Hypersensitivity Pneumonitis Is Rising While Other Occupational Lung Diseases Decline: What Employers Need to Know

A new study published in the American Journal of Respiratory and Critical Care Medicine in May 2026 has revealed a striking divergence in occupational lung disease mortality trends in the United States. While deaths from traditional occupational respiratory diseases — silicosis, asbestosis, and coal workers' pneumoconiosis — have declined significantly over the past two decades, hypersensitivity pneumonitis (HP) is the only occupational lung disease with a rising mortality rate.

For employers, this finding signals that workplace respiratory hazards are evolving. The exposures that cause HP — mold, contaminated metalworking fluids, organic dusts, and certain chemicals — are present across a wide range of industries. As traditional dust-related diseases recede thanks to decades of regulation and enforcement, a new generation of respiratory threats demands attention.

What the Research Shows

The study analyzed CDC WONDER death certificate data for U.S. adults aged 55 and older from 1999 to 2023, identifying 20,242 deaths attributed to occupational lung diseases during this period. The findings paint a clear picture of shifting risk:

Declining Diseases

• Coal workers' pneumoconiosis (black lung): Age-adjusted mortality rate fell from 0.73 to 0.16 per 100,000 — a decline of 7.5% per year
• Asbestosis: Dropped from 0.75 to 0.27 per 100,000 — declining 4.10% annually
• Silicosis: Decreased from 0.15 to 0.03 per 100,000 — a 4.64% annual decline

The Exception: Hypersensitivity Pneumonitis

• HP mortality rose from 0.06 to 0.22 per 100,000 between 1999 and 2023
• The annual percent change was +7.74% — a statistically significant increase
• The highest mortality rates were observed in the West and Midwest regions
• Older adults (55+) were most affected

All trends were statistically significant (p < 0.05). The declines in traditional occupational lung diseases reflect the success of decades of regulatory standards, enforcement actions, and workplace controls. But the rise in HP mortality suggests that newer or less-recognized workplace exposures are creating a growing health burden.

Understanding Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis is an immune-mediated inflammatory lung disease triggered by repeated inhalation of specific environmental antigens. Unlike dust-deposit diseases such as silicosis, HP results from an exaggerated immune response to inhaled particles — meaning even relatively low concentrations of certain substances can cause disease in susceptible individuals.

Common Occupational Forms

Form	Exposure Source	Typical Industries
Farmer's lung	Moldy hay, grain, compost	Agriculture, animal husbandry
Machine operator's lung	Contaminated metalworking fluids	Manufacturing, machining
Chemical worker's lung	Isocyanates, reactive chemicals	Automotive, construction, foam production
Mushroom worker's lung	Mushroom compost	Food production
Humidifier/HVAC lung	Contaminated water systems	Office buildings, any indoor workplace

Why HP May Be Increasing

Researchers and occupational health experts point to several possible factors driving the increase:

1. Evolving workplace environments: Growth in industries that use metalworking fluids, spray applications, and synthetic chemicals may be increasing exposure opportunities
2. Building-related exposures: Poor HVAC maintenance and water damage in commercial and industrial buildings can create mold and bacterial reservoirs that expose large numbers of workers
3. Improved diagnosis: Greater awareness and better diagnostic imaging (high-resolution CT scans) may be identifying cases that were previously missed or misclassified
4. Climate factors: Increasing humidity and temperature in some regions may promote mold growth in agricultural and indoor settings

The Regulatory Landscape

Unlike silica and asbestos, there is no OSHA permissible exposure limit (PEL) specific to the biological and chemical agents that cause HP. However, employers still have clear legal obligations:

OSHA's General Duty Clause

Under Section 5(a)(1) of the OSH Act, employers must provide a workplace "free from recognized hazards that are causing or are likely to cause death or serious physical harm." If HP-causing exposures are present and recognized in an industry, OSHA can cite employers under this provision.

Respiratory Protection Standard (29 CFR 1910.134)

When engineering controls cannot adequately reduce airborne exposures, employers must implement a respiratory protection program that includes:

• Hazard assessment and respirator selection
• Medical evaluations for respirator use
• Fit testing
• Training on proper use and maintenance
• Written program documentation

OSHA Recommendations for Preventing Respiratory Illness

OSHA's general recommendations to prevent respiratory illnesses in the workplace emphasize:

• Identifying and assessing airborne hazards
• Implementing engineering controls as the primary defense
• Using administrative controls to limit exposure duration
• Providing appropriate PPE when other controls are insufficient
• Conducting worker health surveillance

NIOSH Surveillance and Research

NIOSH's Respiratory Health Program conducts ongoing surveillance of occupational lung diseases, including HP. Their work helps identify emerging trends, develop prevention strategies, and inform OSHA rulemaking. The NIOSH Occupational Respiratory Disease Surveillance system tracks mortality and morbidity data that enables studies like the one published this month.

What Employers Should Do

The rising trend in HP mortality is a call to action for employers across multiple industries. Here are concrete steps to protect your workforce:

1. Identify and Assess Exposure Sources

• Audit your workplace for potential HP-causing agents: mold, metalworking fluids, organic dusts, isocyanates, animal proteins, and microbial contaminants
• Inspect HVAC systems for water damage, stagnant water, and microbial contamination
• Review metalworking fluid management — contaminated fluids are a leading cause of occupational HP in manufacturing
• Assess agricultural operations for mold exposure during handling of hay, grain, and compost

2. Implement Engineering Controls

• Install and maintain local exhaust ventilation at points where aerosols or dusts are generated
• Ensure HVAC systems are properly designed, maintained, and cleaned on a regular schedule
• Use enclosed or automated processes where feasible to limit direct worker contact with antigens
• Implement metalworking fluid management programs that include regular testing, filtration, and replacement schedules

3. Establish a Respiratory Protection Program

• Comply with 29 CFR 1910.134 requirements
• Provide NIOSH-approved respirators (N95 or higher) for workers in high-risk environments
• Conduct medical evaluations and fit testing
• Train workers on proper respirator use, storage, and limitations

4. Train Workers to Recognize Early Symptoms

Educate employees about the signs of HP, which often mimic flu or pneumonia:

• Shortness of breath, especially with exertion
• Dry cough
• Fever and chills (typically 4–8 hours after exposure)
• Fatigue and malaise
• Weight loss (in chronic cases)

Early recognition and removal from exposure are critical — continued exposure can lead to irreversible lung fibrosis.

5. Implement Health Surveillance

• Conduct baseline and periodic pulmonary function testing for workers in high-risk roles
• Use symptom questionnaires to identify early respiratory complaints
• Investigate any clusters of respiratory illness promptly
• Maintain medical records in compliance with OSHA recordkeeping requirements (29 CFR Part 1904)

6. Act Immediately When Cases Are Suspected

• Remove the affected worker from exposure pending medical evaluation
• Investigate the workplace to identify the exposure source
• Report work-related respiratory illnesses per OSHA requirements
• Consult an occupational medicine specialist for diagnosis and return-to-work guidance

Industries at Highest Risk

Based on the epidemiological data and known exposure pathways, employers in the following sectors should be especially vigilant:

• Agriculture: Grain elevators, dairy operations, poultry farms, mushroom cultivation
• Manufacturing: Metalworking, machining, plastics, foam and polyurethane production
• Food processing: Brewing, baking, cheese-making, mushroom processing
• Woodworking: Sawmills, lumber yards, furniture manufacturing
• Healthcare and laboratory settings: Animal handlers, research facilities
• Office and commercial buildings: Any facility with poorly maintained HVAC, water damage, or visible mold

Connecting the Dots: A Broader Occupational Health Strategy

The rise in HP mortality underscores a broader lesson for occupational health professionals: as traditional hazards are controlled, new and evolving exposures emerge. Employers who take a comprehensive approach to respiratory health — rather than focusing solely on regulated substances — will be better positioned to protect their workforce.

This aligns with NIOSH's Total Worker Health framework, which encourages employers to integrate safety protection with health promotion. A proactive respiratory health program that includes hazard identification, exposure monitoring, health surveillance, and early intervention serves as a model for addressing both legacy and emerging occupational health threats.

For employers looking to understand the broader 2026 compliance landscape, BlueHive's 2026 Occupational Health Compliance Timeline and Checklist provides a practical guide to regulatory milestones and employer responsibilities throughout the year.

Looking Ahead

The 2026 study findings will likely prompt increased attention from federal agencies. NIOSH has already signaled its focus on emerging respiratory hazards through expanded surveillance programs, and occupational health researchers are calling for updated exposure guidelines for biological agents associated with HP.

Employers who act now — before regulatory requirements catch up to the science — will not only protect their workers but also position themselves ahead of potential future enforcement actions. The lesson from silica and asbestos enforcement is clear: early investment in prevention is always less costly than reactive compliance after workers become ill.

Sources

• Occupational Lung Disease Mortality in the U.S., 1999–2023 — American Journal of Respiratory and Critical Care Medicine (2026)
• CDC WONDER — Wide-ranging Online Data for Epidemiologic Research
• NIOSH Respiratory Health Program — CDC
• NIOSH Occupational Respiratory Disease Surveillance — CDC
• OSHA Respiratory Protection Standard — 29 CFR 1910.134
• OSHA Recommendations to Prevent Respiratory Illnesses in the Workplace
• OSHA Recordkeeping Requirements — 29 CFR Part 1904
• NIOSH Total Worker Health Program — CDC
• 2026 Occupational Health Compliance Timeline and Checklist — BlueHive