Follow our updates: The Centers for Disease Control and Prevention raised its travel warning to a level 3, its highest alert level, urging U.S. citizens to avoid all nonessential travel to China. The U.S. government is increasing staff to conduct screenings at 20 airports that handle almost all passengers traveling into the country from China.Mapping the spread of the new coronavirus: The United States, Germany, Sri Lanka, France, Thailand, Japan, Taiwan, Nepal, Hong Kong, Singapore, Vietnam, Macao and South Korea have all confirmed cases of the infection.Over the weekend, health officials confirmed three new U.S. cases, bringing the total to five. The patients — in Southern California, Chicago, Arizona and Washington state — had traveled from Wuhan.In Wuhan, the Chinese city of 11 million people where the coronavirus outbreak began last month, train stations, ferries, buses and the airport all have shut down. Travel bans were extended in central China to put more than 50 million people effectively on local lockdowns.What is coronavirus and how does it spread? Coronaviruses are a large family of viruses whose effects range from causing the common cold to triggering much more serious diseases, such as severe acute respiratory syndrome, or SARS. Do you have questions about the virus? Ask them here. And here’s what we know so far.