Coronavirus disease 2019 (COVID-19) is the infectious disease caused by the most recently discovered coronavirus.

The global pandemic of COVID-19 was first reported on 31 December 2019 by the World Health Organization country office following a cluster of pneumonia cases in Wuhan City, Hubei Province of China. 

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been confirmed as the causative virus of COVID-19.

In a phylogenetic analysis of 103 strains of SARS-CoV-2 from China, two different types of SARS-CoV-2 were identified, designated type L (accounting for 70 percent of the strains) and type S (accounting for 30 percent).

There appear to be two phenotypes in terms of the clinical presentation of severe cases - type L and H. 

Here is a useful article to read "COVID-19 pandemic—a focused review for clinicians"

References:

Gattinoni, L., Chiumello, D., Caironi, P. et al. COVID-19 pneumonia: different respiratory treatments for different phenotypes?. Intensive Care Med (2020). https://doi.org/10.1007/s00134-020-06033-2

Tang X, Wu C, Li X, et al. On the origin and continuing evolution of SARS-CoV-2. National Science Review 2020.

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