From the Guidelines
Streptococcus pneumoniae is the most common organism causing community-acquired pneumonia (CAP). This gram-positive, encapsulated diplococcus accounts for approximately 30-50% of all CAP cases where a pathogen is identified, as noted in the most recent study 1. S. pneumoniae typically colonizes the nasopharynx and can spread to the lower respiratory tract, causing infection when host defenses are compromised. The organism's virulence is largely attributed to its polysaccharide capsule, which helps it evade phagocytosis.
Other common CAP pathogens include:
- Haemophilus influenzae
- Mycoplasma pneumoniae
- Chlamydia pneumoniae
- Respiratory viruses
However, S. pneumoniae remains predominant across most patient populations and geographic regions, as supported by studies 1. Empiric antibiotic therapy for CAP typically includes coverage for S. pneumoniae, often with a beta-lactam (like amoxicillin or ceftriaxone) plus a macrolide (like azithromycin) or a respiratory fluoroquinolone (like levofloxacin) alone. Vaccination against S. pneumoniae is an important preventive measure, particularly for high-risk individuals such as the elderly and those with chronic medical conditions. The most recent study 1 emphasizes the importance of timely and adequate antibiotic coverage to decrease mortality and avoid drug resistance in CAP.
From the Research
Most Common Organism of Community-Acquired Pneumonia (CAP)
- The most common bacterial cause of CAP is Streptococcus pneumoniae (pneumococcus) 2, 3, 4, 5.
- Streptococcus pneumoniae remains the leading cause of CAP, although its incidence has declined, particularly in the US 5.
- Other common bacterial causes of CAP include Haemophilus influenzae, Staphylococcus aureus, and Gram-negative bacilli 4, 5.
- Viruses are also a significant cause of CAP, with respiratory viruses identified in about 30% of cases, and substantial rates of viral/bacterial coinfection 5.
- The incidence of CAP and its common complications are increasing, making it essential for physicians to have a good understanding of the management of CAP 6.