| Infection (8–10%) | Viral infection (eg. cytomegalovirus infection, infection with Epstein–Barr virus) |
| Bacterial infection (eg. Pertussis, Legionella, Mycoplasma, Chlamydia, or Mycobacterium species) |
| Fungal infection (eg. infection due to Histoplasma, Aspergillus or Pneumocystis species) |
| Parasitic infection (eg. visceral larva migrans) |
| Environmental conditions (13%) | Exposure to organic dusts (hypersensitivity pneumonitis [7–12%]) |
| Exposure to inorganic particulates (eg. silica, asbestos, talc, zinc) |
| Exposure to chemical fumes, gases |
| Drugs | Antineoplastic agents |
| Other drugs or elements (eg. penicillamine, nitrofurantoin, gold) |
| Previous lung injuries | |
| Chronic aspiration pneumonitis (4%–5%) | |
| Resolving acute respiratory distress syndrome | |
| Bronchopulmonary dysplasia | |
| Lymphoproliferative disorders (10%) | |
| Metabolic disorders | |
| Lysosomal storage disorders (eg. Gaucher disease, Niemann–Pick disease) |
| Degenerative disorders (eg. pulmonary microlithiasis [1%]) |
| Immunodeficiency-associated ILD |
| Disorders with unknown causes |
| Undetermined (19–27%) |
| Pulmonary haemorrhage syndromes |
| Desquamative interstitial pneumonia (4–8%) |
| Lymphocytic interstitial pneumonitis (6%) |
| Lymphangiomatosis (4%) |
| Nonadenoviral bronchiolitis obliterans (4%) |
| Sarcoidosis (2%) |
| Pulmonary alveolar proteinosis (2%) |
| Eosinophilic syndromes (2%) |
| Idiopathic bronchiolitis obliterans organizing pneumonia (BOOP) |
| Bronchocentric granulomatosis (1%) |
| Nonspecific interstitial pneumonia (correlates with ABCA3 deficiency) |
| Acute interstitial pneumonitis |
| ILDs associated with systemic diseases |
| Connective tissue diseases (2–4%) (juvenile rheumatoid arthritis, dermatomyositis/polymyositis, systemic sclerosis, systemic lupus erythematosus, ankylosing spondylitis, Sjögren syndrome, Behçet syndrome, mixed connective tissue disease) |
| Autoimmune diseases (anti-glomerular basement membrane antibody disease) |
| Pulmonary vasculitis |
| Liver disease (chronic active hepatitis, primary biliary cirrhosis) |
| Bowel disease (2%) (eg. ulcerative colitis, Crohn’s disease) |
| Amyloidosis |
| Neurocutaneous disorders (tuberous sclerosis, neurofibromatosis, ataxia–telangiectasia) |
| Bronchiolitis obliterans |
