Occupational disease and injury surveillance entails the systematic monitoring of health events in working populations in order to prevent and control occupational hazards and their associated diseases and injuries. Occupational disease and injury surveillance has four essential components (Baker, Melius and Millar 1988; Baker 1986).

1. Gather information on cases of occupational diseases and injuries.
2. Distil and analyse the data.
3. Disseminate organized data to necessary parties, including workers, unions, employers, governmental agencies and the public.
4. Intervene on the basis of data to alter the factors that produced these health events.

Surveillance in occupational health has been more concisely described as counting, evaluating and acting (Landrigan 1989).

Surveillance commonly refers to two broad sets of activities in occupational health. Public health surveillance refers to activities undertaken by federal, state or local governments within their respective jurisdictions to monitor and to follow up on occupational diseases and injuries. This type of surveillance is based on a population, that is, the working public. The recorded events are suspected or established diagnoses of occupational illness and injury. This article will examine these activities.

Medical surveillance refers to the application of medical tests and procedures to individual workers who may be at risk for occupational morbidity, to determine whether an occupational disorder may be present. Medical surveillance is generally broad in scope and represents the first step in ascertaining the presence of a work-related problem. If an individual or a population is exposed to a toxin with known effects, and if the tests and procedures are highly targeted to detect the likely presence of one or more effects in these persons, then this surveillance activity is more aptly described as medical screening (Halperin and Frazier 1985). A medical surveillance programme applies tests and procedures on a group of workers with common exposures for the purpose of identifying individuals who may have occupational illnesses and for the purpose of detecting patterns of illness which may be produced by occupational exposures among the programme participants. Such a programme is usually undertaken under the auspices of the individual’s employer or union.

Functions of Occupational Health Surveillance

Foremost among the purposes of occupational health surveillance is to identify the incidence and prevalence of known occupational diseases and injuries. Gathering descriptive epidemiological data on the incidence and prevalence of these diseases on an accurate and comprehensive basis is an essential prerequisite for establishing a rational approach to the control of occupational disease and injury. Assessment of the nature, magnitude and distribution of occupational disease and injury in any geographic area requires a sound epidemiological database. It is only through an epidemiological assessment of the dimensions of occupational disease that its importance relative to other public health problems, its claim for resources and the urgency of legal standard setting can be reasonably evaluated. Second, the collection of incidence and prevalence data allows analysis of trends of occupational disease and injury among different groups, at different places and during different time periods. Detecting such trends is useful for determining control and research priorities and strategies, and for evaluating the effectiveness of any interventions undertaken (Baker, Melius and Millar 1988).

A second broad function of occupational health surveillance is to identify individual cases of occupational disease and injury in order to find and evaluate other individuals from the same workplaces who may be at risk for similar disease and injury. Also, this process permits the initiation of control activities to ameliorate the hazardous conditions associated with causation of the index case (Baker, Melius and Millar 1988; Baker, Honchar and Fine 1989).An index case of occupational disease or injury is defined as the first ill or injured individual from a given workplace to receive medical care and thereby to draw attention to the existence of a workplace hazard and an additional workplace population at risk. A further purpose of case identification may be to assure that the affected individual receives appropriate clinical follow-up, an important consideration in view of the scarcity of clinical occupational medicine specialists (Markowitz et al. 1989; Castorino and Rosenstock 1992).

Finally, occupational health surveillance is an important means of discovering new associations between occupational agents and accompanying diseases, since the potential toxicity of most chemicals used in the workplace is not known. Discovery of rare diseases, patterns of common diseases or suspicious exposure-disease associations through surveillance activities in the workplace can provide vital leads for a more conclusive scientific evaluation of the problem and possible verification of new occupational diseases.

Obstacles to the Recognition of Occupational Diseases

Several important factors undermine the ability of occupational disease surveillance and reporting systems to fulfil the functions cited above. First, recognition of the underlying cause or causes of any illness is the sine qua non for recording and reporting occupational diseases. However, in a traditional medical model that emphasizes symptomatic and curative care, identifying and eliminating the underlying cause of illness may not be a priority. Furthermore, health care providers are often not adequately trained to suspect work as a cause of disease (Rosenstock 1981) and do not routinely obtain histories of occupational exposure from their patients (Institute of Medicine 1988). This should not be surprising, given that in the United States, the average medical student receives only six hours of training in occupational medicine during the four years of medical school (Burstein and Levy 1994).

Certain features characteristic of occupational disease exacerbate the difficulty of recognizing occupational diseases. With few exceptions—most notably, angiosarcoma of the liver, malignant mesothelioma and the pneumoconioses—most diseases that can be caused by occupational exposures also have non-occupational causes. This non-specificity renders difficult the determination of the occupational contribution to disease occurrence. Indeed, the interaction of occupational exposures with other risk factors may greatly increase the risk of disease, as occurs with asbestos exposure and cigarette smoking. For chronic occupational diseases such as cancer and chronic respiratory disease, there usually exists a long period of latency between onset of occupational exposure and presentation of clinical disease. For example, malignant mesothelioma typically has a latency of 35 years or more. A worker so affected may well have retired, further diminishing a physician’s suspicion of possible occupational aetiologies.

Another cause of the widespread under-recognition of occupational disease is that the majority of chemicals in commerce have never been evaluated with regard to their potential toxicity. A study by the National Research Council in the United States in the 1980s found no information available on the toxicity of approximately 80% of the 60,000 chemical substances in commercial use. Even for those groups of substances that are most closely regulated and about which the most information is available—drugs and food additives—reasonably complete information on possibly untoward effects is available for only a minority of agents (NRC 1984).

Workers may have a limited ability to provide an accurate report of their toxic exposures. Despite some improvement in countries such as the United States in the 1980s, many workers are not informed of the hazardous nature of the materials with which they work. Even when such information is provided, recalling the extent of exposure to multiple agents in a variety of jobs over a working career may be difficult. As a result, even health care providers who are motivated to obtain occupational information from their patients may not be able to do so.

Employers may be an excellent source of information regarding occupational exposures and the occurrence of work-related diseases. However, many employers do not have the expertise to assess the extent of exposure in the workplace or to determine whether an illness is work related. In addition, financial disincentives to finding that a disease is occupational in origin may discourage employers from using such information appropriately. The potential conflict of interest between the financial health of the employer and the physical and mental health of the worker represents a major obstacle to improving surveillance of occupational disease.

Registries and other Data Sources Specific for Occupational Diseases

International registries

International registries for occupational diseases are an exciting development in occupational health. The obvious benefit of these registries is the ability to conduct large studies, which would allow determination of the risk of rare diseases. Two such registries for occupational diseases were initiated during the 1980s.

The International Agency for Research on Cancer (IARC) established the International Register of Persons Exposed to Phenoxy Herbicides and Contaminants in 1984 (IARC 1990). As of 1990, it had enrolled 18,972 workers from 19 cohorts in ten countries. By definition all enrolees worked in industries involving phenoxy herbicides and/or chlorophenols, principally in manufacturing/formulating industries or as applicators. Exposure estimates have been made for participating cohorts (Kauppinen et al. 1993), but analyses of cancer incidence and mortality have not yet been published.

An international registry of cases of angiosarcoma of the liver (ASL) is being coordinated by Bennett of ICI Chemicals and Polymers Limited in England. Occupational exposure to vinyl chloride is the only known cause of angiosarcoma of the liver. Cases are reported by a voluntary group of scientists from companies producing vinyl chloride, governmental agencies and universities. As of 1990, 157 cases of ASL with dates of diagnosis between 1951 and 1990 were reported to the registry from 11 countries or regions. Table 1 also shows that most of the recorded cases were reported from countries where facilities started polyvinyl chloride manufacture before 1950. The registry has recorded six clusters of ten or more cases of ASL at facilities in North America and Europe (Bennett 1990).

Table 1. Number of cases of angiosarcoma of the liver in the world register by country and year of first production of vinyl chloride

Source: Bennett, B. World Register of Cases of Angiosarcoma of the Liver (ASL)
due to Vinyl Chloride Monomer, January 1, 1990.

Governmental surveys

Employers are sometimes legally required to record occupational injuries and illnesses that occur in their facilities. Like other workplace-based information, such as numbers of employees, wages and overtime, injury and illness data may be systematically collected by governmental agencies for the purpose of surveillance of work-related health outcomes.

In the United States, the Bureau of Labor Statistics (BLS) of the US Department of Labor has conducted the Annual Survey of Occupational Injuries and Illnesses (BLS Annual Survey) since 1972 as required by the Occupational Safety and Health Act (BLS 1993b). The goal of the survey is to obtain the numbers and the rates of illnesses and injuries recorded by private employers as being occupational in origin (BLS 1986). The BLS Annual Survey excludes employees of farms with fewer than 11 employees, the self-employed and employees of the federal, state and local governments. For the most recent year available, 1992, the survey reflects questionnaire data obtained from a stratified random sample of approximately 250,000 establishments in the private sector in the United States (BLS 1994).

The BLS survey questionnaire completed by the employer is derived from a written record of occupational injuries and illnesses which employers are required to maintain by the Occupational Safety and Health Administration (OSHA 200 Log). Although OSHA mandates that the employer keep the 200 Log for examination by an OSHA inspector upon request, it does not require that employers routinely report the log’s contents to OSHA, except for the sample of employers included in the BLS Annual Survey (BLS 1986).

Some well-recognized weaknesses severely limit the ability of the BLS survey to provide a full and accurate count of occupational illnesses in the United States (Pollack and Keimig 1987). Data are employer derived. Any illness that the employee does not report to the employer as being work related will not be reported by the employer on the annual survey. Among active workers, such a failure to report may be due to fear of consequences to the employee. Another major obstacle to reporting is the failure of the employee’s physician to diagnose illness as being work related, especially for chronic diseases. Occupational diseases occurring among retired workers are not subject to the BLS reporting requirement. Indeed, it is unlikely that the employer would be aware of the onset of a work-related illness in a retiree. Since many cases of chronic occupational illnesses with long latency, including cancer and lung disease, are likely to have their onset following retirement, a large proportion of such cases would not be included in the data collected by the BLS. These limitations were recognized by BLS in a recent report on its annual survey (BLS 1993a). In response to recommendations by the National Academy of Sciences, the BLS re-designed and implemented a new annual survey in 1992.

According to the 1992 BLS Annual Survey, there were 457,400 occupational illnesses in private industry in the United States (BLS 1994). This represented a 24% increase, or 89,100 cases, over the 368,300 illnesses recorded in the 1991 BLS Annual Survey. The incidence of new occupational illnesses was 60.0 per 10,000 workers in 1992.

Disorders associated with repeated trauma, such as carpal tunnel syndrome, tendonitis of the wrist and elbow and hearing loss, dominate the occupational illnesses recorded in the BLS Annual survey and have done so since 1987 (table 2). In 1992, they accounted for 62% of all illness cases recorded on the annual survey. Other important categories of disease were skin disorders, pulmonary diseases and disorders associated with physical trauma.

Table 2. Number of new cases of occupational illness by category of illness-US Bureau of Labor Statistics Annual Survey, 1986 versus 1992.

Sources: Occupational Injuries and Illnesses in the United States by Industry, 1991.
US Department of Labor, Bureau of Labor Statistics, May 1993. Unpublished data,
US Department of Labor, Bureau of Labor Statistics, December, 1994.

Although disorders associated with repeated trauma clearly account for the largest proportion of the increase in cases of occupational illness, there was also a 50% increase in the recorded incidence in occupational illnesses other than those due to repeated trauma in the six years between 1986 and 1992, during which employment in the United States rose by just 8.7%.

These increases in the numbers and rates of occupational diseases recorded by employers and reported to the BLS in recent years in the United States are remarkable. The rapid change in the recording of occupational illnesses in the United States is due to a change in the underlying occurrence of disease and to a change in the recognition and reporting of these conditions. By comparison, during the same time period, 1986 to 1991, the rate of occupational injuries per 100 full-time workers recorded by the BLS went from 7.7 in 1986 to 7.9 in 1991, a mere 2.6% increase. The number of recorded fatalities in the workplace has likewise not increased dramatically in the first half of the 1990s.

Employer-based surveillance

Apart from the BLS survey, many US employers conduct medical surveillance of their workforces and thereby generate a vast amount of medical information that is relevant to the surveillance of occupational diseases. These surveillance programmes are undertaken for numerous purposes: to comply with OSHA regulations; to maintain a healthy workforce through the detection and treatment of non-occupational disorders; to ensure that the employee is fit to perform the tasks of the job, including the need to wear a respirator; and to conduct epidemiological surveillance to uncover patterns of exposure and disease. These activities utilize considerable resources and could potentially make a major contribution to the public health surveillance of occupational diseases. However, since these data are non-uniform, of uncertain quality and largely inaccessible outside the companies in which they are collected, their exploitation in occupational health surveillance has been realized on only a limited basis (Baker, Melius and Millar 1988).

OSHA also requires that employers perform selected medical surveillance tests for workers exposed to a limited number of toxic agents. Additionally, for fourteen well-recognized bladder and lung carcinogens, OSHA requires a physical examination and occupational and medical histories. The data collected under these OSHA provisions are not routinely reported to governmental agencies or other centralized data banks and are not accessible for the purposes of occupational disease reporting systems.

Surveillance of public employees

Occupational disease reporting systems may differ for public versus private employees. For example, in the United States, the annual survey of occupational illnesses and injuries conducted by the federal Department of Labor (BLS Annual Survey) excludes public employees. Such workers are, however, an important part of the workforce, representing approximately 17% (18.4 million workers) of the total workforce in 1991. Over three-fourths of these workers are employed by state and local governments.

In the United States, data on occupational illnesses among federal employees are collected by the Federal Occupational Workers’ Compensation Program. In 1993, there were 15,500 occupational disease awards to federal workers, yielding a rate of 51.7 cases of occupational illnesses per 10,000 full-time workers (Slighter 1994). At the state and local levels, the rates and numbers of illnesses due to occupation are available for selected states. A recent study of state and local employees in New Jersey, a sizeable industrial state, documented 1,700 occupational illnesses among state and local employees in 1990, yielding an incidence of 50 per 10,000 public-sector workers (Roche 1993). Notably, the rates of occupational disease among federal and non-federal public workers are remarkably congruent with the rates of such illness among private sector workers as recorded in the BLS Annual Survey. The distribution of illness by type differs for public versus private workers, a consequence of the different type of work that each sector performs.

Workers’ compensation reports

Workers’ compensation systems provide an intuitively appealing surveillance tool in occupational health, because the determination of work-relatedness of disease in such cases has presumably undergone expert review. Health conditions that are acute and easily recognized in origin are frequently recorded by workers’ compensation systems. Examples include poisonings, acute inhalation of respiratory toxins and dermatitis.

Unfortunately, the use of workers’ compensation records as a credible source for surveillance data is subject to severe limitations, including lack of standardization of eligibility requirements, deficiency of standard case definitions, disincentives to workers and employers to file claims, the lack of physician recognition of chronic occupational diseases with long latent periods and the usual gap of several years between initial filing and resolution of a claim. The net effect of these limitations is that there is significant under-recording of occupational disease by workers’ compensation systems.

Thus, in a study by Selikoff in the early 1980s, less than one-third of US insulators who were disabled by asbestos-related diseases, including asbestosis and cancer, had even filed for workers’ compensation benefits, and many fewer were successful in their claims (Selikoff 1982). Similarly, a US Department of Labor study of workers who reported disability from occupational disease found that less than 5% of these workers received workers’ compensation benefits (USDOL 1980). A more recent study in the state of New York found that the number of people admitted to hospitals for pneumoconioses vastly outnumbered the people who were newly awarded workers’ compensation benefits during a similar time period (Markowitz et al. 1989). Since workers’ compensation systems record simple health events such as dermatitis and musculoskeletal injuries much more readily than complex diseases of long latency, use of such data leads to a skewed picture of the true incidence and distribution of occupational diseases.

Laboratory reports

Clinical laboratories can be an excellent source of information on excessive levels of selected toxins in body fluids. Advantages of this source are timely reporting, quality-control programmes already in place and the leverage for compliance provided by the licensing of such laboratories by governmental agencies. In the United States, numerous states require that clinical laboratories report the results of selected categories of specimens to the state health departments. Occupational agents subject to this reporting requirement are lead, arsenic, cadmium and mercury as well as substances reflecting pesticide exposure (Markowitz 1992).

In the United States, the National Institute for Occupational Safety and Health (NIOSH) began to assemble the results of adult blood lead testing into the Adult Blood Lead Epidemiology and Surveillance programme in 1992 (Chowdhury, Fowler and Mycroft 1994). By the end of 1993, 20 states, representing 60% of the US population, were reporting elevated blood lead levels to NIOSH, and an additional 10 states were developing the capacity to collect and report blood lead data. In 1993, there were 11,240 adults with blood lead levels that equalled or exceeded 25 micrograms per decilitre of blood in the 20 reporting states. The vast majority of these individuals with elevated blood lead levels (over 90%) were exposed to lead at the workplace. Over one-quarter (3,199) of these individuals had blood leads greater than or equal to 40 ug/dl, the threshold at which the US Occupational Safety and Health Administration requires actions to protect workers from occupational lead exposure.

Reporting of elevated levels of toxins to the state health department may be followed by a public health investigation. Confidential follow-up interviews with affected individuals allows timely identification of the workplaces where exposure occurred, categorization of the case by occupation and industry, estimation of the number of other workers at the workplace potentially exposed to lead and assurance of medical follow-up (Baser and Marion 1990). Worksite visits are followed by recommendations for voluntary actions to reduce exposure or may lead to reporting to authorities with legal enforcement powers.

Physicians’ reports

In an attempt to replicate the strategy successfully utilized for the monitoring and control of infectious diseases, an increasing number of states in the United States require physicians to report one or more occupational diseases (Freund, Seligman and Chorba 1989). As of 1988, 32 states required reporting of occupational diseases, though these included ten states where only one occupational disease is reportable, usually lead or pesticide poisoning. In other states, such as Alaska and Maryland, all occupational diseases are reportable. In most states, reported cases are used only to count the number of people in the state affected by the disease. In only one-third of the states with reportable disease requirements does a report of a case of occupational disease lead to follow-up activities, such as workplace inspection (Muldoon, Wintermeyer and Eure 1987).

Despite the evidence of increased recent interest, physician reporting of occupational diseases to appropriate state governmental authorities is widely acknowledged to be inadequate (Pollack and Keimig 1987; Wegman and Froines 1985). Even in California, where a system for physician reporting has been in place for a number of years (Doctor’s First Report of Occupational Illness and Injury) and recorded nearly 50,000 occupational illnesses in 1988, physician compliance with reporting is regarded as incomplete (BLS 1989).

A promising innovation in occupational health surveillance in the United States is the emergence of the concept of the sentinel provider, part of an initiative undertaken by NIOSH called Sentinel Event Notification System for Occupational Risks (SENSOR). A sentinel provider is a physician or other health care provider or facility that is likely to provide care for workers with occupational disorders due to the provider’s specialty or geographic location.

Since sentinel providers represent a small subset of all health care providers, health departments can feasibly organize an active occupational disease reporting system by performing outreach, offering education and providing timely feedback to sentinel providers. In a recent report from three states participating in the SENSOR programme, physician reports of occupational asthma increased sharply after the state health departments developed concerted educational and outreach programmes to identify and recruit sentinel providers (Matte, Hoffman and Rosenman 1990).

Specialized occupational health clinical facilities

A newly emergent resource for occupational health surveillance has been the development of occupational health clinical centres that are independent of the workplace and that specialize in the diagnosis and treatment of occupational disease. Several dozen such facilities currently exist in the United States. These clinical centres can play several roles in enhancing occupational health surveillance (Welch 1989). First, the clinics can play a primary role in case-finding—that is, identifying occupational sentinel health events—since they represent a unique organizational source of expertise in clinical occupational medicine. Second, the occupational health clinical centres can serve as a laboratory for the development and refinement of surveillance case definitions for occupational disease. Third, the occupational health clinics can serve as a primary clinical referral resource for the diagnosis and evaluation of workers who are employed at a worksite where an index case of occupational disease has been identified.

Occupational health clinics have become organized into a national association in the United States (the Association of Occupational and Environmental Clinics) to enhance their visibility and to collaborate on research and clinical investigations (Welch 1989). In some states, such as New York, a statewide network of clinical centres has been organized by the state health department and receives stable funding from a surcharge on workers’ compensation premiums (Markowitz et al. 1989). The clinical centres in New York State have collaborated in the development of information systems, clinical protocols and professional education and are beginning to generate substantial data on the numbers of cases of occupational disease in the state.

Use of Vital Statistics and Other General Health Data

Death certificates

The death certificate is a potentially very useful instrument for occupational disease surveillance in many countries in the world. Most countries have death registries. Uniformity and comparability is promoted by the common use of the International Classification of Diseases to identify cause of death. Furthermore, many jurisdictions include information on death certificates concerning the occupation and industry of the deceased. A major limitation in the use of death certificates for occupational disease surveillance is the lack of unique relationships between occupational exposures and specific causes of death.

The use of mortality data for occupational disease surveillance is most salient for diseases that are uniquely caused by occupational exposures. These include the pneumoconioses and one type of cancer, malignant mesothelioma of the pleura. Table 3 shows the numbers of deaths attributed to these diagnoses as the underlying cause of death and as one of multiple causes of death listed on the death certificate in the United States. The underlying cause of death is considered the principal cause for death, while the listing of multiple causes includes all conditions considered important in contributing to death.

Table 3. Deaths due to pneumoconiosis and malignant mesothelioma of the pleura. Underlying cause and multiple causes, United States, 1990 and 1991

Source: United States National Center for Health Statistics.

In 1991, there were 1,237 deaths due to the dust diseases of the lung as the underlying cause, including 693 deaths due to coal workers pneumoconioses and 269 deaths due to asbestosis. For malignant mesothelioma, there was a total of 452 deaths due to pleural mesothelioma. It is not possible to identify the number of deaths due to malignant mesothelioma of the peritoneum, also caused by occupational exposure to asbestos, since International Classification of Disease codes are not specific for malignant mesothelioma of this site.

Table 3 also shows the numbers of deaths in the United States in 1990 due to pneumoconioses and malignant mesothelioma of the pleura when they appear as one of multiple causes of death on the death certificate. For the pneumoconioses, the total where they appear as one of multiple causes is important, since the pneumoconioses often co-exist with other chronic lung diseases.

An important issue is the extent to which pneumoconioses may be under-diagnosed and, therefore, missing from death certificates. The most extensive analysis of the under-diagnosis of a pneumoconiosis has been performed among insulators in the United States and Canada by Selikoff and colleagues (Selikoff, Hammond and Seidman 1979; Selikoff and Seidman 1991). Between 1977 and 1986, there were 123 insulator deaths ascribed to asbestosis on the death certificates. When investigators reviewed medical records, chest radiographs and tissue pathology where available, they ascribed 259 of insulator deaths occurring in these years to asbestosis. Over one-half of pneumoconiosis deaths were, thus, missed in this group well-known to have heavy asbestos exposure. Unfortunately, there are not a sufficient number of other studies of the under-diagnosis of pneumoconioses on death certificates to allow a reliable correction of mortality statistics.

Deaths due to causes that are not specific to occupational exposures have also been used as part of occupational disease surveillance when occupation or industry of decedents is recorded on the death certificates. Analysis of these data in a specified geographical area during a selected time period can yield rates and ratios of disease by cause for different occupations and industries. The role of non-occupational factors in the deaths examined cannot be defined by this approach. However, differences in rates of disease in different occupations and industries suggest that occupational factors may be important and provide leads for more detailed studies. Other advantages of this approach include the ability to study occupations that are usually distributed among many workplaces (e.g., cooks or dry cleaner workers), the use of routinely collected data, a large sample size, relatively low expense and an important health outcome (Baker, Melius and Millar 1988; Dubrow, Sestito and Lalich 1987; Melius, Sestito and Seligman 1989).

Such occupational mortality studies have been published over the past several decades in Canada (Gallagher et al. 1989), Great Britain (Registrar General 1986), and the United States (Guralnick 1962, 1963a and 1963b). In recent years, Milham utilized this approach to examine the occupational distribution of all men who died between 1950 and 1979 in the state of Washington in the United States. He compared the proportion of all deaths due to any specific cause for one occupational group with the relevant proportion for all occupations. Proportional mortality ratios are thereby obtained (Milham 1983). As an example of the yield of this approach, Milham noted that 10 of 11 occupations with probable exposure to electrical and magnetic fields showed an elevation in the proportional mortality ratio for leukaemia (Milham 1982). This was one of the first studies of the relationship between occupational exposure to electro-magnetic radiation and cancer and has been followed by numerous studies that have corroborated the original finding (Pearce et al. 1985; McDowell 1983; Linet, Malker and McLaughlin 1988).

As a result of a cooperative effort between NIOSH, the National Cancer Institute, and the National Center for Health Statistics during the 1980s, analyses of the mortality patterns by occupation and industry between 1984 and 1988 in 24 states in the United States have recently been published (Robinson et al. 1995). These studies evaluated 1.7 million deaths. They confirmed several well-known exposure-disease relationships and reported new associations between selected occupations and specific causes of death. The authors emphasize that occupational mortality studies may be useful to develop new leads for further study, to evaluate results of other studies and to identify opportunities for health promotion.

More recently, Figgs and colleagues at the US National Cancer Institute used this 24-state occupational mortality database to examine occupational associations with non-Hodgkin’s lymphoma (NHL) (Figgs, Dosemeci and Blair 1995). A case-control analysis involving approximately 24,000 NHL deaths occurring between 1984 and 1989 confirmed previously demonstrated excess risks of NHL among farmers, mechanics, welders, repairmen, machine operators and a number of white-collar occupations.

Hospital discharge data

Diagnoses of hospitalized patients represent an excellent source of data for the surveillance of occupational diseases. Recent studies in several states in the United States show that hospital discharge data can be more sensitive than workers’ compensation records and vital statistics data in detecting cases of diseases that are specific to occupational settings, such as the pneumoconioses (Markowitz et al. 1989; Rosenman 1988). In New York State, for example, an annual average of 1,049 people were hospitalized for pneumoconioses in the mid-1980s, compared to 193 newly awarded workers’ compensation cases and 95 recorded deaths from these diseases each year during a similar time interval (Markowitz et al. 1989).

In addition to providing a more accurate count of the number of people ill with selected serious occupational diseases, hospital discharge data can be usefully followed up to detect and to alter workplace conditions that caused the disease. Thus, Rosenman evaluated workplaces in New Jersey where individuals who were hospitalized for silicosis had previously worked and found that the majority of these workplaces had never performed air sampling for silica, had never been inspected by the federal regulatory authority (OSHA) and did not perform medical surveillance for the detection of silicosis (Rosenman 1988).

Advantages of using hospital discharge data for the surveillance of occupational disease are their availability, low cost, relative sensitivity to serious illness and reasonable accuracy. Important disadvantages include the lack of information on occupation and industry and uncertain quality control (Melius, Sestito and Seligman 1989; Rosenman 1988). In addition, only individuals with disease sufficiently severe to require hospitalization will be included in the database and, therefore, cannot reflect the full spectrum of morbidity associated with occupational diseases. Nonetheless, it is likely that hospital discharge data will be increasingly used in occupational health surveillance in future years.

National surveys

Special surveillance surveys undertaken on a national or regional basis can be the source of information more detailed than can be obtained through use of routine vital records. In the United States, the National Center for Health Statistics (NCHS) conducts two periodic national health surveys relevant to occupational health surveillance: the National Health Interview Survey (NHIS) and the National Health and Nutrition Examination Survey (NHANES). The National Health Interview Survey is a national household survey designed to obtain estimates of the prevalence of health conditions from a representative sample of households reflecting the civilian non-institutionalized population of the United States (USDHHS 1980). A chief limitation of this survey is its reliance on self-reporting of health conditions. Occupational and industrial data on participating individuals have been used in the past decade for evaluating rates of disability by occupation and industry (USDHHS 1980), assessing the prevalence of cigarette smoking by occupation (Brackbill, Frazier and Shilling 1988) and recording workers’ views about the occupational risks that they face (Shilling and Brackbill 1987).

With the assistance of NIOSH, an Occupational Health Supplement (NHIS-OHS) was included in 1988 in order to obtain population-based estimates of the prevalence of selected conditions that may be associated with work (USDHHS 1993). Approximately 50,000 households were sampled in 1988, and 27,408 currently employed individuals were interviewed. Among the health conditions addressed by the NHIS-OHS are work-related injuries, dermatologic conditions, cumulative trauma disorders, eye, nose and throat irritation, hearing loss and low-back pain.

In the first completed analysis from the NHIS-OHS, Tanaka and colleagues from NIOSH estimated that the national prevalence of work-related carpal tunnel syndrome in 1988 was 356,000 cases (Tanaka et al. 1995). Of the estimated 675,000 people with prolonged hand pain and medically diagnosed carpal tunnel syndrome, over 50% reported that their health care provider had stated that their wrist condition was caused by workplace activities. This estimate does not include workers who had not worked in the 12 months prior to the survey and who may have been disabled due to work-related carpal tunnel syndrome.

In contrast to the NHIS, the NHANES directly assesses the health of a probability sample of 30,000 to 40,000 individuals in the United States by performing physical examinations and laboratory tests in addition to collecting questionnaire information. The NHANES was conducted twice in the 1970s and most recently in 1988. The NHANES II, which was conducted in the late 1970s, collected limited information on indicators of exposure to lead and selected pesticides. Initiated in 1988, the NHANES III collected additional data on occupational exposures and disease, especially concerning respiratory and neurologic disease of occupational origin (USDHHS 1994).

Summary

Occupational disease surveillance and reporting systems have significantly improved since the mid-1980s. Recording of illnesses is best for diseases unique or virtually unique to occupational causes, such as the pneumoconioses and malignant mesothelioma. Identification and reporting of other occupational diseases depends upon the ability to match occupational exposures with health outcomes. Many data sources enable occupational disease surveillance, though all have important shortcomings with regard to quality, comprehensiveness and accuracy. Important obstacles to improving occupational disease reporting include the lack of interest in prevention in health care, the inadequate training of health care practitioners in occupational health and the inherent conflicts between employers and workers in the recognition of work-related disease. Despite these factors, gains in occupational disease reporting and surveillance are likely to continue in the future.

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