This organism is commonly seen in smokers who get pneumonia.

• A. Moraxella catarrhalis
• B. Mycoplasma pneumoniae
• C. Haemophilus influenzae
• D. Streptococcus pneumoniae

Answer: (C)

Smoking impairs mucociliary clearance and local airway defenses, making the lungs more susceptible to infection by Haemophilus influenzae. In adults with COPD or a history of smoking, non-typeable Haemophilus influenzae is a common cause of pneumonia because these strains lack a capsule and readily colonize inflamed airways. They prefer the respiratory tract environment created by smoking and COPD, leading to lower respiratory infections. This contrasts with Mycoplasma pneumoniae, which more often causes atypical pneumonia in younger adults, and with encapsulated strains of H. influenzae (type b), which are more associated with invasive disease in children. Thus, the association between smoking and H. influenzae as a cause of pneumonia makes it the most fitting answer.