Hypersensitivity pneumonitis
Hypersensitivity pneumonitis is a fairly common occupational lung disease caused by molds in the workplace, e.g., Farmer's lung. Attacking fungal organisms set off an immune response resulting in lung inflammation. If the cause is not identified, acute episodes lead to a chronic lung disease.
CASES/YEAR
9,000 (US); 180,000 (Global)
OTHER NAMES
Extrinsic allergic alveolitis; Bagassosis; Mushroom worker lung; Metalworking fluids HP (Mycobacterium immunogenum); Hot tub HP (Mycobacterium avium complex); Lifeguard lung; Farmer's lung ; Humidifier lung; Compost HP; Malt worker lung; Peat moss HP; Suberosis; Maple bark HP; Wood pulp worker lung; Wood trimmer lung; Tree cutter lung; Dry rot HP; Sequoiosis; Japanese summer-type HP; Cheese washer lung; Tobacco worker lung; Greenhouse HP; Esparto grass HP; Soy sauce brewer lung; Bird breeder lung; Mollusc shell HP; Animal handler lung; Wheat weevil HP; Silk production HP;
INCUBATION
Weeks to years until "sensitized"; acute symptoms 4-12 hours after exposure;
INITIAL SYMPTOMS
Flu-like illness with respiratory symptoms;
COMMENTS
The findings in hypersensitivity pneumonitis depend on the stage of the illness. In the early stage, patients have acute episodes of a flu-like illness with cough. If exposure continues to occur over months and years, the patients will appear to be having recurrent pneumonia. Later, in the chronic stage, patients have exertional dyspnea, productive cough, and weight loss. Some patients have wheezing. Patients with hypersensitivity pneumonitis may have an abnormal chest x-ray and crepitant rales. Pulmonary function tests show a restrictive defect in early disease and a restrictive, obstructive, or mixed defect in late disease. The disease latency is anywhere from a few weeks to several years after the first exposure. Acute symptoms usually appear 4 to 12 hours after exposure to bioaerosols of microbial or animal antigens. Patients recover completely if the exposure is terminated early enough. Otherwise, the recurrent episodes lead to progressive interstitial fibrosis. [Harber, p. 201-211; Rom, p. 388-401] Patients exposed to mycobacterium avium complex (MAC) in pools and hot tubs may have abnormal chest x-rays (infiltrates or nodules). This form of HP may be a combination of early infection and hypersensitivity. [PPID 7th Ed., p. 3183]
DIAGNOSTIC
Clinical; Chest x-ray; Pulmonary function test; HRCT
SIGNS & SYMPTOMS
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>fatigue, weakness
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>fever
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>myalgia
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G nausea, vomiting
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H leukocytosis
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N headache
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R cough
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R dyspnea
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R sputum production
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R wheezing
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X lung infiltrates
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*pneumonitis
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*weight loss
SOURCE
Soil or Dust (Ingesting or Inhaling), Waterborne (Ingesting, Inhaling, or Swimming)
RESERVOIR
Birds and Poultry
RISK FACTORS
- Inhale bioaerosols indoors
- Inhale bioaerosols of moldy compost
- Inhale mists of metalworking fluids
- Inhale moldy hay, silage, or grain
- Inhale moldy wood dust
- Repeatedly inhale dust from birds
TREATMENT
No antimicrobial therapy;
REFERENCES FOR CASES/YEAR
1. (US) About 4% to 15% of interstitial lung disease cases are HP; The annual incidence of interstitial lung disease has been estimated at 30 per 100,000; [Lacasse2012: PMID 22796841] !0% of this rate = 3 per 100,000 as an estimated rate for HP; For the US 3 X 3000 = 9000;
2. (Global) 20 X US cases/yr;