New York’s Metropolitan Transportation Authority announced Thursday that 23 workers have tested positive for the new coronavirus, as officials held a briefing for employees to allay fears about being infected on the job.

Until Thursday, the MTA said just one worker had tested positive for the virus. Some of the 23 infected workers had public-facing roles, the MTA’s chief safety officer, Patrick Warren, said in an interview. But in most cases they didn’t display symptoms while at work and were a low risk to riders, he said....