The majority of cases of community acquired pneumomia are due to infection with-
Legionella pneumophila
Streptococcus pneumoniae
Haemophilus influenzae
Staphylococcus aureus
The most common infective agent of community acquired pneumonia is Streptococcus pneumoniae.Most cases are spread by droplet infection.Viral infections are impoant causes of CAP in children. Reference:Davidson's Medicine-22nd edition,page no:682
Respiratory system