Southwest Airlines shares slid after it said concerns about the coronavirus would hurt its revenue as passengers cancel or hold off on travel plans. The Dallas-based airline cut its revenue expectations for the first quarter by $200 million to $300 million. Southwest assumes the impact is tied to “concerns relating to reported cases of COVID-19,” the airline said. Airlines and other companies in the travel industry are suffering from fall out of the virus outbreak, which has many travelers opting to stay home. Southwest shares fell 4% Thursday. The shares are down 21% over the past 30 days.