Illustration of a coronavirus particle. Coronaviruses are a group of viruses named for their appearance under electron microscopy, where their round-tipped surface spikes (blue) 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 pneumonia outbreak that started in Wuhan, China is caused by a new coronavirus, 2019-nCoV. The 2003 SARS outbreak was also caused by a novel coronavirus.