What is COVID-19, and what do we know so far about its clinical presentation?
The virus responsible for COVID-19, SARS-CoV-2, is in the species SARS-like corona viruses. At 125 nm, it is slightly larger than influenza, SARS and MERS viruses. It is almost certainly a descendant from a bat corona virus of which there are many. The closest is a virus that originated from the Rhinolophus bat which is > 96% homologous with the current SARS-CoV-2 virus. It is only 79% homologous with the original SARS CoV [1].
The near identical gene sequences of 90 analysed cases from outside of China suggests it has likely emerged after a solitary species jump in early December 2019 from an unknown (likely mammalian) intermediate host [2]. Pangolins are an endangered ant-eating mammal from which scientists in Guangzhou have shown a coronavirus with 99% homology, with a receptor binding domain identical to that of SARS-CoV-2. However, this has not been confirmed, and, in addition, the pangolin's rarity means this may not be the only mammal involved.
The symptoms of COVID-19 are fever, dry cough, fatigue, nasal congestion, sore throat and diarrhoea. On February 14th, the Chinese Center for Disease Control and Prevention (China CDC) published the first details of 44,672 confirmed cases, in the biggest study since the outbreak began [3]. Their findings show that COVID-19 was mild for 81% of patients and had an overall case fatality rate of 2.3%. Of those confirmed cases, only 2.2% were under 20 years old. Compared to adults, children generally present with much milder clinical symptoms. It is likely that future serological studies will show much asymptomatic disease in children. As opposed to H1N1, pregnant women do not appear to be at higher risk of severe disease. The severity of the disease appears to be associated with age, with the elderly most at risk; those over 80 years of age had a Case Fatality Rate (CFR) of 14.8%. The CFR was also increased in those with comorbidities including cardiovascular, diabetes, chronic respiratory disease, hypertension, and cancer. The cause of death is respiratory failure, shock or multiple organ failure.