Coronavirus disease 2019 (COVID-19) is a respiratory tract infection caused by a newly emergent coronavirus – Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) – which was first reported in Wuhan, Hubei Province, China, in December 2019. Genetic sequencing of the virus suggests that SARS-CoV-2 is a betacoronavirus closely linked to SARS coronavirus.
The outbreak was declared a Public Health Emergency of International Concern on 30 January 2020, and has since spread globally, resulting in the 2019–21 coronavirus pandemic.
Current measures are in place globally to reduce the spread of the virus, most commonly from droplets (person-to-person) but also from infected surfaces. The target is to reduce the reproduction number (R0) to <1.0 – i.e. less than one person infected by one affected individual.
Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) is an enveloped, positive-stranded RNA virus.
The estimated reproduction number (R0) for SARS-CoV-2 ranges from 2.2 to 5.5, so one person can potentially transmit the disease to 5–6 people.
The majority of people with COVID-19 have uncomplicated or mild illness, but a relatively small proportion of people develop severe illness.
The immune response to SARS-CoV-2 involves both cell-mediated immunity and antibody production.
Diagnosis by PCR testing
Standard confirmation of acute SARS-CoV-2 infections is based on the detection of unique viral sequences by nucleic acid amplification tests.
Serological tests detect evidence of the body’s immune response to an infection, which can provide information on both current and prior infection, and on vaccine-induced immune responses.