With fears about coronavirus growing, San Mateo County is recommending the cancellation or postponement of “non-essential events.”

Top county health official Scott Morrow made the recommendation in a statement posted to the county’s website on Thursday afternoon as Santa Clara County public health officials called for new measures to prevent the virus’ spread, including cancelling large gatherings such as sports games and conventions, as well as for businesses to suspend non-essential travel.

“All non-essential gatherings should be canceled, postponed, or done remotely,” Morrow said. “Unfortunately, at this time, I have no standard definition of ‘non-essential’ or ‘gathering’ to guide your decisions. Use your best judgment.”

Morrow said the decision does not apply to schools, because they are essential. But he did recommend that school leaders determine what may be deemed a non-essential or extra-curricular activity at their respective campuses.

“COVID-19 is spreading in our community, the extent of which is unclear,” Morrow wrote. “It has likely been spreading for weeks, perhaps months. I have no reason to believe that how it’s spreading in other counties won’t be replicated to some degree here. We now all need to take assertive actions to inhibit the spread of this new virus.”

Schools in San Mateo County were open Friday.

The number of coronavirus cases in Santa Clara County reached 20 on Thursday.

Contra Costa County also revealed Friday morning that it is treating three more cases of coronavirus. Health officials there also are recommending that people with a higher risk from COVID-19, including adults over 50 and people with certain underlying medical conditions, should avoid mass gatherings, such as parades, sporting events or concerts.

Check back for updates.