Coronavirus Disease 2019 (COVID-19) Signs and Symptoms

Definition

• A respiratory tract infection caused by a newly emergent coronavirus, SARS-CoV-2, that was first reported in December 2019

Etiology

• SARS-CoV-2 is classified within the genus Betacoronavirus (subgenus Sarbecovirus) of the family Coronaviridae
• An enveloped, positive-sense, single-stranded ribonucleic acid (RNA) virus with a 30-kb genome
• SARS-CoV-2 is most genetically similar to SARS-CoV-1 and both belong to the subgenus Sarbecovirus within the genus Betacoronavirus
  • However, SARS-CoV-1 is currently not known to circulate in the human population
• Infection is caused by binding of the viral surface spike protein to the human angiotensin-converting enzyme 2 (ACE2) receptor after activation of the spike protein by transmembrane protease serine 2 
• Variant of concern (VOC) is a SARS-CoV-2 variant with genetic changes that are predicted or known to affect virus characteristics such as transmissibility, virulence, antibody evasion, susceptibility to therapeutics and detectability
  • It is also identified to have a growth advantage over other circulating variants in more than one World Health Organization (WHO) region with increasing relative prevalence alongside increasing number of cases overtime, or other apparent epidemiological impacts to suggest an emerging risk to global public health
  • It would also need to meet one of the following criteria:
    • Detrimental change in clinical disease severity
    • Change in COVID-19 epidemiology causing substantial impact on the ability of health systems to provide care to patients with COVID-19 or other illnesses thus requiring major public health interventions
    • Significant decrease in the effectiveness of available vaccines in protecting against severe disease
  • As of 27 September 2024, there is no VOC
• Variant of interest (VOI) is a SARS-CoV-2 variant with genetic changes that are predicted or known to affect virus characteristics such as transmissibility, virulence, antibody evasion, susceptibility to therapeutics and detectability
  • It is also identified to have a growth advantage over other circulating variants in more than one WHO region with increasing relative prevalence alongside increasing number of cases over time, or other apparent epidemiological impacts to suggest an emerging risk to global public health

• As of 15 March 2023, WHO will assign Greek letters to VOC while VOI will be referred to using established scientific nomenclature systems (ie Nexstrain and Pango)
• Variants under monitoring (VUMs), based on WHO working definition by 4 October 2023, are variants of SARS-CoV-2 with genetic changes that are suspected to affect the characteristics of the virus and the early signals of growth advantage relative to other circulating variants (eg growth advantage which can occur globally or in only one WHO region), but with unclear evidence of phenotypic or epidemiological impact, requiring enhanced monitoring and reassessment pending new evidence
  • It is designated VUM if the variant has an unusually large number of mutations in known antigenic sites, but with very few sequences and not possible to estimate its relative growth advantage and if there is also evidence of community transmission in ≥2 countries within a 2- to 4-week period

Initial Signs and Symptoms

• Fever or chills
• Cough
• Dyspnea
• Chest imaging showing bilateral infiltrates
• Fatigue
• Muscle or body aches
• Headache
• New loss of smell or taste
• Sore throat
• Diarrhea

Epidemiology

• Globally as of 15 September 2024, there have been 776,281,230 total confirmed cases of COVID-19 according to WHO
  • There have been 7,065,880 confirmed deaths as of 15 September 2024
• Per region, confirmed cases based on WHO data as of 15 September 2024 are as follows: 
  • Americas: 193,299,394
  • Europe: 280,093,526
  • South-East Asia: 61,317,985
  • Eastern Mediterranean: 23,417,911
  • Africa: 9,582,835
  • Western Pacific: 208,568,815

Modes of Transmission

• Contact and droplet transmission through direct, indirect, or close contact with infected individuals through secretions (ie saliva and respiratory secretions)
• Airborne transmission occurs during medical procedures that generate aerosols (aerosol-generating procedures) 
• Fomite transmission is through contaminated surfaces and objects
  • Viable SARS-CoV-2 virus and/or RNA detected by RT-PCR can be found on those surfaces for periods ranging from hours to days, depending on the ambient environment (including temperature and humidity) and the type of surface
• Others like urine, feces, plasma or serum 

Factors that Determine Transmission Risk

• Whether the virus is still replication-competent
• Presence of symptoms (eg cough)
• Behavior and environmental factors associated with the infected person
• COVID-19 patient starts to gradually produce neutralizing antibodies that reduces the risk of virus transmission, usually 5-10 days after infection with SARS-CoV-2

Incubation Period

• Generally, after exposure to the virus, the mean time to develop symptoms is 4-6 days, with a range of between 1 and 14 days