Grain Dust-Induced Asthma

Grain dust induced asthma is occupational asthma from sensitisation to allergens in grain, flour and associated storage contaminants. Baker's asthma, from flour and enzyme additives, is the best defined form.

Exposure. Farming, grain handling, silo and elevator work, milling, baking, pasta and animal feed production.

Epidemiology. Baker's asthma is one of the commonest causes of occupational asthma in many countries. Dust levels and atopy raise risk.

Allergens. Wheat and rye flour proteins, alpha amylase and other enzymes, storage mites, weevils, moulds and endotoxin.

Related illness. Grain fever (organic dust toxic syndrome) is a distinct non-allergic febrile illness after heavy exposure. Chronic bronchitis and airflow obstruction also occur in grain workers.

Pathophysiology.

Cereal and enzyme proteins act as inhaled allergens, causing IgE-mediated early and late asthmatic responses.

Endotoxin and mould products enhance airway inflammation and produce neutrophilic bronchitis. Chronic exposure leads to airway remodelling.

• Cough, wheeze and dyspnoea related to work tasks, usually worse at work or in the evening, improved on days off.
• Rhinitis and conjunctivitis, often before asthma.
• Contact urticaria on hands in bakers.
• Grain fever causes fever, myalgia and malaise 4 to 8 hours after heavy exposure, resolving within 1 to 2 days.

Red flags.

• Severe attacks needing urgent care.
• Fever and dyspnoea persisting beyond 48 hours (hypersensitivity pneumonitis, infection).

• Work history including grain type, enzyme use, mould exposure and ventilation.
• Spirometry with reversibility, or methacholine challenge (PC20 under 8 mg/mL suggests asthma).
• Serial peak flow at least 4 times daily over at least 2 weeks at work and 2 weeks away.
• Skin prick tests or specific IgE to wheat, rye, alpha amylase, storage mites and moulds. These are more useful for baker's asthma than for other grain exposures.
• Specific inhalation challenge in a specialist centre when needed.

Differential diagnosis. Work exacerbated asthma, chronic obstructive pulmonary disease, hypersensitivity pneumonitis, organic dust toxic syndrome, irritant induced asthma, chronic bronchitis.

• Remove from exposure promptly; dust control, enclosure, local exhaust ventilation, and enzyme substitution or encapsulation in bakeries.
• Budesonide with formoterol 200/6 micrograms inhaled, 1 inhalation twice daily as maintenance plus 1 inhalation as needed (adults and adolescents 12 and over). Usual maximum 8 inhalations in 24 hours, up to 12 for a short period. Monitor symptoms, spirometry, exacerbations and oral candidiasis; rinse mouth after use. No renal adjustment; step up or down by control.
• Exacerbation: salbutamol 100 microgram metered dose through a spacer, 4 to 10 puffs, repeated every 20 minutes for the first hour, then every 4 hours as needed. Maximum 10 puffs each dose. Monitor heart rate, potassium and oxygen saturation. Caution in arrhythmia and hyperthyroidism.
• Exacerbation: prednisolone 40 to 50 mg orally once daily for 5 days, with no taper. Maximum 50 mg daily. Monitor glucose and blood pressure. Caution in diabetes and peptic ulcer; acceptable in pregnancy when needed; no renal adjustment.
• Grain fever: rest, fluids and paracetamol 1 g orally every 6 hours as needed, maximum 4 g in 24 hours (3 g if under 50 kg, chronic alcohol excess or liver disease), for 1 to 3 days. Reduce in hepatic impairment; extend interval when eGFR is under 30.

Monitoring. Review every 3 months initially with spirometry; annual surveillance in exposed workers.

Referral and escalation. Respiratory and occupational physician; workplace assessment; notification and compensation where required.

Special groups. Pregnancy: continue inhaled corticosteroid and avoid exposure.