COVID-19, SARS-CoV-2 - Transmission, Incubation, Symptoms, Complications, Risk factors

Last Modified: January 10, 2024

Introduction to COVID-19 (SARS-CoV-2)

COVID-19 (Coronavirus disease 2019) or SARS-CoV-2 ('Severe Acute Respiratory Syndrome coronavirus 2), is a contagious respiratory disease. Its causative agent is the virus SARS-CoV-2 and it was first identified in Wuhan, China, in December 2019.

The virus spread worldwide resulting in the COVID-19 pandemic. Worldwide, the pandemic claimed almost 7 million lives with less than half of the world's population getting the viral infection.

History of COVID-19 (SARS-CoV-2)

Since COVID-19 (SARS-CoV-2) was first discovered in Wuhan, China, it is also referred to as Coronavirus, Wuhan coronavirus, or Wuhan pneumonia. It is not uncommon to name diseases after geopolitical locations such as Zika virus, Spanish flu, or Middle East Respiratory Syndrome (MERS).

Based on the 2015 guidance and international guidelines against using geographical locations or groups of people to name any disease or virus, the World Health Organization (WHO) recommended the names 2019-nCoV and 2019-nCoV acute respiratory disease.

On 11 February 2020, WHO officially named the virus COVID 19 (coronavirus disease 2019) and SARS-CoV-2.

Transmission of COVID-19 (SARS-CoV-2)

COVID-19 (SARS-CoV-2) is transmitted when infectious SARS-CoV-2 particles are breathed in or the virus comes into contact with mucous membranes – eyes, mouth, and nose.

A person may be infected by touching their nose, mouth, or eyes with their hands after touching surfaces or objects contaminated with SARS-CoV-2.

The transmission rate of COVID-19 is highest while in close proximity. Small airborne particles containing the virus can also remain suspended in the air and travel over longer distances – especially in indoor environments.

Incubation period of COVID-19 (SARS-CoV-2)

Following exposure, the incubation period of COVID-19 (SARS-CoV-2) may range from one to fourteen days with the median at 4-5 days.

Among symptomatic patients, around 81% of the individuals develop mild to moderate symptoms which also include mild pneumonia. Meanwhile, 14% develop severe symptoms and 5% develop critical symptoms.

Any infected person (including asymptomatic) can act as a carrier i.e. remain contagious for up to 20 days.

Symptoms of COVID-19 (SARS-CoV-2)

The symptoms of COVID-19 (SARS-CoV-2) are widely variable and depend on the type of virus variant involved. The symptoms may also change over time. However, it has been reported that at least a third of the population do not develop noticeable symptoms but are still contagious.

The most common symptoms (81% of cases) of COVID-19 (SARS-CoV-2) include cough, fever, loss of smell (anosmia), loss of taste (ageusia), fatigue, and breathing difficulties. Anosmia and ageusia have been reported in 88% of symptomatic cases.

Less common symptoms are sore throat, runny nose, headaches, eye irritation, nasal congestion, muscle pain, and diarrhea.

Severe symptoms (14% of cases) include dyspnea and hypoxia with more than 50% lung involvement on imaging.

Critical symptoms (5% of cases) include respiratory failure, septic shock, or multiorgan dysfunction – which requires ICU admission.

Organ damage has also been observed in numerous cases.

In some patients, COVID-19 (SARS-CoV-2) symptoms may last for months or years at a time and are known as long COVID.

Overall three clusters of symptoms have been identified.

Respiratory symptom cluster – fever, cough, sputum, shortness of breath
Musculoskeletal symptom cluster – fatigue, headache, muscle pain, joint pain
Digestive symptom cluster – vomiting, abdominal pain, diarrhea

Complications of COVID-19 (SARS-CoV-2)

The common complications seen in patients with COVID-19 (SARS-CoV-2) are as follows:

Pneumonia
Acute respiratory distress syndrome (ARDS)
Multi-organ failure
Septic Shock
Elevated liver enzymes indicating liver injury (in 20-30% of cases)

Other complications depending on the site of infection or patients are:

Cardiovascular complications due to COVID-19 (SARS-CoV-2)

Heart failure
Arrhythmias
Heart inflammation
Thrombosis
Venous thromboembolism

Neurological complications due to COVID-19 (SARS-CoV-2)

Stroke
Seizure
Guillain–Barré syndrome (GBS)
Encephalopathy

Complications in children due to COVID-19 (SARS-CoV-2)

pediatric multisystem inflammatory syndrome – often fatal

Opportunistic infections after COVID-19 (SARS-CoV-2)

Fungal infections such as aspergillosis, candidiasis, cryptococcosis, and mucormycosis are seen in patients recovering from COVID-19 (SARS-CoV-2)

Risk factors of COVID-19 (SARS-CoV-2)

Old age: People of advanced age are at higher risk of developing severe symptoms.

Pregnant women: are more likely to develop respiratory and obstetric complications that can result in miscarriage, premature delivery, and intrauterine growth restriction.

Immunocompromised individuals: people undergoing immunosuppressive therapy or HIV/AIDS patients.