Illustration of coronavirus particles. Coronaviruses are a group of viruses named for their appearance under electron microscopy, where their round-tipped surface spikes make them resemble a crown. They can infect many animals and humans, causing respiratory diseases including the common cold, as well as more serious pneumonia. The 2019-2020 Covid-19 outbreak that started in Wuhan, China, is caused by the new coronavirus SARS-CoV-2 (previously 2019-nCoV). The 2003 SARS outbreak was also caused by a novel coronavirus.