CABP

CABP stands for community-acquired bacterial pneumonia, a form of pneumonia contracted outside hospital settings in which a bacterial pathogen is identified or presumed. It is distinguished from hospital-acquired pneumonia and other non-bacterial causes of pneumonia by its setting and typical pathogens.

The most common cause is Streptococcus pneumoniae. Other frequent bacteria include Haemophilus influenzae, Moraxella catarrhalis, and Staphylococcus aureus. Atypical bacteria such as Mycoplasma pneumoniae and Chlamydophila pneumoniae can also cause CABP and may present with less typical symptoms. Legionella species are less common but important in outbreaks.

Diagnosis relies on clinical features (cough, fever, dyspnea, pleuritic chest pain) and radiographic evidence of a new infiltrate. Sputum testing and blood cultures are not routinely required but may be performed in severe cases or when antibiotic resistance is a concern. Severity scores like CURB-65 or PSI guide site of care decisions, including whether to treat as an outpatient or admit to hospital.

Initial treatment is empirical and tailored to patient factors and local resistance; outpatient regimens include amoxicillin, doxycycline, or a macrolide in areas with low resistance. In patients with comorbidities or recent antibiotics, amoxicillin-clavulanate plus a macrolide or doxycycline, or a respiratory fluoroquinolone, may be used. Hospitalization is reserved for severe illness or high-risk patients, with a beta-lactam plus a macrolide or a respiratory fluoroquinolone.

Prognosis varies with age and comorbidities. Complications can include pleural effusion, empyema, bacteremia, and respiratory failure. Prevention includes vaccination against Streptococcus pneumoniae and annual influenza vaccination, plus measures such as smoking cessation and treatment of chronic conditions.