of the but information is almost The minimum assessment of for preventive purposes, may be based on a however, the degree of should be clearly to the patient, state or The of the clinical assessment are a diagnosis to specific criteria including reported symptoms, clinical and workplace exposure the of a compensation and whether other causal factors are The with the patient is the to or The patient's of acute is most accurate following an Information for the analysis of causation often from other or is in medical or weight to the most proximate AND A medical history is essential to consideration of the work-relatedness of a the that is the of the or to be the of the exposure. This the of a of and symptoms and an occupational exposure. This information can into occupational, nonoccupational, and factors that might influence (ie, to an injury, disease, or is also necessary to a history in where the patient with or is often necessary when there is a of or to from exposure. link between exposures and health effects is temporal The temporal exposure and trauma and symptoms should be Although the of or conditions may be should be should be to and whether the exposure the of Although the and of symptoms on on or other that the patient is not should be temporal causality might be for diseases and disorders and certain For example, symptoms of disorder may be for some to the cause of the and symptoms often improve or other of to physical is actually and the relationship between and work factors is exposures to be by valid and The patient may his or her and any the of however, information concerning both exposure and symptoms is not in compensation might in in physical or chemical the absence or of or personal The relevant personal tobacco, prescription (eg, and with adverse health disease and The patient should also be about similar occupational or nonoccupational and in the activities should be particularly the patient's in activities or that could similar symptoms or When a worker's the should be to there a temporal relationship between the exposure and the work exposure occur the health If was the that between the exposure and putative effect the epidemiological evidence, the of the exposure the and temporal of the exposure sufficient to cause an effect in most If was the of the exposure sufficient to cause an effect in this worker (ie, does the worker have any the association with work with or evidence as to the or disorder could develop the of the of the case must also be other causes or for the illness, or injury in the exposure have been by personal or other the health effect causing or Although causation may be or in many based on the patient's a more exposure history is necessary to the assessment and or This is especially in cases where the injury or disease is not but may be to exposure than an In such should be to information about workplace or other exposures. For disorders, this particularly a of the exertional of the job work and of the exertional of the The might about the of on a the of specific motions or and job and other factors, such as the of and other factors that might the exertional of the For and should be on of symptoms, with the and temporal of exposure. Information from the patient should be by information from the of from coworkers and may in or a patient's and of health effects from Safety may in the clinical and literature exposures to or exposures is often necessary to causation. Although to determine whether or not a or is are a common are often to determine the and temporal of exposure. The for and agents (eg, are and by relevant epidemiological data or by or state or generally and standards (eg, If possible, should be with the of the than to exposure. If must be some that conditions have not is in to have some degree of that the relationship is A worksite by the physician may be on the by an occupational physical or occupational may be to Personal data are generally the most data to and exposure If personal data or data of a are unavailable, data are the data should be at a or when exposures would be to most worksite further information that is available for exposure such as job and in relationship to of disease of job and data personal can be A assessment would require evidence of exposure to factors at levels known to produce the specific adverse health effects in of causal analysis often requires more information than is available at the that are A and thorough medical history must be and relevant pre-existing symptoms, injuries, and disorders should be and The of information for the history may be the patient, medical from other prior medical or medical and are For of injuries, the most proximate are greater weight than with In many cases, a of the literature may be to the evidence exposure to health may be to the of complaints or health A of the scientific literature may a of association between the exposures and the patient's health effect. In most should be based on workers in similar or may be to the of the patient in including exposure with quality exposure In the scientific the following case definitions among a in or disease be by a in or of the or is the quality of the available the or is the quality of the study (eg, clinical or generally to for epidemiological (see of information worker effects or similar and and is the specific of the there a or statistically is the rigor of the it it the quality study is the quality quality that they have no from and determination of work-relatedness. to the of and is important to a of the literature than on a study or only that a of If the are inadequate, it may be necessary to to among In assessing the of to the patient's the physician may the of the specific of (eg, to be into effects in several more weight than a in a In the absence of in the epidemiological literature for a causal relationship between a disease and a of or injury, the of similarly defined cases in the same worksite may a of work-relatedness, but may also due to case (eg, conditions such as or carpal tunnel syndrome may result in information including and which are not or factors (eg, which may be associated with complaints such as and case be without further If several cases are the of of at can be If are more of the exposed and should the health effect is (eg, of the or lung that the is not The determination of work-relatedness should a reproducible method for including and occupational, exposure and other evidence. of work-relatedness are important to assure workers benefits (eg, compensation are if there is a and causal as well as to and of the condition where there is elevated risk is and when preventive efforts are to other workers similar An assessment of work-relatedness is at the patient's clinical A work-relatedness determination is generally for acute traumatic injuries, but more for complaints and occupational The assessment therefore, be including information from the patient, other medical exposure epidemiological other and the worksite are for a causal assessment of occupational diseases and the of the individual assessing work-relatedness may lead to preventive including personal administrative or If work causes or to and the exposure be the worker may be the preventive efforts may workers in similar from and other cases of occupational or injury. Determination of work-relatedness is the for compensation determination should be and evidence-based.