The U.S. Embassy and Consulates in Mexico are maintaining a web page of information about COVID-19 in Mexico. Last updated on March 2, it notes five documented cases in the country, a number likely to be higher today.
There is little or no new policy in Mexico regarding the virus, and while some spot checks for clear illness have been reported by people crossing into the U.S. from Mexico, no new exclusion policies on the part of CPB or ICE.
Perhaps most useful on the embassy page as it stands today is the phone number for the COVID-19 hotline now operated by the Mexican Ministry of Health. The Spanish-language hotline can be reached at 800 0044 800.