Community-acquired pneumonia (CAP) is an acute infection of the pulmonary parenchyma that affects individuals outside of healthcare settings. It remains a leading cause of morbidity and mortality, especially among older adults and those with underlying health conditions. CAP is characterized by inflammation and consolidation of lung tissue due to the accumulation of white blood cells, fluid, and pus in the alveoli.

Diagnosis is based on clinical symptoms such as cough, fever, shortness of breath, and pleuritic chest pain, along with radiographic evidence of new lung infiltrates. The most common pathogens include bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae, as well as viruses like influenza, respiratory syncytial virus (RSV), and SARS-CoV-2. Fungal pathogens may also be involved in immunocompromised individuals.

Risk factors for CAP include advanced age, smoking, chronic diseases, and immunosuppression. Treatment typically involves antibiotics for bacterial infections, antivirals for viral causes, and supportive care with oxygen therapy and fluids. Preventive measures such as vaccination and smoking cessation play a crucial role in reducing the risk of CAP.