Conditions · Infectious and tropical diseases

COVID-19 !

COVID-19 is a respiratory infection by the SARS-CoV-2 coronavirus. Most cases are mild, but it can cause severe pneumonia, clots and lasting symptoms.

Updated 2026-11-01

Structures involved

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Microorganisms that cause it

SARS-CoV-2

Why it happens

What it is

An infectious disease caused by the coronavirus SARS-CoV-2, ranging from no symptoms or a mild cold-like illness to severe pneumonia, acute respiratory distress syndrome and multiorgan failure.

Who gets it

Caused a pandemic declared in 2020, with millions of deaths worldwide; Latin America, including Colombia, was among the most affected regions. It now circulates endemically with waves driven by new variants, and remains under surveillance within severe acute respiratory infection (IRAG) monitoring.

Causes

SARS-CoV-2, an enveloped RNA betacoronavirus
Spread mainly by respiratory droplets and aerosols, especially indoors with poor ventilation
Infectious from about two days before symptoms; variants differ in transmissibility and immune escape

Risk factors

Older age, the strongest risk factor for severe disease
Lack of vaccination
Obesity, diabetes, hypertension and chronic heart, lung, kidney or liver disease
Immunosuppression, cancer and advanced HIV
Pregnancy

Pathophysiology

The viral spike protein binds the ACE2 receptor, with help from the TMPRSS2 protease, on cells of the nasal and airway epithelium, type II pneumocytes and endothelium. Early disease is driven by viral replication; in severe cases a later inflammatory phase with cytokine release, endothelial injury and a prothrombotic state damages the alveoli, causing diffuse alveolar damage, hypoxaemia and thrombosis.

Classification

Asymptomatic or presymptomatic infection
Mild: symptoms without pneumonia or hypoxaemia
Moderate: pneumonia without severe hypoxaemia
Severe: oxygen saturation below 94% on room air, high respiratory rate or extensive lung infiltrates
Critical: respiratory failure, septic shock or multiorgan dysfunction

Symptoms and signs

Fever, chills and sore throat
Cough, fatigue, headache and muscle aches
Loss of smell or taste
Shortness of breath in moderate to severe disease
Silent hypoxaemia: low saturation with little sense of breathlessness

Diagnosis

Clinical: Respiratory symptoms, fever or anosmia, ideally with a history of exposure; severity is graded by respiratory rate, oxygen saturation and imaging.
Tests: RT-PCR on nasopharyngeal swab (reference) or rapid antigen test in the first days of symptoms. In hospital: lymphopenia, raised CRP, D-dimer, ferritin, LDH and troponin as markers of severity.
Imaging: Chest X-ray or CT: bilateral, peripheral and basal ground-glass opacities with or without consolidation; CT pulmonary angiography if embolism is suspected.

Differential diagnosis

Influenza and other respiratory viruses
Bacterial community-acquired pneumonia
Pulmonary embolism
Heart failure
Dengue in endemic areas

Goal of treatment

Most cases need only symptom relief and isolation. In high-risk and hospitalised patients the aims are to limit viral replication early, control the inflammatory phase, support oxygenation and prevent thrombosis.

Treatment

Conservative: Mild disease: rest, fluids and antipyretics, with home isolation and monitoring for warning signs.
Medical: Early antivirals (e.g. nirmatrelvir with ritonavir, remdesivir) for non-severe disease in people at high risk of progression, checking drug interactions.
Medical: Systemic corticosteroids for patients who need oxygen; in selected severe cases, immunomodulators such as IL-6 receptor blockers or JAK inhibitors.
Acute: Oxygen therapy, high-flow nasal oxygen, non-invasive or mechanical ventilation and prone positioning for respiratory failure.
Medical: Thromboprophylaxis with heparins in hospitalised patients.
Follow-up: Pulse oximetry, respiratory rate and level of consciousness; isolation with droplet and airborne precautions during aerosol-generating procedures.

Drugs for this condition

Complications

Acute respiratory distress syndrome and respiratory failure
Venous and arterial thromboembolism (pulmonary embolism, stroke)
Myocarditis and arrhythmias
Acute kidney injury and secondary infections
Multisystem inflammatory syndrome in children (MIS-C)
Post-COVID-19 condition (long COVID): fatigue, breathlessness, cognitive problems

Prognosis

Most people recover within one to two weeks. Mortality is concentrated in older and unvaccinated people with comorbidities. A minority develop persistent symptoms for months.

Prevention

Vaccination, prioritising older adults, people with comorbidities, pregnant women and health workers
Staying home and away from others when ill or after a positive test
Masks in health facilities and around vulnerable people, hand hygiene and ventilation of indoor spaces

Test yourself

Think of the answer, then tap the question to see it.

Which receptor does SARS-CoV-2 use to enter cells?

Angiotensin-converting enzyme 2 (ACE2), aided by the TMPRSS2 protease.

What is the typical chest CT pattern of COVID-19 pneumonia?

Bilateral, peripheral and basal ground-glass opacities, sometimes with consolidation.

Which COVID-19 patients benefit from systemic corticosteroids?

Those with severe or critical disease who need supplemental oxygen or ventilation; they are not used in mild disease.

Why do hospitalised COVID-19 patients receive thromboprophylaxis?

Because the infection causes endothelial injury and a prothrombotic state with a high risk of venous thromboembolism.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Coronavirus disease (COVID-19) (World Health Organization (WHO), 2025).

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