Hypersensitivity Pneumonitis

Hypersensitivity Pneumonitis: Common Features

  • Symptoms: Hypersensitivity pneumonitis (HP) presents acutely, as flu-like illness with cough; subacutely, as recurrent "pneumonia"; and chronically, as exertional dyspnea, productive cough and weight loss.

  • Signs: Most patients have abnormal imaging studies (chest x-ray or high-resolution CT). Crepitant rales are heard in some cases. Pulmonary function testing shows a restrictive defect in early disease and a restrictive, obstructive or mixed defect in late disease. Precipitating antibodies are neither sensitive nor specific, and their presence is no longer considered a hallmark of HP. Some patients have decreased diffusion capacity and arterial hypoxemia. If the diagnosis is in doubt, bronchoalveolar lavage typically shows lymphocytosis. Surgical lung biopsy may be indicated if bronchoscopy is nondiagnostic.

  • Latency: few weeks to years;

  • Onset of symptoms after acute exposure: 4 to 12 hours with resolution within a few days;

  • Repeated exposure to: 1) bioaerosols1 of microbial or animal antigens; or 2) a few reactive chemicals;

  • Resolution: improvement or complete recovery if exposure terminated early; otherwise, may progress to interstitial fibrosis;

  • Comments: The current definition of hypersensitivity pneumonitis includes many different diseases with many different etiologies: microbial agents, animal proteins, and chemical sensitizers. A common thread in the most common of these diseases is moldy organic matter or standing water in which potentially invasive2 microorganisms can grow and then become airborne particles in dust or mist. "The respirable conidia of Aspergillus species are ubiquitous in nature and commonly found in water, soil, and organic debris. A variety of Aspergillus species have been associated with HP in persons with diverse occupations, including soy sauce brewers, bird breeders, farmers, and compost, sawmill, mushroom, greenhouse, tobacco, cane mill, grain, and brewery workers, and in those exposed to contaminated esparto grass used in the production of ropes, canvas, sandals, mats, baskets, and paper paste." [Cecile S. Rose In: Murray, p. 1783] Forty-four cases of metalworking fluid HP occurring n ten different plants have been confirmed by lung biopsy. Concentrations of metalworking fluid aerosols in these plants were in most cases below the current OSHA standard. Recent studies have implicated Mycobacteria immunogenum, closely related to M. chelonae, as the causal agent. Improved engineering controls are needed to reduce exposure to metalworking fluids. [Rosenstock, p. 1043-54]


1 A bioaerosol is a suspension of particles of biologic origin in air, either a dust or a mist. 
2 Invasive diseases include aspergillosis caused by Aspergillis and mucormycosis, which is mainly caused by Rhizopus. [PPID, p. 3241-53, 3257-66]

Some of the Types, Antigens and Exposures that Have Been Identified
Disease Name Antigens Exposure
Bagassosis Bacteria (Thermophilic actinomycetes) Moldy bagasse (pressed sugarcane)
Mushroom worker lung Bacteria (Thermophilic actinomycetes) Mushroom compost
Metalworking fluids HP Bacteria (Mycobacterium immunogenum) Mist from metalworking fluids
Hot tub HP Bacteria (Mycobacterium avium complex) Mist from hot tubs
Lifeguard lung Bacteria (Endotoxin) Indoor swimming pool
Farmer's lung Bacteria (Thermophilic actinomycetes)
Fungus (Aspergillus species)
Moldy hay
Humidifier lung Bacteria (T. candidus, Bacillus subtilis, B. cereus, Klebsiella oxytoca)
Fungus (Aureobasidium pullulans )
Amoebae (Naegleria gruberi, Acanthamoeba polyhaga, Acanthamoeba castellani)
Mist from standing water
Compost HP Fungus (Aspergillus) Compost
Malt worker lung Fungus (Aspergillus clavatus) Moldy barley
Peat moss HP Fungi (Monocillium sp, Penicillium citreonigrum) Peat moss
Suberosis Fungus (Penicillum frequentans) Moldy cork dust
Maple bark HP Fungus (Cryptostroma corticale) Moldy wood bark
Wood pulp worker lung Fungus (Alternaria species) Moldy wood pulp
Wood trimmer lung Fungus (Rhizopus species) Moldy wood trimmings
Tree cutter lung Fungi (Penicillium (three species), Paecilomyces sp., Aspergillus niger, Aspergillus sp., Rhizopus sp.) Wood chips from living maple and oak trees
Dry rot HP Fungus (Merulius lacrymans) Moldy rotten wood
Sequoiosis Fungi (Graphium species, Pullularia species) Moldy wood dust
Japanese summer-type HP Fungus (Trichosporon cutaneum) Damp wood and mats
Cheese washer lung Fungus (Pencillum casei or P.roqueforti) Cheese casings
Tobacco worker lung Fungus (Aspergillus sp.) Moldy tobacco
Greenhouse HP Fungi (Aspergillus sp., Penicillium sp., Cryptostroma corticale) Moldy soil
Esparto grass HP Fungus (Aspergillus fumigatus) Moldy esparto used to produce ropes, canvas, sandals, mats, baskets, and paper paste;
Soy sauce brewer lung Fungus (Aspergillus oryzae) Fermentation starter for soy sauce
Bird breeder lung Avian proteins Bird droppings and feathers
Mollusc shell HP Aquatic animal proteins Mollusc shell dust
Animal handler lung Animal proteins Urine, serum, fur
Wheat weevil HP Wheat weevil (Sitophilus granarius) Infested flour
Silk production HP Silk worm larvae proteins Silk worm larvae
Isocyanate HP TDI, HDI, MDI Paints, resins, polyurethane foams
TMA HP Trimellitic anhydride Plastics, resins, paints

References: "Hypersensitivity Pneumonitis" by Cecile Rose in (Murray), "Hypersensitivity Pneumonitis and Organic Dust Toxic Syndromes" by Yvon Cormier and Mark Schuyler in (Asthma in the Workplace), Respiratory Illness in Workers Exposed to Metalworking Fluid Contaminated with Nontuberculous Mycobacteria --- Ohio, 2001, and Mycobacterial Aerosols and Respiratory Disease

See PubMed Abstacts on Hypersensitivity Pneumonitis

Revised May 30, 2018