Officials have said that the elderly and those with underlying conditions are most at risk to the virus.
According to the Daily Mail, Los Angeles doctor Samuel I. Fink started treating two male patients after they returned to the United States from a Northern Italy ski trip.
Fink is also friends with a third patient from the February trip who is also in ICU with the virus.
"I have never seen anything like this," Fink told the Daily Mail. "These people who are in the hospital are generally young — 40, 50, 60. These are not elderly people."
"It is my understanding that one has underlying medical issues, but the other two sure don't," he said. "Not having any underlying medical issues does not protect you."
He urged earlier this week that all schools close in order to cap the spread of the outbreak.
"I have practiced for over 30 years, and have seen it all, or so I thought. Nothing has worried me like this," he wrote in a Facebook post that was shared by thousands of users.
Some schools, universities and businesses have already taken that approach. About 23,000 students in the Northshore School District in Seattle are taking classes from home. Brands like Amazon, Apple and Microsoft are encouraging people to work remotely. And a number of outdoor music festivals like Coachella have been pushed back to later dates.