COVID-19

Introduction

COVID-19 is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first identified in Wuhan, China, in December 2019. It quickly spread globally, leading to the World Health Organization (WHO) declaring a pandemic on March 11, 2020.

COVID-19 primarily affects the respiratory system but is now recognized as a multisystem disease with acute and long-term complications. Clinical severity ranges from asymptomatic infection to critical illness with respiratory failure, multi-organ dysfunction, and death.

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Epidemiology

• Over 700 million confirmed cases and more than 7 million deaths globally (WHO, 2024 data).

• Mortality highest in elderly adults, those with comorbidities (diabetes, hypertension, obesity, heart disease, cancer), and immunocompromised patients.

• Transmission is mainly via respiratory droplets, aerosols, and contaminated surfaces (fomites).

• Variants of concern (e.g., Alpha, Delta, Omicron) have influenced transmission, disease severity, and vaccine effectiveness.

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Etiology and Pathophysiology

1. SARS-CoV-2 Virus

• Belongs to the coronavirus family, an enveloped, positive-sense, single-stranded RNA virus.

• Uses spike (S) protein to bind to the ACE2 receptor on host cells (lungs, heart, kidneys, GI tract, endothelial cells).

2. Pathogenesis

• Viral entry → replication in respiratory epithelium.

• Local inflammation and cytokine release.

• Severe cases: cytokine storm with excessive immune activation (IL-6, TNF-α, IL-1β).

• Hypercoagulable state → increased risk of venous thromboembolism (VTE).

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Clinical Features

1. Incubation Period

• Typically 2–14 days (median ~5 days).

2. Symptoms

• Mild illness (most common):

  • Fever, fatigue, dry cough, sore throat, headache.

  • Loss of taste (ageusia) or smell (anosmia).

  • Myalgia, diarrhea.

• Moderate to severe disease:

  • Dyspnea, chest tightness, hypoxia (SpO₂ <94%).

  • Pneumonia on imaging.

• Critical disease:

  • Acute respiratory distress syndrome (ARDS).

  • Sepsis and septic shock.

  • Multi-organ failure.

3. Risk Factors for Severe Disease

• Age >65 years.

• Chronic comorbidities: diabetes, hypertension, cardiovascular disease, COPD, CKD, obesity.

• Immunosuppression (cancer therapy, transplant, HIV).

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Complications

• Respiratory: ARDS, respiratory failure.

• Cardiovascular: myocarditis, arrhythmias, myocardial infarction.

• Thromboembolic: deep vein thrombosis (DVT), pulmonary embolism (PE).

• Neurological: stroke, encephalopathy, Guillain-Barré syndrome.

• Renal: acute kidney injury.

• Long COVID (Post-acute sequelae of SARS-CoV-2 infection): fatigue, brain fog, dyspnea, depression, persistent anosmia.

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Diagnosis

1. Laboratory Tests

• RT-PCR (gold standard): Detects viral RNA from nasopharyngeal or oropharyngeal swabs.

• Rapid antigen tests: Less sensitive, but useful for screening.

• Serology (IgM, IgG antibodies): Indicates past infection or vaccination.

2. Imaging

• Chest X-ray: Patchy infiltrates.

• CT chest: Bilateral ground-glass opacities, consolidation in severe cases.

3. Laboratory Findings in Severe Cases

• Lymphopenia.

• Elevated CRP, ferritin, IL-6.

• Elevated D-dimer (risk of thrombosis).

• Elevated troponin, liver enzymes.

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Management

Treatment depends on disease severity.

1. Supportive Care

• Rest, hydration, and antipyretics for mild cases.

• Paracetamol (acetaminophen): 500–1000 mg orally every 6 hours for fever/pain.

• Oxygen supplementation for moderate to severe cases (maintain SpO₂ ≥92%).

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2. Antiviral Therapy

• Remdesivir:

  • 200 mg IV on day 1, then 100 mg IV once daily for 5–10 days.

  • Recommended for hospitalized patients with moderate–severe disease requiring oxygen.

• Nirmatrelvir + Ritonavir (Paxlovid):

  • 300 mg nirmatrelvir + 100 mg ritonavir orally every 12 hours for 5 days.

  • For non-hospitalized high-risk patients within 5 days of symptom onset.

• Molnupiravir:

  • 800 mg orally every 12 hours for 5 days.

  • Alternative if other antivirals not available.

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3. Corticosteroids

• Indicated in patients requiring oxygen or ventilation.

• Dexamethasone: 6 mg orally/IV once daily for up to 10 days.

• Reduces mortality in severe/critical disease.

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4. Immunomodulators

• Tocilizumab (IL-6 inhibitor):

  • 8 mg/kg IV (max 800 mg), may repeat once after 12–24 hours.

  • Used in severe/critical disease with cytokine storm.

• Baricitinib (JAK inhibitor):

  • 4 mg orally once daily for up to 14 days.

  • Used as alternative immunomodulator in severe disease.

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5. Anticoagulation

• COVID-19 increases thromboembolic risk.

• Enoxaparin (LMWH): 40 mg SC once daily for prophylaxis.

• Therapeutic anticoagulation in confirmed VTE.

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6. Antibiotics

• Not routinely indicated unless bacterial co-infection suspected.

• If needed: amoxicillin-clavulanate or ceftriaxone based on local resistance.

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Prevention

1. Vaccination

• mRNA vaccines (Pfizer-BioNTech, Moderna).

• Viral vector vaccines (AstraZeneca, Johnson & Johnson).

• Inactivated vaccines (Sinovac, Sinopharm).

• Protein subunit vaccines (Novavax).

• Boosters recommended due to waning immunity and variant evolution.

2. Public Health Measures

• Hand hygiene, face masks, and physical distancing.

• Isolation of positive cases.

• Improved ventilation in indoor settings.

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Prognosis

• Most cases are mild and self-limiting.

• Severe cases may result in ARDS, organ failure, and death.

• Mortality rate varies (0.1–2%), highest among elderly and comorbid patients.

• Post-COVID syndrome (long COVID) affects up to 10–30% of survivors.

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Future Directions

• Ongoing development of next-generation vaccines targeting multiple variants.

• Research into long COVID mechanisms and treatments.

• Broad-spectrum antivirals against coronaviruses.

• AI-based predictive models for risk stratification and treatment planning.