How is this not an infringement on the right to assemble?
For the Federal Goverment: https://en.wikipedia.org/wiki/Public_Health_Service_Act
The list (for the federal government) of diseases is managed via Executive Order [PDF] https://www.govinfo.gov/content/pkg/FR-2003-04-09/pdf/03-883...
The CDC also has a link to this: https://www.cdc.gov/quarantine/aboutlawsregulationsquarantin...
These measures have precedent, so good luck in getting these overturned.
https://www.supremecourt.gov/publicinfo/press/pressreleases/...
“The Court’s postponement of argument sessions in light of public health concerns is not unprecedented. The Court postponed scheduled arguments for October 1918 in response to the Spanish flu epidemic. The Court also shortened its argument calendars in August 1793 and August 1798 in response to yellow fever outbreaks.”