Coronavirus Disease 2019 (COVID-19)

Definition

COVID-19 is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), primarily affecting the respiratory system but potentially involving multiple organ systems.

Epidemiology

• First identified in Wuhan, China, in December 2019
• Spread globally, resulting in a pandemic
• Affects all age groups, with higher severity in older adults and those with comorbidities
• Transmission occurs mainly via respiratory droplets, aerosols, and contact with contaminated surfaces
• Asymptomatic cases are common, contributing to widespread transmission

Etiology

• Caused by SARS-CoV-2, an enveloped, positive-sense single-stranded RNA virus
• Virus enters host cells via ACE2 receptors in respiratory epithelium
• Variants with mutations in spike protein affect transmissibility and immune escape
• Predisposing factors for severe disease include age >65, diabetes, cardiovascular disease, chronic lung disease, obesity, and immunosuppression

Pathophysiology

• Viral entry via ACE2 receptors in respiratory epithelium
• Viral replication triggers immune response and inflammation
• Cytokine storm in severe cases leads to acute respiratory distress syndrome (ARDS)
• Endothelial injury, microthrombosis, and multi-organ involvement can occur
• Diffuse alveolar damage leads to impaired gas exchange
• Hypercoagulable state increases risk of thromboembolic events
• Recovery involves immune-mediated viral clearance and tissue repair