No one knows whether the coronavirus will substantially threaten the U.S., where it has already been detected, but one thing is certain: American hospitals aren’t ready for the deadly virus or a future global contagion. Travelers from China’s Wuhan region are being diverted to five U.S. airports, where they can be screened. That’s sensible, but it’s no substitute for improving hospital readiness.

If the virus becomes a domestic threat, American public safety will depend on what hospitals do when someone unknowingly infected...