Covid-19, which is now a fast growing global pandemic. The number of confirmed cases in the US exceeded 1,000,000 due to rapid spreading of the virus.
Covid-19, spreads very easily, much easier than many other regular illnesses we deal with on a regular basis. That's what makes it so dangerous.
The best course of action is to stay at home to prevent the spread of the disease as well as hospital getting underwhelmed with patients who simply shouldn't be there.
As of today, there is no known cure and no approved vaccine for Covid-19.