Metro officials said Thursday they want to maintain full subway and bus service as long as possible but are preparing for the possibility that they would need to scale back service if too many employees call in sick because of the novel coronavirus.

So far, about 3 percent of the agency’s employees remain absent daily, on par with normal rates, Metro officials said.

Concerns about the spread of the virus are having an impact on ridership, as Metro passengers took 100,000 fewer rail trips Wednesday compared with the same day last week, officials said. It was the first day that the rail system saw significant impacts, presumably due to employers encouraging workers to telework and commuters avoiding public transportation over fear of the virus. Bus ridership numbers aren’t yet available, officials said.

Metro General Manager Paul J. Wiedefeld said the agency wants to “maintain service as much as we can as long as we can” but is continuing to assess how to best keep customers and employees safe.

“We all know this is changing minute by minute, so we want to remain flexible,” Wiedefeld told Metro board members.

“We are going over what-ifs,” he said.

Wiedefeld added during a follow-up briefing with reporters: “A lot of people still need to get around — hospital workers, for instance. … I don’t envision shutting down the system, but again, let’s see how this plays out.”

Theresa Impastato, Metro’s chief safety officer, told board members the agency is identifying “critical functions” needed to operate and maintain the system.

“We’re accelerating the planning process for all potential scenarios,” Impastato said.

Wiedefeld said the agency is preparing for the chance that it might have to enter Phase 3 of the agency’s 15-year-old “Pandemic Flu Plan” for the first time. That would entail making service changes or cuts and opening the agency’s emergency operations center.

D.C. Mayor Muriel E. Bowser (D) said all events with more than 250 people in attendance must be postponed or canceled. (Mayor Muriel E. Bowser)

Metro has been in Phase 2 of the plan since Maryland Gov. Larry Hogan (R) announced late last week that the state had its first confirmed coronavirus cases. So far, Impastato said, the agency has been disinfecting railings, elevator buttons, seats and other “common touch points” in stations, rail cars, buses and Metro Access vehicles daily. It’s also monitoring employee absences and ridership after every morning and evening rush period.

Impastato told reporters the agency is in “consistent communication” with public health officials. If advised of an infected passenger in “near real time,” she said, the rail car, bus or MetroAccess vehicle would be taken out of service for a “full cleaning and sanitation,” and station entrances and other surfaces that the passenger might have touched would be sanitized.

Metro is planning ways to curtail service to do “spot cleaning” of stations, trains and vehicles as necessary, she said. Metro also could use SmartTrip card data to determine where an infected passenger traveled in the system, Impastato said.

Asked about the additional costs of virus-prevention measures, Wiedefeld said Metro is keeping track of its spending and could apply for federal aid in the future. However, he said, the agency is looking beyond those costs now.

“If we need more people out there or we need more supplies,” he said, “we’ll get them.”

Metro officials said they’re continuing to encourage rail and bus passengers to frequently wash or sanitize their hands as the best way to prevent the virus from spreading.