Table 1.

Aetiology of hospitalised CAP in adults in Europe

Causative pathogen	Frequency (%)
Bacterial pathogens	0–47
Streptococcus pneumoniae	11–68
Haemophilus influenzae	5.3–12.3
Legionella pneumophilia	0–12.8
Staphylococcus aureus	0–11.8
Moraxella catarrhalis	0–5.4
Gram-negative bacteria	0–24.2
Mycoplasma pneumoniae	0.7–32.0
Chlamydia pneumoniae	1.0–26.5
Viruses	0–34
Influenza viruses	15–19
Rhinoviruses	0.7–12.0
Respiratory syncytial virus	3–4
Parainfluenza	3
Metapneumovirus	3
Adenoviruses	0.4–04
Bacterial–viral coinfection	31

The main causative organisms for CAP are listed, with frequency expressed as a percentage. Relative frequencies are pooled from multiple studies; some studies did not test for certain pathogens. Adapted from Welte and Köhnlein,⁴ Ewig et al ⁹ and Holter et al.¹⁰

CAP, community-acquired pneumonia.