Coronavirus disease 2019 (COVID-19) is an infection caused by a newly emergent coronavirus – Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2). It shares a high degree of genetic homology with SARS coronavirus 1.
COVID-19 is recognised as having a 1-5 day incubation phase, during which an individual may have no physical symptoms of the disease, but may still be infectious and high titres of the virus can be detected on upper airway surfaces in some people who do not develop symptoms.
Most people will have only a mild illness with COVID-19, with non-specific symptoms such as fever, fatigue, cough (with or without sputum production), loss of taste and smell, anorexia (loss of appetite), muscle pain, malaise, sore throat, nasal congestion, dyspnea or headache. Patients may also present with diarrhoea, nausea and vomiting, but this is rare.
A relatively small proportion of those infected develop more severe disease, requiring oxygen therapy (14%) and approximately 5% will require intensive care unit treatment. Time from onset of infection to hospitalisation can be up to ~13 days. Of those critically ill, most will require mechanical ventilation. Most commonly severe pneumonia is diagnosed in severe cases, and this can progress to acute respiratory distress syndrome, life-threatening multi-organ dysfunction and death.
Patients with COVID-19 symptoms in intensive care have been shown to no longer carry the virus in the upper respiratory tract. Viral detection tests should assist in the decision on when to discontinue additional precautions for hospitalised patients.
Further information on serology testing
Testing for the presence of antibodies can tell us whether a person has been previously infected. Most patients who recover from coronavirus have been found to produce antibodies. However, it is not yet known if a positive result for antibodies, showing presence of IgG levels following being infected with SARS-CoV-2, will be protective, either fully or partially against future infection, or for how long protective immunity may last.
The host immune system reacts to infection with SARS-CoV-2 by producing antibodies. These antibodies are of 2 distinct different types, IgM and IgG. IgM antibodies appear more quickly after infection than IgG antibodies, but are also only transiently present. IgG antibodies to SARS-CoV-2 are produced in the later stages of infection with SARS-CoV-2, and are more persistent than IgM antibodies. This means IgG antibodies are detectable after viral RNA is no longer detectable.
Antibodies are a good indication of whether an individual has been exposed to SARS-CoV-2, but a lack of antibodies does not mean the individual has not been exposed.
Positivity for antibodies does not mean an individual is immune to subsequent reinfection by SARS-CoV-2, as it is still unclear if the antibodies being detected are neutralising/functional antibodies, nor does it give an indication of how long those antibodies may remain in the individual.
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References
- Department of Health (DoH), Coronavirus (COVID-19) Guidance: what you need to do. Available at: https://www.gov.uk/guidance/coronavirus-covid-19-information-for-the-public. Updated daily
- The Lancet, Covid-19 Resource Centre. Available at: https://www.thelancet.com/coronavirus-19/dgcid=kr_pop-up_tlcoronavirus20
- National Institute for Health and Care Excellence (NICE), NICE Guideline (NG) 159. COVID-19 rapid guideline: critical care. March 2020. Available at: https://www.nice.org.uk/covid-19
- Fauci, AS et al, Editorial – Covid-19 – Navigating the unchartered. NEJM 2020; 382:1268-1269<
- WHO: Coronavirus disease (COVID-19) Pandemic. https://www.who.int/emergencies/diseases/novel-coronavirus-2019
- WHO: Clinical management of severe acute respiratory infection (SARI) when COVID-19 disease is suspected. 13 March 2020 https://www.who.int/publications-detail/clinical-management-of-severe-acute-respiratory-infection-when-novel-coronavirus-(ncov)-infection-is-suspected
The COVID-19 tests may be performed by a 3rd party laboratory. Any 3rd party laboratory used is UKAS accredited and situated in the UK. UKAS accreditation specifically for the COVID-19 testing has been applied for as an extension of scope and is awaiting UKAS accreditation.
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