Pneumonia: Symptoms, Causes, Treatment & When to Seek Care

Pneumonia is acute inflammation of the lung parenchyma (alveoli), typically infectious, causing airspace filling with exudate (fluid, pus, inflammatory cells) and impaired gas exchange.

Clinical Features

• Respiratory: Cough (productive – mucopurulent, rusty, blood-tinged), dyspnea, tachypnea, pleuritic chest pain.
• Systemic: Fever (may be absent in elderly), rigors, diaphoresis, fatigue, anorexia, myalgia, headache.
• GI: Nausea, vomiting, diarrhea (especially viral, Legionella, pediatric).
• Neurologic: Confusion, lethargy (elderly, severe sepsis – "altered mental status" is a CURB-65 criterion).

Etiology

• Community-acquired (CAP): S. pneumoniae #1; M. pneumoniae, C. pneumoniae, H. influenzae (atypical); viruses (flu, RSV, COVID); Legionella (water aerosols).
• Hospital-acquired (HAP) / Ventilator-associated (VAP): Gram-negatives (P. aeruginosa, Acinetobacter, Enterobacter), MRSA, resistant organisms.
• Aspiration: Anaerobes + aerobes (oral flora).
• Immunocompromised: P. jirovecii, fungi, CMV, TB, endemic mycoses.

Transmission

Respiratory droplets/aerosols (cough/sneeze/talk). Aspiration = endogenous. Not typically "caught" from environment except Legionella (water systems).

Diagnosis & Severity

• CXR: Consolidation, air bronchograms, effusion.
• Labs: CBC, CRP/PCT, BMP, LFTs, blood cultures (inpatient), sputum culture, urinary antigens, viral PCR.
• Severity scores: CURB-65, PSI, SMART-COP → outpatient vs. ward vs. ICU.

Treatment

• CAP Outpatient: Amoxicillin 1g TID or doxycycline 100mg BID × 5 days. Add macrolide if atypical suspicion.
• CAP Inpatient: Ceftriaxone + azithromycin (or levofloxacin/moxifloxacin monotherapy).
• HAP/VAP: Anti-pseudomonal β-lactam + anti-MRSA + aminoglycoside/fluoroquinolone per local antibiogram.
• Antivirals: Oseltamivir (flu), remdesivir/nirmatrelvir-ritonavir (COVID).
• Supportive: O₂, fluids, VTE prophylaxis, glycemic control, early mobilization.

Red Flags for Hospitalization

• Age > 65, comorbidities (COPD, HF, diabetes, immunosuppression)
• Hypoxia (SpO₂ < 92%), RR ≥ 30, hypotension, confusion
• Multilobar involvement, effusion, septic shock

Vaccines (pneumococcal, flu, COVID, RSV) are the most effective prevention.