Last updated on:February 1st, 2023
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COVID-19 is an infectious disease caused by the coronavirus SARS-CoV-2. Coronaviruses are positive-sense single-strand RNA viruses with a crown-like envelope. Transmission occurs primarily via respiratory droplets. The mean incubation period is on average 5-6 days (with a 2-12 day range). The spectrum of illness can range from asymptomatic infection to severe pneumonia requiring ICU admission.
Asymptomatic patients have subclinical disease. This is defined as the absence of symptoms and signs of COVID-19.
Patients may complain of fatigue, myalgia, headache, weakness, and chills. These symptoms are thought to be due to the inflammatory response.
Fever is one of the most common symptoms of COVID-19. This is thought to be due to the release of pro-inflammatory cytokines that are triggered by the immune response to the virus.
These include cough (which is usually dry, but can be productive), dyspnea, rhinorrhea, sore throat and chest pain. These symptoms are thought to be due to the inflammatory response to viral infection of the bronchial epithelial cells and alveolar pneumocytes.
Nausea, vomiting, diarrhea and abdominal pain are common complaints. It is hypothesized that SARS-CoV-2 infects intestinal epithelial cells, impacting host microbial flora and causing gut inflammation.
This includes confusion or impairment of consciousness. New-onset anosmia and ageusia may also occur. This is thought to be due to the binding of SARS-CoV-2 to ACE2 receptors found in neurons, astrocytes, oligodendrocytes, and olfactory support cells.
Comorbidities such as advanced age (>65 years old), obesity, male gender, chronic comorbidities (severe cardiovascular disease, chronic obstructive pulmonary disease, chronic kidney disease, cerebrovascular disease, diabetes, liver disease) predispose to more severe symptoms and a greater mortality risk.
Symptoms of complications
Severe disease may result in interstitial pneumonia, acute respiratory distress syndrome (ARDS), impaired cardiac function, myocarditis, stroke, thromboembolic events, acute kidney injury, or multi organ failure. This is thought to be due to the cytokine storm that accompanies COVID-19 infection.