| Aetiology# | Cumulate incidence |
| Infectious aetiology | 97% of pulmonary infiltrates with diagnosis |
| Bacterial pneumonia¶ | 60% of pulmonary infiltrates of infectious aetiology |
| Streptococcus pneumoniae | 70% of bacterial pneumonia |
| Haemophilus influenzae | 10% of bacterial pneumonia |
| Staphylococcus aureus | 9% of bacterial pneumonia |
| Legionella pneumophila | 6% of bacterial pneumonia |
| Gram-negative bacillus | 5% of bacterial pneumonia |
| PCP | 20% of pulmonary infiltrates of infectious aetiology |
| Mycobacteriosis | 18% of pulmonary infiltrates of infectious aetiology |
| Mycobacterium tuberculosis | 80% of mycobacteriosis |
| Mycobacterium kansasii, MAC, Mycobacterium fortuitum and Mycobacterium xenopi | 20% of mycobacteriosis |
| Virus | 5% of pulmonary infiltrates of infectious aetiology |
| Cytomegalovirus | |
| Influenza virus | |
| Parainfluenza virus | |
| Respiratory syncytial virus | |
| Fungus | 2% of pulmonary infiltrates of infectious aetiology |
| Cryptococcus | |
| Aspergillus fumigatus | |
| Endemic fungal infections | |
| Parasite | 0.5% of pulmonary infiltrates of infectious aetiology |
| Toxoplasma gondii | |
| Strongyloides stercoralis | |
| Multiple organisms | 7% of pulmonary infiltrates of infectious aetiology |
| Other+ | 3% of pulmonary infiltrates of infectious aetiology |
| Noninfectious aetiology | 3% of pulmonary infiltrates with diagnosis |
| Pulmonary oedema | |
| Lung cancer | |
| Other |
PCP: Pneumocystis pneumonia; MAC: Mycobacterium avium complex. #: incidence of different aetiologies can vary in different geographical areas; ¶: percentage of each microorganism causing bacterial pneumonia is estimated among cases of bacterial pneumonia with identification of aetiology; +: bronchiectasis and pulmonary abscess. Data are based on results from [10, 11, 24].