THE CDC FIELD EPIDEMIOLOGY MANUAL

Occupational Disease And Injury

Kathleen Kreiss and Kristin J. Cummings

Introduction

For most adults and some teenagers, work accounts for at least one-third of the work week and half of waking hours. Work stress and work hazards constitute a public health burden that differs substantially from many public health responsibilities in the location of expertise and practice and in societal stakeholders. Even three centuries ago, Ramazzini described the maladies of particular occupations and called on physicians to always inquire about the nature of work in persons who consulted them for illness (1). Miners developed phthisis, now attributed to silicosis and mycobacterial disease to which they are rendered susceptible by silica dust’s toxicity to macrophages. Weavers developed asthma, now attributed to organic dusts contaminated with endotoxin. Mercury-exposed workers developed neurologic sequelae. Most public health workers believe that these workplace toxins are long-controlled, but old diseases crop up again in new industries, as a result of new technologies, or in the absence of regulation or enforcement. In addition, with the introduction of new exposures, new diseases are identified.

Identifying and Engaging Stakeholders

One of the first and most critical steps in conducting a field investigation of illness or injury in a workplace is identifying and engaging the stakeholders. The three basic stakeholder groups are workplace management, labor, and government.

Management

  • Small workplace. In a small workplace, the owner of the business may be the main contact for operations, health and safety issues, and human resources. Thus, this one person may be able to provide field epidemiologists with key information pertinent to the investigation, such as
    • A description of work processes.
    • Safety data sheets.
    • Recorded injury and illness data.
    • Employee rosters that include names, hire dates, departments, and job titles.
  • Workplaces operated by large companies. In contrast to small workplaces, workplaces operated by large regional or multinational companies may have entire departments dedicated to each function and personnel at the local, national, and international levels. In such situations, the epidemiologist needs to establish early in the investigation who will represent the management and serve as the main contact for investigators. Local-level managers are generally best informed about the workplace, and advocating for their involvement may be worthwhile. However, particularly in contentious situations (e.g., a worker death or severe illness or injury), local management may not be empowered to provide information or make decisions related to the investigation. It is not unusual for larger employers to refer public health investigators to an attorney.
  • Accessing workplaces and worker populations, and recognizing management concerns.
    • Management controls access to workplaces and on-site worker populations. Even with regulatory or statutory access for public health concerns, field epidemiologists benefit by developing trust with sensitivity to management concerns and clarity about public health procedures.
    • Economic concerns may derive from workers’ compensation claims or insurance rates. If a field investigation demonstrates product hazards, employers may encounter third-party lawsuits from workers in companies downstream that purchase a product. Even consumers of downstream company products may bring suit against the upstream manufacturer of a hazardous ingredient, as occurred in the manufacture of microwave popcorn with the butter flavoring diacetyl, which causes obliterative bronchiolitis (2).
    • Management may fear increased labor unrest and poor publicity.
    • Management also may be concerned about disclosure of proprietary business information and trade secrets, which can have economic ramifications.

Labor

  • Employees. Employees frequently are the stakeholder that brings concerns about workplace health and injury risks to public health attention. They might do this through consultation with physicians, who subsequently alert public health agencies, or through direct request. Confidentiality is important to most employees, who want to avoid being fired or disciplined for reporting to government authorities. Although legal protections exist for whistleblowers, access to legal representation may be limited by lack of familiarity and by economic constraints.
  • Labor unions. Historically, labor unions have been important stakeholders in requesting public health investigations. In 2017, just 6.5% of the US private sector workforce was represented by a labor union (3). When they represent employees, labor unions’ involvement in public health investigations is critical. They can provide an overview of the workplace and labor relations. International unions can leverage findings from an investigation across an industry by notifying local unions in other companies and by contract negotiations to include health and safety provisions, such as biological monitoring.
  • Contract labor. The use of contract labor has been growing for years. Employment arrangements, such as those involving both a contracting agency employer and a worksite employer, can complicate field investigations by introducing ambiguity about responsibility for workplace health and safety and workplace access. The National Institute for Occupational Safety and Health (NIOSH) of the Centers for Disease Control and Prevention has had experience with contracting agencies not allowing their employees to participate in public health investigations of the worksite employer. On the other hand, the California Department of Public Health required flavor manufacturers to include contract employees in monitoring for possible flavoring-related pulmonary function abnormalities (4). The field epidemiologist should explore the complexities of employment because contract employees may be at the highest risk for workplace injury and illness (5). The likelihood of success in an occupational investigation might increase if the public health investigator anticipates participation anxieties by labor stakeholders who might perceive their employment as increasingly precarious and fear plant closure or loss of a contingent labor contract.

Government

Government is a third stakeholder in occupational health and safety. The stake of government can be viewed as advancing the social contract that maintains a cohesive and productive society and enforcing laws and regulations. Occupational laws and regulations are national in scope and set by the federal government. The federal government delegates responsibility for their enforcement to some state agencies, which then have overlapping responsibilities in occupational health. At the federal level, relevant government roles are separated into two different departments: regulation/enforcement and research consultations/service.

  • Regulatory. In the US Department of Labor, the Occupational Safety and Health Administration (OSHA) and Mine Safety and Health Administration (MSHA) set and enforce workplace standards for exposures and safety in most workplaces. Under the General Duty Clause of the Occupational and Safety Health Act of 1970 (6), employers are required to provide their employees with a place of employment that “is free from recognizable hazards that are causing or likely to cause death or serious harm to employees.” In addition, these agencies have permissible exposure limits on a chemical-by-chemical basis. Permissible exposure limits exist for only a fraction of all potential workplace hazards and do not typically account for potential additive or synergistic properties of mixtures that might be present in workplaces. Thus, regulation has not eliminated many opportunities for hazardous exposures in the workplace (7).
  • Research and service. The primary federal government stakeholder pertinent to public health research and service investigation is NIOSH. NIOSH responsibilities encompass research to make recommendations for standards to guide OSHA and MSHA in setting regulations; investigative service to employees, industry, and state and local health departments; and education in occupational safety and health. In making recommended exposure limits to protect health, NIOSH is not required to consider cost or feasibility, but the regulatory agencies in the Department of Labor must consider those factors in setting permissible exposure limits. NIOSH’s role in recommending health-protective guidance for regulations makes NIOSH particularly interested in emerging, unregulated problems that warrant further investigation in workplaces or throughout an industry. In addition, NIOSH funds many state and local health departments to conduct surveillance of selected occupational health indicators, diseases, and injuries that are commonly reported without identifiers for national-level estimates of the burden of work-related disease.
Basic Operational Considerations in Recognizing and Investigating Occupational Diseases, Injuries, and Other Conditions

Approaches to recognizing and investigating occupational conditions can be readily distinguished from approaches to infectious disease. These differences especially pertain to initial recognition of the problem; types and availability of resources for investigations; need for quantitative exposure assessment; approaches to surveillance; and characterization and implications of differences in settings of exposure and occurrence.

Recognition

Public health agencies at local, state, and federal levels have mandated responsibilities and authorities to control both communicable and noncommunicable infections, and physicians are accustomed to regulations requiring reporting of many infections to state public health departments. In contrast, few physicians are trained to recognize work-related diseases, apart from infections. When state health departments have implemented reporting requirements for special surveillance efforts in occupational diseases or injuries, few physicians report (8). Nevertheless, occupational health has benefited from many astute physicians who have recognized or suspected new occupational diseases, such as bladder neuropathy resulting from a new catalyst in polyurethane foam manufacture (9), interstitial lung disease in nylon flock workers making upholstery (10), indium lung disease in workers making sputtering tiles for touch-sensitive screens (11), and obliterative bronchiolitis in microwave popcorn (12), flavoring (13), and coffee processing workers (14). When clinicians recognize possible occupational disease or injury, they commonly contact state or local public health agencies.

For many occupational diseases, physicians can treat patients without considering an occupational cause. For example, occupational asthma, which accounts for at least 15% of adult-onset asthma (15), could respond to pharmacologic treatment even though removal from the inciting workplace exposure early in the clinical course can result in permanent cure. Patients with carpal tunnel neuropathy may undergo surgery, when eliminating occupational repetitive motion of the wrist in nonneutral positions can relieve symptoms and progression. Such individual patients may be sentinels that co-workers sharing common exposures or physical stresses have similar health outcomes. Public health investigation of sentinel cases of suspected work-related injury or disease can result in remediation of causal factors and prevention of other cases.

Employees often recognize that a cluster of illness or injury exists among co-workers. Unless a physician serves a small geographic area or population, he or she is unlikely to suspect an association between several cases of a disease or chronic injury and a particular workplace.

Resources for Investigation

Upon receiving physician or employee reports of suspected work-related health outcomes, the field epidemiologist can try to ascertain whether the health problem results from a regulated exposure or work circumstance or from unregulated or unrecognized exposure or circumstances. For regulated exposures, OSHA or MSHA are appropriate resources. The regulatory agency can inspect the workplace to measure exposures and assess safety measures to prevent other cases by ensuring that standards are enforced. For example, lead poisoning in a lead-exposed worker can elicit corrective action from OSHA. Twenty-one states and one US territory have OSHA-approved state plans for enforcement that cover both private and local government workplaces, and five states and one territory cover only local government workers. In all other states, federal OSHA is responsible for investigation and enforcement. The potentially overlapping responsibility for occupational health and safety of state and federal government contrasts with most other public health responsibilities, which are state and local in authority, rather than federal.

Where standards for exposures do not exist, OSHA’s regulatory enforcement role is limited to the General Duty Clause (6). Examples of an unregulated hazard are repetitive motion injuries, frequently associated with force and rates of repetition, and indoor air– related complaints in damp buildings in which bioaerosol measurements that predict adverse health outcomes, such as asthma and hypersensitivity pneumonitis, do not exist. Obviously, emerging problems in the process of being recognized and investigated have no applicable regulations. An important responsibility of field epidemiologists is to investigate emerging occupational health problems and formulate exposure-control guidance. Investigation of known occupational diseases and other conditions in new settings also can have public health ramifications (Box 21.1) (16). Consultation with NIOSH or with academic centers that have occupational health expertise might be an efficient first step in contributing to the knowledge base of public health prevention of occupational diseases and injuries.

Box 21.1
Deaths in Fracking and Oil Workers

Public Health Problem

In 2010 and 2012, young workers in Montana and North Dakota died on catwalks while gauging fluid levels of crude oil and gas storage tanks.

Public Health Response

These possible sentinel events triggered review of media reports, OSHA case-fatality investigations, and the NIOSH Fatalities in Oil and Gas database. Seven similar nontraumatic deaths occurred during January 2010–March 2015 in three other states. Workers died while gauging or sampling tanks associated with concentrated sources of hydrocarbon gases and vapors in open air. Exposure assessment documented very low oxygen concentrations over open hatches and elevated hydrocarbon gas and vapor concentrations, which can cause acute central nervous system symptoms.

Take-Home Point

Sentinel event investigation can document new occupational hazards that can be prevented with alternative fluid sample collection points, remote monitoring of fluid levels, proper use of gas monitoring, and worker training.

__________
Source: Reference 16.

Quantitative Exposure Assessment

In contrast to most infectious disease investigations, quantitative exposure assessment is a priority in occupational health investigations. In attributing health outcome to working conditions, the level of exposure determines both the plausibility of an adverse health outcome and guidance for its control. Most epidemiologists will need to seek expert assistance from environmental scientists or industrial hygienists who have the training to determine levels of exposure in the workplace. Guidance for control of exposure depends on the exposure level and may include exhaust ventilation, other engineering controls, administrative controls, or personal protective equipment.

Field investigation of new occupational diseases or injuries often requires a cluster of cases that can be addressed in a workplace population– based manner. Exceptions are a work-related fatality and uncommon conditions known to have environmental causes, such as hypersensitivity pneumonitis. In most instances of a new disease, a single case cannot result in attribution to the workplace in the absence of an epidemiologic (population-based) approach to risk factors. Most emerging occupational diseases cannot be identified with a causal biomarker, such as blood lead level. For an actionable preventive outcome of investigating an emerging disease, clusters are usually necessary (Box 21.2) (2,1214,17).

Box 21.2
Obliterative Bronchiolitis in Flavoring-Exposed Microwave Popcorn Workers

Public Health Problem

Eight former microwave popcorn workers had severe lung disease; four were listed for lung transplantation.

Public Health Response

Review of medical records established a cluster of cases of fixed obstructive lung disease of unknown origin. The Missouri Department of Health and Social Services and NIOSH conducted a cross-sectional study of current workers, which demonstrated that 25% had spirometric abnormalities related in an exposure–response manner to exposure to diacetyl, the principal ingredient of artificial butter flavorings. Subsequent investigation of five other microwave popcorn workforces found cases consistent with obliterative bronchiolitis in four other factories.

Take-Home Point

An industrywide risk existed from diacetyl exposure, later implicated in cases in flavoring, cookie, and coffee production. Animal toxicology experiments provided biologic plausibility for risk assessment and recommended exposure limits.

__________
Source: References 2, 12–14, 17.

Surveillance

Surveillance is a long-standing public health tool to trigger field investigation. However, occupational disease and injury surveillance is rudimentary in comparison with infectious disease surveillance. In 1983, pioneers in occupational health surveillance (18) described 50 sentinel occupational health events that represented failures in prevention that should trigger public health action. The authors lamented that death certificates in many states did not have industry and occupation codes; although this remains true, some uniquely occupational diseases (e.g., pneumoconiosis) can be studied with death certificate surveillance. Many state health departments lack staffing to follow up on reported occupational diseases. Several states participating in NIOSH-funded sentinel event notification have contributed greatly to understanding certain conditions, including occupational asthma, silicosis, lead poisoning, and pesticide poisoning. In addition, the Council of State and Territorial Epidemiologists has developed recommendations for occupational health and injury surveillance (19), which many state health departments have adopted.

Other efforts involving occupational health surveillance are examination of workers’ compensation claims, which exist in each state; federally mandated surveillance of coal miners through submission of chest radiographs to NIOSH by physicians or clinics hired by coal mine operators; and supplemental federal surveillance of coal miners by NIOSH mobile teams visiting individual mines or regions to take chest radiographs and conduct pulmonary function tests. However, these unique programs for health surveillance of coal miners are not duplicated for other occupations and industries, for which health surveillance remains uncharacterized.

States with considerable initiatives in occupational health, such as California, Massachusetts, and Wisconsin, recently have contributed substantially to understanding new occupational health conditions. For example, the California Department of Public Health approached the emerging issue of flavoring-related obliterative bronchiolitis by partnering with California OSHA (CalOSHA) in a preventive program called the Flavoring Industry Safety and Health Evaluation Program. It required flavor manufacturers to report medical screening questionnaire and spirometry data on their employees to identify presumptive cases of flavoring-related lung disease (4). Employers were motivated to participate by assurance that CalOSHA would provide preventive consultation and not issue citations. Linking questionnaire and medical surveillance data on flavoring-exposed workforces also enabled characterization of risk factors (13,20). These risk factors, such as the annual amount of diacetyl used in production, reinforced the exposure–response relations found in a previous NIOSH investigation in Missouri (12). CalOSHA worked with the riskiest flavor workplaces to monitor implementation of respiratory protection and engineering controls.

Workplace Investigation

Clusters of suspected work-related disease and injury usually require access to employees in workplaces to conduct population-based epidemiology investigations. To identify risk factors that can guide preventive measures, field epidemiologists must establish common ground with employers, their lawyers, employees, and sometimes their union representatives. Usually the common ground is the desire to avoid harm to employees.

On-worksite collaboration with industrial hygienists or environmental scientists is nearly always required to plan and execute successful field investigations that examine the relation between environmental characteristics and evidence of ill health. Such collaboration is usually important in designing questionnaires for employees about job titles, work areas and practices, and potential work exposures by specific processes. Industrial hygienists measure exposure levels and observe work practices that allow estimation of exposure characteristics, such as average, peak, or episodic exposures. Such quantitative and qualitative evaluation is critical to investigating whether there are exposure– response relationships for adverse health effects found in questionnaire responses, biological indices, and physiologic tests administered by the health team. Thus, a workplace investigation usually involves a multidisciplinary team that requires space for confidential interviews and medical tests, requests for employees to wear personal exposure monitoring devices, and accommodation to production schedules. Good communication among team members and with management and workers is necessary for success in determining whether a workplace is safe for workers and what preventive interventions might be appropriate.

Part of communication with workplace stakeholders is the limits of any proposed investigation. For emerging occupational health problems, epidemiologic associations alone seldom establish the etiology. Newly recognized diseases or injuries trigger expectations that work-related health conditions should be compensated, exposures regulated, and surveillance instituted. These outcomes seldom result from field investigations alone. The contribution of field studies is to establish burden of health outcomes, exposure–response relations, temporality (e.g., by follow-up showing that exposure cessation interrupts the outbreak), and replicability among investigators and populations. Carefully designed field studies can contribute to the accumulation of evidence that workplace exposures are causally related to a new health problem. Effective field studies motivate experiments in laboratory settings to establish biologic plausibility of suspected causal agents, guidance for controlling exposures with engineering interventions and personal protective equipment, and medical and exposure surveillance to establish the effectiveness of interventions. Ultimately, these collective investigative efforts underlie the proposal of regulations to protect employees in diverse settings (2,21).

Challenges and Opportunities

Challenges

Occupational health poses several challenges for field epidemiology.

  • Exposure range and assessment. When a range of exposure does not exist, use of standardized questions can facilitate external comparisons to population-based data, such as the National Health and Nutrition Examination Survey or the Behavioral Risk Factor Surveillance System. Exposure assessment usually requires multidisciplinary access to a workplace with observational and measurement components. These aid in developing a workplace-specific questionnaire that includes information about tenure, job category, tasks or processes suspected to be risk factors, area or department of the workplace, and spills or mishaps. Exposure assessment usually is best informed by interdisciplinary collaboration regarding sentinel cases (including exploratory interviews) and review of company or OSHA exposure data before designing strategies for environmental sampling.
  • Misclassification of health outcome. New diseases found in a workforce may be misclassified as other diseases. For example, in the investigation of obliterative bronchiolitis associated with diacetyl exposure in a microwave popcorn factory, sentinel cases were diagnosed with asthma, emphysema, and bronchitis. Although field investigators found these sentinel cases more likely to have obliterative bronchiolitis, they did not consider current workers with abnormal restrictive spirometry to potentially have this occupational lung disease, another example of misclassification (2).
  • Healthy worker effect. Workers who become too ill to work or who recognize temporal relations of symptoms to aspects of the work environment might not stay in such work environments, as commonly is the case in occupational asthma clusters. This “healthy worker survivor effect” can result in underestimation of work-related disease when only the current workforce is studied, or it might obscure the exposures associated with disease onset when only current job is considered and miss persons who have transferred to another area to diminish work-related symptoms.
  • Management resistance. Management resistance to worker requests for public health assistance and access to workplaces for investigation can present additional challenges. Management might designate needed information as trade secret, might request investigators to sign confidentiality contracts, and might resist protection of worker confidentiality. Employers have considerable information about their employees, which enables presumptive identification of persons when aggregate results are stratified by race, sex, age group, tenure, or job category. NIOSH guidance for its field studies (called Health Hazard Evaluations) might be of interest to all field epidemiologists encountering workplace complaints (22).

Opportunities

Recognition and solving of occupational health concerns are underresourced (https://www.cdc.gov/niosh/oshworkforce/pdfs/NASHW_Final_Report-508.pdfpdf icon). Moreover, protective regulations about exposures and safety, even when they exist, may not be enforced because fewer than 1% of workplaces are inspected in a calendar year (7). Under these circumstances, field epidemiologists can play a critical role. Table 21.1 documents examples of past contributions of field epidemiologists to prevention and knowledge of new occupational risks (2,9–14,20,2330).

  • Identification of regulated hazards can trigger enforcement and follow-up by OSHA or MSHA. Beneficial effects can be immediate when causality is unquestioned or when lowering of exposure can be implemented by working with medical care providers and employers on appropriate restrictions of duty and guidance for intervention in workplaces.
  • Prevention of newly discovered disease associations across an industry usually depends on motivating others beyond the epidemiologic team to address causality. Guidance for interpreting epidemiologic associations as causal may depend on laboratory animal studies, replication in other workplaces and by other investigators, longitudinal follow-up to establish temporality, and establishment of exposure– response relations. These iterative efforts for emerging issues require other stakeholders to contribute to evidence that can be used in risk assessment to establish recommended or permissible exposure limits. Successful public health field investigations motivate efforts by other disciplines, agencies, and stakeholders and stimulate professional growth. Investigation involving industry partners can sometimes proceed to regulation proposed jointly by industry and labor.
  • Work-related public health opportunities might be more easily met with consultation from persons experienced in occupational health field investigations. Many NIOSH divisions have such expertise. Access is perhaps easiest by calling on those who conduct NIOSH Health Hazard Evaluations in the Respiratory Health Division or the Division of Hazard Evaluations, Surveillance, and Field Studies (https://www.cdc.gov/niosh/contact/officers.html). Those personnel can guide field epidemiologists through available resources, such as Safety Data Sheets for hazardous chemical products, known hazards associated with specific industries and occupations, and potential emerging problems that may benefit from collaborative investigation to leverage efforts in an understaffed public health agency.
Table 21.1
Selected occupational conditions identified by field epidemiologists
Condition Industry/activity Agent, when known
Occupational asthma Pesticide manufacture 3-amino-5-mercapto-1, 2, 4-triazole (23)
Hypersensitivity pneumonitis Leisure pool lifeguards Unspecified bioaerosols (24)
Obliterative bronchiolitis Microwave popcorn, flavoring, and cookie dough manufacture and processing of roasted and flavored coffee Diacetyl (2,3-butanedione) and related alpha diketones (2,12 14,20)
Pulmonary alveolar proteinosis, fibrosis, and emphysema Indium-tin oxide manufacture Indium, particularly sintered indiumtin oxide aerosols (11)
Obliterative bonchiolitis Fiberglass boat building and water tank manufacture Ingredients of plastic-coated resins, possibly styrene (25)
Lymphocytic bronchiolitis and peribronchiolitis Flocking of upholstery, greeting cards Nylon, rayon, and other synthetic respirable particles (10)
Asthma and hypersensitivity pneumonitis Damp indoor environments from structural water damage, contaminated air conditioning systems Bioaerosols (26)
Bladder neuropathy Polyurethane automobile seat manufacture Dimethylaminopropionitrile catalyst (9)
Color vision loss Windblade manufacture Styrene (27)
Tuberculosis Zoo with infected elephants Mycobacterium tuberculosis (28)
Carpal tunnel syndrome Poultry processing Repetitive motion (29)
Carbon monoxide poisoning Swimming around houseboats Carbon monoxide from generators (30)
Conclusion

Epidemiologists called on to conduct field investigations of occupational health and safety concerns have stimulating opportunities to explore associations of work conditions with adverse health outcomes, to intervene in preventing well-recognized occupational hazards, and to obtain expert consultation as needed. The challenges arising from diverse stakeholder interests at the heart of economic activity, from the need for environmental scientist involvement, and from deficits in surveillance and medical provider familiarity with occupational health concerns are at the forefront of public health development. Occupational health field epidemiology contributes to public health’s full potential in protecting our communities from the hazards of working life.

References
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  3. Bureau of Labor Statistics. News release. For release 10:00 a.m. (EST) Friday, January 19, 2018. Union members—2017. https://www.bls.gov/news.release/pdf/union2.pdf
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  19. Council of State and Territorial Epidemiologists. Occupational health indicators. http://www.cste.org/group/OHIndicators
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  22. National Institute for Occupational Safety and Health. Health hazard evaluation program. http://www.cdc.gov/niosh/docs/2009-167/
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  30. Centers for Disease Control and Prevention. Houseboat-associated carbon monoxide poisonings on Lake Powell—Arizona and Utah, 2000. MMWR. 2000:29:1105–8.