viral pneumonia

Viral pneumonia results from direct viral invasion of the respiratory epithelium and alveolar cells, causing interstitial inflammation rather than the alveolar consolidation typical of bacterial pneumonia. Common pathogens include influenza A/B, respiratory syncytial virus (RSV, especially in infants), parainfluenza, adenovirus, human metapneumovirus, and coronaviruses (including SARS-CoV-2). Pathophysiology involves epithelial cell necrosis, interstitial edema, and lymphocytic infiltration, which can impair gas exchange and predispose to secondary bacterial superinfection (classically Staphylococcus aureus or Streptococcus pneumoniae after influenza). Clinically, patients often have a preceding upper respiratory tract infection with gradual onset of fever, nonproductive cough, myalgias, and headache, in contrast to the abrupt onset and productive cough seen with bacterial pneumonia. Chest X-ray typically shows diffuse or patchy bilateral interstitial infiltrates rather than lobar consolidation. Lab findings often reveal normal or mildly elevated WBC count with lymphocytic predominance. Diagnosis is confirmed via PCR/antigen testing of respiratory secretions. Management is largely supportive, though antivirals (oseltamivir for influenza, ribavirin for RSV in select cases) may be used. Complications include ARDS, secondary bacterial pneumonia, and in immunocompromised hosts, more severe or disseminated disease. It's important to distinguish viral pneumonia from atypical bacterial pneumonia (Mycoplasma, Chlamydophila) and typical bacterial pneumonia both clinically and radiographically, as this affects treatment approach.