In the United States, death certificates are the primary source of information available to researchers for assessing cause(s) of death. Historically, there has been a lack of uniformity related to occupation and industry coding on death certificates between states. Because of differences in how information was recorded, aggregated analyses were often not possible. Therefore, early studies of mortality by occupation using death certificates were largely individual state-based efforts. In fact, a formal survey conducted in 1979 found that only six states coded industry and occupation and that there was no uniform coding system observed. To address this lack of uniformity in coding, a large collaborative initiative was launched in the 1980s between the National Institute for Occupational Safety and Health (NIOSH), the National Center for Health Statistics (NCHS), and other federal agencies and state health departments. This effort established a number of programs aimed at the standardization and routine recording of industry and occupation on death certificates (Figure 40–1). An initial governmental report was produced presenting the relative risks of mortality for selected causes of death by occupation and industry from 24 states (http://www.cdc.gov/niosh/pdfs/97-114.pdf). The success of that collaboration led to the ongoing National Occupational Mortality Surveillance System (NOMS) (http://www.cdc.gov/niosh/topics/surveillance/noms/). NOMS data are used to evaluate trends and identify potential risks for both acute and chronic disease mortality for industrial and occupational groups. Analyses and reports from NOMS are based on data from more than 11,000,000 death records for adults, age 18 and above, that died during the years 1984–1998 in 28 US states. More recently, data have been collected, coded, and analyzed for the years 1999, 2003–2004, and 2007–2010 from about 20 contributing states. The NOMS Web site will be updated periodically.
The National Occupational Respiratory Mortality System (NORMS) is a data storage and interactive data-retrieval system developed and maintained by NIOSH. NORMS is an extension of NOMS utilizing a compilation of national mortality data obtained annually from the NCHS multiple cause-of-death records for a number of respiratory conditions including malignant and nonmalignant workplace-associated diseases (http://webappa.cdc.gov/ords/norms.html). Currently, data from NORMS are presented in the NIOSH Work-Related Lung Disease Surveillance Report (WoRLD), which is an ongoing updated report available on the web. It presents mortality numbers and rates for all pneumoconiosis deaths by US geographic region (http://www2a.cdc.gov/drds/worldreportdata/).
It is important to note that there are many well-known limitations related to using death certificate data to assess temporal trends in mortality. Some of these include variability in reporting practices over time; revisions to the International Classification of Diseases (ICD) coding system; and the primary measure of effect, the proportionate mortality ratio, which does not directly derive mortality rates. However, there are many advantages in occupation-based mortality surveillance in the contemporary setting. The national vital statistics system has standardized the collection and reporting of death data. As electronic reporting has become more universally adopted, the quality and accessibility of the data have improved (http://www.cdc.gov/nchs/nvss/about_nvss.htm). These systems have been continually maintained and updated and are now largely available in up to date online reports.
The National Health Interview Survey (NHIS), conducted by CDC's National Center for Health Statistics (NCHS), is an ongoing cross-sectional household interview survey whose broad objective is to monitor the health of the US population. Interviews are conducted face-to-face in the homes of participants. With an annual sample size of over 100,000 and extensive demographic, health and lifestyle factors, NHIS has proven to be a valuable resource for understanding the health of the nation. Current and usual industry and occupation are coded in NHIS and the data are publicly available for analysis. NIOSH supplemented the NHIS to ask questions specific to work in 1988 and in 2010. Researchers have utilized NHIS data to assess employment-associated hearing loss, carpal tunnel syndrome, smoking prevalence, prevalence of short sleep duration, and work-related asthma. NHIS has also been utilized to assess lung cancer mortality by occupation as well as a variety of other occupational studies. Begun in 1957 in collaboration with the U.S. Census Bureau, NHIS is a large ongoing national survey that uses a complex multistage sampling strategy. Information regarding detailed study information as well as instructions for accessing NHIS data is available at http://www.cdc.gov/nchs/nhis.htm. Another occupational health supplement is planned for 2015.
The National Health and Nutrition Examination Survey (NHANES) is a program of studies of children and adults whose primary purpose is to assess the health and nutrition status of US residents. NHANES, run by NCHS, examines a nationally representative sample of about 5000 persons each year. The NHANES interview includes demographic, socioeconomic, dietary, and health-related questions. The examination component consists of medical, dental, and physiological measurements, as well as laboratory tests. Recent occupational studies using NHANES have found increased prevalence of hypertension among protective service workers, prevalence of airway obstruction by industry, physical activity patterns in relation to employment, and many others. From 2007 to 2012, questions related to exposures to pulmonary toxicants were included, and the population was evaluated for respiratory health status.
NHIS and NHANES are good sources for normative data for comparison purposes. It is often useful to use these sources as a benchmark in workplace investigations to evaluate elevated risk (http://www.cdc.gov/nchs/nhanes.htm).
Many state health and/or labor departments conduct surveillance for occupational illnesses. Data sources include the Behavioral Risk Factor Surveillance System (BRFSS), death certificates, cancer registries, hospital discharge data, workers' compensation systems, the Survey of Occupational Injuries and Illnesses (SOII), the Adult Blood Lead Epidemiology and Surveillance program (ABLES), and physician reports. For the past 25 years, NIOSH has provided technical and financial support to some states to establish or enhance state-based surveillance activities in occupational safety and health. As of 2010, 23 states receive funding. All collect at least 13 of 20 Occupational Health Indicators (OHIs), and 9 conduct enhanced surveillance and interventions in specific areas.
A. Occupational Health Indicators
The Council of State and Territorial Epidemiologists (CSTE) and NIOSH developed a set of indicators that states can use to evaluate the status of occupational health at a state level. These include measures of specific health outcomes, exposures, populations at risk, and resources to address occupational health challenges in the state. Details regarding these indicators can be found in Table 40–1, and at http://www.cste.org/group/OHIndicators.
Table 40–1.Occupational health indicators. ||Download (.pdf) Table 40–1. Occupational health indicators.
Nonfatal injuries reported by employers
Fatal work-related injuries
Amputations reported by employers
Amputations identified in state workers' compensation systems
Hospitalizations for work-related burns
Musculoskeletal disorders reported by employers
Carpal tunnel syndrome cases identified in state workers' compensation systems
Acute work-related pesticide poisonings reported to poison control centers
Incidence of malignant mesothelioma
Elevated blood lead levels among adults
Workers employed in industries with high risk for occupational morbidity
Workers employed in occupations with high risk for occupational morbidity
Workers in occupations with high risk of occupational mortality
Occupational health and safety professionals
OSHA enforcement activities
Workers' compensation awards
Hospitalizations for low-back disorders
The Behavioral Risk Factor Surveillance System (BRFSS) is a system of health surveys collected by states to assess health risk behaviors, preventive health practices, and health care access. Some modules collect information related to work and health, and the system has provided important insight on work-related asthma, depression and mental distress by occupation, lifetime risk of workplace eye injury, work-related noise-induced hearing loss, binge drinking by occupation and a variety of other health risk factors. An ongoing project supports the collection of industry and occupation as part of the survey in a number of states.
In each US state, medical facilities (including hospitals, physicians' offices, radiation facilities, surgical centers and pathology laboratories) are required to report incident cancers to a central cancer registry. Cancer registries manage information on all cancer cases and cancer deaths including the longest held occupation and industry of the patient. The CDC administers the National Program of Cancer Registries (NPCR), which supports central cancer registries in 45 states representing 96% of the US population (http://www.cdc.gov/cancer/npcr/).
Combined with the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, http://www.seer.cancer.gov/, incident cancer and cancer mortality statistics are collected for the entire US population. The CDC and NCI publish the comprehensive annual United States Cancer Statistics: Incidence and Mortality Report (http://apps.nccd.cdc.gov/uscs/), which currently includes incident data from registries covering 98% of the US population and mortality data for the entire United States.
State-based cancer registries monitor cancer trends over time and are fundamental to understanding the distribution of cancer in certain populations. These systems allow for identification of clusters of concern, the ability to assess cancer types by occupation and the ability to inform cancer control programs. In addition, intervention effectiveness can be assessed in comprehensive cancer registry programs.
D. Hospital Discharge Data
Hospitals typically maintain a diagnostic index or discharge summary that reflects the census of inpatients by presenting conditions for a particular period of time. In some cases, this information is aggregated for a broad geographic area to reflect the pattern of hospitalizations across institutions. Information from such sources serves as a valuable planning tool for within-institution resource allocation or for characterizing some between-institution differences. This information also may serve as an indicator or early-warning sign for health outcomes of special concern. It does not, however, provide a broad view of morbidity for the population of interest. For many conditions, discharge data tend to represent the extremes or episodes of illness severe enough to require hospital admission. This information also may include multiple case reports of the same individual with recurrent episodes of illness rather than a unique hospital discharge for each patient. Unique personal identifiers for each case may not be available owing to confidentiality issues. These data may better reflect the health care needs of a subgroup than the incidence or prevalence of diseases of interest.
E. Workers' Compensation Data
Worker's compensation systems are specific to each state. Designed to provide health benefits and wage-replacement for lost work-time, they are not designed as surveillance systems. They document acute injury and illness far more than chronic disease, which is rarely compensated. Case definitions and data elements vary across states, in addition to eligibility requirements. In 2012, NIOSH convened a workshop with other federal, state, and private organizations to consider how workers' compensation systems could contribute to efforts to understand the burden and risks for occupational injuries and illnesses (http://www.cdc.gov/NIOSH/docs/2013-147/pdfs/2013-147.pdf). In this review, it was noted that 11 states use these data for Occupational Health Indicators.
Mandated Reporting of Diseases by Clinicians & Laboratories
In many states, reporting of all or specific subsets of occupational diseases, injuries, and exposures is mandated for clinicians and/or laboratories. State-based reporting builds on the concept of occupational sentinel health events, i.e., “a disease, disability, or untimely death, which is occupationally related and whose occurrence may (1) provide the impetus for epidemiologic or industrial hygiene studies or (2) serve as a warning signal that materials substitution, engineering control, personal protection, or medical care may be required.” These systems are not meant to provide true counts of events, but rather to stimulate reporting, often among “sentinel providers” who develop expertise in the recognition and management of occupational illnesses. Such reports provide opportunities for follow-back with employers to identify workplaces at risk and emerging hazards. These systems are independent of workers' compensation systems. In fact, analyses of the overlap between physician reports and workers' compensation reports in some states demonstrate little overlap and provide opportunities to estimate the frequency of the conditions being partially reported into both systems.
A. Laboratory-Based Surveillance
Several states require laboratory reporting of agents such as arsenic, cadmium, lead, mercury, other metals, and carbon monoxide. Some monitor indicators of exposure to substances such as cholinesterase levels. Building on this requirement, the Adult Blood Epidemiology and Surveillance system (ABLES) is a state-based laboratory-reporting program to monitor and intervene on adult lead exposure in 41 states. The objective of the program is to reduce the rate of adults who have blood lead levels (BLL) of 10 mcg/dL or greater by targeting interventions to reduce exposures at work. Between 1994 and 2012, the program documented a 50% decrease in the national prevalence rates of BLL of 25 mcg/dL or greater. More information is available at http://www.cdc.gov/niosh/topics/ABLES/description.html.
B. Clinician-Based Reporting
Many states require reports of occupational illness or injury from clinicians who make such diagnoses. Conditions such as the pneumoconiosis (eg, asbestosis, coal workers' pneumoconiosis, silicosis), work-related asthma, musculoskeletal disorders, and pesticide toxicity are among those most commonly defined as reportable. Clinicians can find information on reporting cases at their state health department Web site. The Council of State and Territorial Epidemiologists (CSTE) maintains a Web site, which provides information on reporting requirements for all states and territories. This can be found at http://www.cste.org/group/SRCSQueryRes.
In addition, CSTE develops a list of nationally notifiable conditions. These conditions are reported from the states to the CDC to provide data at the national level. The list includes conditions classically considered occupational, such as silicosis and pesticide-related illness, as well as conditions such as hepatitis and anthrax, which are often associated with occupational exposures.
C. Intervention and Prevention
Surveillance systems must be tied to intervention activities to result in prevention of occupational illnesses. States have successfully used information generated through their surveillance systems to identify old hazards in new settings and emerging hazards. Examples include reduction of lead exposure to bridge workers, reduction of silica exposure among construction workers, heightened awareness of asthma risks associated with isocyanates used in new processes, among many.
Mandated Employer-Based Reporting Systems
Federal regulation (29 CFR Part 1904) requires the recording of all work-related fatalities and most work-related injuries and illnesses involving loss of consciousness, restricted work activity or job transfer, days away from work, or medical treatment beyond first aid. Most employers with more than 10 employees, and establishments not classified as a partially exempt industry must record work-related injuries and illnesses using OSHA Forms 300, 300A, and 301 (http://www.osha.gov/recordkeeping/RKforms.html). These reports include information regarding, where the event occurred, a description of the injury or illness, the number of days away from work and other demographic and health care related data. It is important to note that OSHA logs are maintained by the employer and are made available to OSHA upon request. OSHA logs are not publicly available information and mandated access is limited to OSHA, the Bureau of Labor Statistics (BLS) (in a modified form), employees, former employees, their personal representatives, and authorized employee representatives.
The annual Survey of Occupational Injuries and Illnesses (SOII) conducted by the BLS is an ongoing survey of between 170,000 and 180,000 US establishments in the United States. From its inception in 1973–2008, SOII surveyed private sector establishments only. In 2008, the public sector was added. The survey directs respondents to report injury and illness information directly from the OSHA logs. Injuries are more commonly reported than illnesses, and chronic diseases are rarely reported. In 2011, BLS reported 3.6 million nonfatal injuries compared to 208,000 illnesses (http://www.bls.gov/iif/oshsum.htm). The most common illnesses reported were skin diseases or disorders, respiratory conditions, poisonings, and hearing loss. Even for injuries, there is concern that the SOII substantially undercounts work-related events, and there is a concerted effort underway to improve the system. A government accountability office investigation conducted in 2009 revealed that enhancing OSHA's records audit process could improve the accuracy of worker injury and illness data (http://www.gao.gov/products/GAO-10-10).
For the mining industry, a parallel system is in place under a separate mandate and administered by the Mine Safety and Health Administration (MSHA). 30 CFR Part 50 requires that all accidents, injuries and illnesses occurring at a mining operation be documented on Form 7000-1 (http://www.msha.gov/forms/elawsforms/7000-1.htm) (Figure 40–2) and mailed to MSHA within 10 working days after an accident or occupational injury occurs or illness is diagnosed. The requirement of universal reporting of all work-related illnesses is a strength of this system. Annual reports by commodity are available from MSHA and access to the raw data is also publicly available (http://www.msha.gov/ACCINJ/accinj.htm). Although reporting of occupational illnesses and injuries is required by law, substantial underreporting has been documented.
MSHA form 7000-1. Mine accident, injury, and illness reporting form.
Epidemiology studies often provide the basis for occupational health surveillance systems to be developed and implemented. In addition, surveillance systems themselves can provide data that can be used in epidemiologic analyses. Some longitudinal studies of health behaviors, risk factors, medication and supplement use, and health outcomes have used occupational cohorts for convenience. These studies have followed physicians, nurses, teachers, and others. Other cohorts have been constructed because of perceived risk related to work, such as the Gulf long term follow-up study (GuLF Study) and the agricultural health study. This section will describe three large ongoing longitudinal health studies of occupational cohorts: the agricultural health study, the California teachers study and the GuLF study.
The agricultural health study is a prospective cohort of 89,656 pesticide applicators and their spouses recruited from Iowa and North Carolina. The study is jointly conducted by the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences (NIEHS) and the Environmental Protection Agency (EPA). The study comprises principally the main prospective cohort and assesses cancer and noncancer health outcomes through ongoing data collection. One facet of the study involves linkage to established disease surveillance systems including cancer registries, transplant registries, vital statistics and others. Cross-sectional studies have been conducted from the cohort and have included analyses of questionnaire data, biomarker studies and geospatial studies. Nested case-control studies, exposure studies and validation studies have also been pursued in the agricultural health study. This study has assessed numerous health outcomes among agricultural workers including neurologic risks, cancer risks, injuries and genetic associations. A comprehensive list of publications from this large cohort can be found online at http://aghealth.nci.nih.gov/study.html.
The California teachers study, originally funded by cigarette taxes for the support of breast cancer research, is a large prospective cohort of 133,479 female current and former teachers and administrators. The study began in 1995 and has tracked the morbidity and mortality of the inception cohort since that time. This study found significantly higher rates of breast cancer among teachers compared to other California women. The increased risk of breast cancer among teachers appears to be robust and has since been observed in Canadian school teachers. In addition to increased breast cancer risk, California school teachers also had higher rates of reproductive cancers including endometrial and ovarian as well as increased colon/rectum cancer compared to other California women. More recently, mortality data have become available from the California teacher cohort. The leading causes of death include ischemic heart disease, stroke, breast cancer and respiratory conditions including bronchitis/asthma and pneumonia/flu. The California teachers study has been invaluable in identifying potential health risks associated with teaching in public schools. A comprehensive list of publications from this large cohort can be found online at https://www.calteachersstudy.org/.
The GuLF study is the health study for workers involved with the cleanup of the Deepwater Horizon Gulf Oil Spill. In April of 2010, an explosion occurred on the deepwater horizon oil drilling rig leading to 11 fatalities and the release of an estimated 2.2 million gallons of crude oil into the Gulf of Mexico in the months that followed. During that time, temporary workers were deployed to clean up oil from beaches, coastline, and open water. At the peak of activity, there was an estimated 48,000 workers engaged in the response. The total number of workers involved over the course of the entire effort is unknown but likely exceeds 60,000. During the response, NIOSH developed a voluntary roster of response workers to create a record of those who participated in cleanup activities and a mechanism to contact them about possible work-related symptoms of illness or injury. The total number of workers rostered by NIOSH was 55,512. http://www.cdc.gov/niosh/topics/oilspillresponse/workerroster.html.
The roster information along with company records were given to NIEHS to conduct a long-term follow-up study of those involved with response to the spill. The aim is to prospectively follow the cohort of oil spill workers for long-term health effects of oil spill cleanup activities. A broad range of diseases will be examined. Study enrollment is ongoing as baseline data is being collected. The goal is to enroll 55,000 into the cohort. https://gulfstudy.nih.gov/en/index.html.
Large epidemiologic studies, particularly prospective cohort studies, are useful surveillance tools that can provide insights into occupational injuries and illnesses. They are especially useful for identifying risks of occupation-associated diseases of long latency and identifying risk factors of importance. Disease surveillance requires the systematic ongoing collection of health information. Epidemiology studies are often one of the more robust tools for accomplishing that purpose.