Pneumonias

Pneumonias are infections of the lung parenchyma that cause inflammation and consolidation in the affected areas. They result from a variety of organisms, including bacteria, viruses, fungi, and, less commonly, parasites. In adults, bacterial causes are common, with Streptococcus pneumoniae accounting for a large share, along with Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, and atypical pathogens such as Mycoplasma pneumoniae and Chlamydophila pneumoniae. Viral pneumonias frequently involve influenza, respiratory syncytial virus, and SARS-CoV-2. Fungal pneumonias are more likely in people with immune suppression or certain exposures (eg, Pneumocystis jirovecii, histoplasma).

Clinical presentation varies but typically includes cough, fever, dyspnea, chest pain, and sputum production. Older adults may present with confusion or functional decline rather than classic symptoms. Risk factors include advanced age, chronic lung disease, cigarette smoking, immune suppression, and recent hospitalization.

Diagnosis relies on clinical assessment reinforced by imaging and laboratory testing. Chest radiography or computed tomography can show focal consolidation or interstitial patterns. Microbiological testing may include sputum Gram stain and culture, blood cultures, respiratory viral panels, and molecular assays to identify pathogens.

Classification commonly distinguishes community-acquired pneumonia, healthcare-associated or hospital-acquired pneumonia, and ventilator-associated pneumonia. Treatment is etiologically guided but often begins with empiric antibiotics for community-acquired pneumonia and broader coverage for hospital-acquired cases. Preventive measures include vaccination against pneumococcus and influenza, smoking cessation, and infection control practices. Prognosis ranges from full recovery with appropriate treatment to severe illness and death, particularly among older individuals and those with comorbidities.