Bakteri (jarang menyebabkan infeksi primer, tetapi bisa menyebabkan infeksi sekunder) Respiratory Viruses: Influenza A and B, respiratory syncytial virus (RSV), parainfluenza virus Mycoplasma pneumoniae, Streptococcus pneumonia, Haemophilus influenzae, Moraxella catarrhalis, Chlamydophila pneumoniae Bordetella pertussis