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Table 2 Classification and diagnostic criteria of hypersensitivity pneumonitis

From: Hypersensitivity pneumonitis: a complex lung disease

Characteristics Acute/subacute HP Chronic HP
Exposure to causal antigen Intermittent high-level exposure Continuous low-level exposure
Onset of symptoms 2–9 h after exposure; may evolve to gradually increasing symptoms over days to weeks Insidious, over weeks to months
Nature of symptoms Cough and dyspnea, but predominantly influenza-like symptoms Progressive symptoms (dyspnea, cough, and weight loss), sometimes punctuated by intermittent attacks of symptoms or slowly increasing
Physical signs Fever Inspiratory crackles; cyanosis; digital clubbing; cor pulmonale
Outcome Symptoms peak within 6–24 h after exposure, lasting hours to days. Symptoms recur on re-exposure and may progress to severe dyspnea End-stage fibrotic disease and/or emphysema. Exacerbations may occur despite avoidance of exposure
  1. Derived and adapted from the cluster analysis of the HP Study Group [3]