Alcoholics – Klebsiella, anaerobes usually due to aspiration (eg, Peptostreptococcus, Fusobacterium, Prevotella, Bacteroides)

IV drug users – S pneumoniae, S aureus

Aspiration – anaerobes

Atypical – Mycoplasma, Chlamydophila, Legionella, viruses (RSV, CMV, influenza, adenovirus)

Cystic fibrosis – Pseudomonas, S aureus, S pneumoniae, Burkholderia cepacia

Immunocompromised – Pneumocystis jirovecii (with HIV), S aureus, enteric gram Θ rods, fungi, viruses

Nosocomial – S aureus, Pseudomonas, other enteric gram Θ rods

Postviral – S pneumoniae, S aureus, H influenzae