At 4:50 a.m. one day in the middle of January, Valarie Smith was getting ready to clean yet another wide-body jet that had arrived at Los Angeles International Airport.

A year into her night-shift job, Smith knew the choreographed routine by heart. Picking up trash, wiping down seats, carrying out used blankets and pillows. This time, nerves got the better of her. Smith had heard of the emerging virus that was sickening people in China, so she asked her supervisor if the plane had come from Asia.

“I wanted to know if this jet had come in contact with coronavirus, and he just said he would never put anyone in jeopardy,” says Smith, 51. “I felt nervous. My boss and I had words.”

Daily developments on coronavirus:Get all the news and updates delivered to your inbox

Smith and her team cleaned the jet, armed with protective clothing, as well as gloves and masks. The unease stalks her daily.

“This is your health," she says. "Everybody’s nervous.”

As the COVID-19 virus spreads in the USA and around the world, officials at the U.S. Centers for Disease Control and Prevention encourage people to work from home as a way to help cut back contagion.

Daily coronavirus updates: Get them in your email. Sign up here

Not only do most U.S. workers not have that luxury – 29% have the option to work remotely, according to Labor Department data – many have frontline exposure to the virus because their jobs put them in front of people.

Airport workers, bus drivers, homeless shelter volunteers, teachers, medical professionals – the list of jobs that a work-from-home order would not apply to is vast. Interviews with representatives from some of those groups reveal a simmering level of concern for worker safety as COVID-19 cases and deaths increase.

That concern was heightened Wednesday after Department of Homeland Security officials announced that a medical screener working at the Los Angeles airport last month tested positive for the virus after attending to passengers, some of whom had arrived from China. The screener caught COVID-19 despite wearing protective gear, DHS officials said.

“If we see a full-on pandemic, there have to be national solutions put in place to protect workers and the general public to make sure people’s livelihoods aren’t destroyed,” says Steve Smith, spokesman for the California Labor Federation. “Officials are starting to say avoid crowds or being in close contact with people, but we have a lot of workers in that exact boat.”

Workers such as Maureen Dugan, a 31-year nursing veteran who works for the hospital associated with the University of California-San Francisco. Dugan says she is alarmed at the “lack of communication and training” for nurses as California grapples with COVID-19, which has stricken 58 people and sent 8,700 into self-quarantine.

“Our administrators say they’re planning, but nurses are left out of that planning,” says Dugan, who is on the board of the California Nurses Association. “If nurses aren’t safe, how are patients going to be safe? We just want to be properly trained, communicated to, supported and have protective equipment.”

That in part means N95 masks, which can help shield those near virus carriers but are in short supply globally partly because of a slowdown at Chinese factories. California Gov. Gavin Newsom announced Tuesday that the state received CDC approval to access in critical cases a stockpiled reserve of 21 million N95 masks.

University of California-San Francisco spokesperson Kristen Bole responded to questions about Dugan’s concerns with a statement that said, in part, that the hospital does not “as a matter of course notify staff when we receive patients with infectious diseases if they are not involved in the patient’s care.”

However, all staff caring for COVID-19 patients “are properly trained and are fully informed of their patients’ illness and condition,” the statement read.

How much does a coronavirus test cost? Fact check of COVID-19 medical bills finds that online rumor of a $3,000 charge is false

Coronavirus could be drivers' next fare

What if someone carrying the virus – perhaps without knowing it, since reports suggest that some COVID-19 carriers show no symptoms – steps into your workplace on a daily basis?

That’s the predicament for bus drivers such as Roger Marenco, whose election to lead San Francisco’s Transport Workers Union 250A temporarily put him behind a desk.

“This is the big talk of the town, if not the nation, but for us bus drivers especially so since we have one of the most dirty jobs,” says Marenco, who has driven buses and trolleys. “We’re exposed to anything and everything entering the bus, from people with mental issues to people who are truly ill.”

Marenco says drivers have come into the job healthy, and in a few years, “they have illnesses they’ve never had before.” He says he is at a loss as to how his colleagues can protect themselves from COVID-19, noting that one photo making the rounds on driver Facebook pages shows one driver wearing what looks like a gas mask in preparation for his route.

“Some officials now are saying a mask won’t even help,” Marenco says, echoing the surgeon general’s plea for citizens to stop buying masks as they don’t prevent infection and are needed by health care professionals.

“So they tell us to wash our hands a lot, but I worry there, too,” he says. “A lot of our guys have routes that get delayed and run late, so if they have a minute they just dig into their backpack and grab their lunch without washing. It’s scary.”

Coronavirus questions answered by a doctor:Should I panic? What are best prevention steps?

In some cities, officials deploy teams of hazmat-suited cleaners to wipe down public transportation to try to stem the spread of COVID-19, as well as reassure passengers. New York’s Metropolitan Transportation Authority cleans buses, subway cars and stations, reminding riders to wash their hands often and cover their coughs and sneezes.

“We want New Yorkers to know that we’re doing everything possible to keep our customers safe,” MTA CEO Patrick Doyle said Tuesday.

Biohazard experts familiar with viruses

Little surprise the phone has been ringing off the hook lately at the Brighton, Colorado, offices of Rocky Mountain BioHazard, which specializes in medical decontamination and crime scene cleanup.

Requests for tips and service quotes come in from airlines, customer-support call centers, libraries and homeless shelters, says company co-founder Donnie Lamirande.

“It’s the fear and uncertainty, but we try and keep things on an even keel,” she says. “When we freak out, you should freak out.”

The COVID-19 outbreak in the USA has not tripped Lamirande’s freak-out meter. Though the company’s services can often involve everything from a wipe-down of all surfaces to a chemical fog spray, she says in this case, frequent hand-washing and basic hygiene will go far in limiting the virus’ spread.

In Boston, the Pine Street Inn homeless shelter isn’t taking any chances. It brought in an outside contractor to regularly “deep clean” the facilities, in addition to installing hand-washing stations with soap, water and sanitizer.

Workers remind clients to visit an onsite health clinic if they show any symptoms, says Lyndia Downie, president of the 670-bed shelter.

“As with any health threat, we are concerned about our staff, guests and tenants and will be closely following this outbreak and putting as many precautions in place as possible,” she says.

The Denver Rescue Mission, which has nine locations across Colorado, hands out gloves and masks to anyone coming in coughing or sneezing. Denver Rescue Mission CEO Brad Meuli says staffers who don't feel well are encouraged to stay home.

For workers at the shelter – like many people whose jobs involve serving the public – their armor against COVID-19 amounts to a combination of good protective habits and a fatalism born of dedication.

“It’s not like our folks aren’t used to facing the possibility of getting sick every day,” Meuli says. “These folks are really committed people. You have to be.”

Airplane cleaner Smith considers herself a committed employee. She was upset when her supervisor at JetStream Ground Services questioned her dedication after she expressed concern about boarding a plane whose originating city was a mystery.

"I try not to worry about it or get upset about it, but I feel like management looks at those of us who show concern differently," Smith says. Emails, as well as a message left with Jupiter, Florida-based JetStream Ground Services, were not returned.

After the rapid spread of COVID-19 since Smith nervously boarded that plane a couple of months ago, many airlines have cut back or canceled flights from China and other heavily affected countries. That doesn't totally allay her concerns.

"I have to go home to my husband and kids, who are worried about me but also about themselves naturally," she says. “I like my job, it pays the bills. But I don’t want my life at risk."

Follow USA TODAY national correspondents @marcodellacava and @TrevorHughes