Hypersensitivity Bronchitis

Inflammation of the larger and smaller airways caused by an immune reaction to inhaled organic or chemical antigens, producing chronic cough, sputum and airflow limitation without the diffuse alveolar inflammation of hypersensitivity pneumonitis.

• Antigens: mould spores and bioaerosols (farming, hay, grain, silage, mushroom compost), animal and avian proteins, endotoxin, cotton and flax dust, isocyanates, acid anhydrides, metalworking fluids, humidifier and air conditioner water, wood dust and enzymes.
• Burden: it is an under-recognised occupational and domestic cause of chronic bronchitis; farm workers have chronic bronchitis in about 10 to 20%.
• Mechanism: type III and IV immune reactions with neutrophilic and lymphocytic inflammation of the bronchial wall, goblet cell hyperplasia, mucus hypersecretion and mucociliary dysfunction.

Cough with sputum for more than 3 months in a year, wheeze, chest tightness, mild dyspnoea; often worse during or after a working shift and better on weekends and holidays.

• Acute flu-like episodes with fever and malaise 4 to 8 hours after heavy exposure.
• Examination: wheeze or coarse crackles; usually no clubbing or basal fine crackles (those suggest pneumonitis).
• History of symptoms in a specific environment (barn, mushroom farm, cotton mill, bird keeping, damp house, humidifier).
• Differential diagnosis: occupational asthma, hypersensitivity pneumonitis, chronic obstructive pulmonary disease, smoker's bronchitis, bronchiectasis, tuberculosis, reflux cough, upper airway cough syndrome, allergic bronchopulmonary aspergillosis.
• Complications: chronic airflow obstruction, progression to hypersensitivity pneumonitis, recurrent infection, bronchiectasis, and loss of work.

Spirometry before and after a work shift or exposure (fall in FEV1 of 10% or more), and with bronchodilator reversibility.

• Serial peak expiratory flow, at least 4 times daily for 3 weeks at work and 2 weeks away (a work related fall of 20% or more in variability supports the diagnosis); methacholine challenge if spirometry is normal.
• Serum specific IgG precipitins to suspected antigens (supportive; also positive in exposed unaffected people).
• Chest X-ray, and high-resolution CT (normal, or bronchial wall thickening and mosaic attenuation; ground glass, centrilobular nodules and air trapping suggest hypersensitivity pneumonitis).
• Induced sputum (neutrophil or lymphocyte excess), blood eosinophils, total IgE, skin prick tests, full blood count.
• Bronchoalveolar lavage (lymphocytes more than 30% suggests pneumonitis) when imaging is abnormal; exposure history using a structured questionnaire and workplace survey.

Exposure control is the key treatment: avoid or reduce the antigen (change job duties or workplace, remove sources of mould and damp, clean or stop humidifiers, remove birds), with a respirator (FFP3 mask) in unavoidable exposure, and ventilation and wet handling of materials.

• Stop smoking: varenicline 0.5 mg once daily for days 1 to 3, 0.5 mg twice daily for days 4 to 7, then 1 mg twice daily for 12 weeks; nicotine patch 21 mg/24 hours for 6 weeks, then 14 mg for 2 weeks and 7 mg for 2 weeks.
• Inhaled corticosteroid: budesonide 400 micrograms twice daily or fluticasone propionate 250 micrograms twice daily for at least 3 months, reduced to the lowest effective dose; with a long-acting beta agonist (formoterol 12 micrograms twice daily or salmeterol 50 micrograms twice daily, always combined with the corticosteroid).
• Long-acting antimuscarinic: tiotropium 18 micrograms once daily inhaled when airflow obstruction persists.
• Reliever: salbutamol 100 micrograms 1 to 2 puffs as needed.
• Acute exacerbation after heavy exposure: prednisolone 30 to 40 mg daily for 5 to 7 days (no taper needed).
• Mucus clearance: hypertonic saline 3% to 7% 4 mL nebulised twice daily after salbutamol, active cycle of breathing technique, and carbocisteine 750 mg three times daily if sputum is thick.
• Antibiotics only for purulent exacerbations with fever: amoxicillin 500 mg three times daily for 5 days, or doxycycline 200 mg then 100 mg daily for 5 days.
• If progressive or fibrotic disease develops, give prednisolone 0.5 mg/kg daily for 4 to 6 weeks, then taper over 3 to 6 months, with mycophenolate 500 mg twice daily increased to 1 g twice daily or azathioprine 1 to 2 mg/kg daily (evidence limited).
• Special groups: children (domestic antigens, animals, damp; avoid sources, paediatric inhaled corticosteroid dosing); pregnancy (inhaled corticosteroids and salbutamol are safe, avoid isocyanate exposure); elderly (check inhaler technique and consider spacer); occupational disease (notify, support compensation, fit-for-work reassessment); renal impairment (no changes).
• Red flags: breathlessness out of proportion, weight loss, fine basal crackles, clubbing, hypoxaemia, fibrosis on CT, haemoptysis.
• Follow-up: review at 4 to 6 weeks with spirometry and peak flow, then every 3 months for a year; repeat CT at 6 to 12 months if the first scan was abnormal; annual spirometry while exposed.