Monica Garcia smelled the acrid smoke before she saw the blue tarps. Soon, she spotted the cluster of makeshift tents next to a set of railroad tracks and peeked into one of them to find what she had learned to look for as an outreach worker to the homeless: a group of people living disconnected from the world. A small, deeply wrinkled woman who had rings on every finger and seemed especially fragile winced in the light, and Garcia drew closer. “Have you heard about what’s happening in our city and in the world right now?” she asked.

“You mean with the violence?” the woman said.

“No, something a little more severe,” Garcia said, and with that another conversation about the novel coronavirus was underway, this one with the most urgent of consequences.

With the coronavirus now embedded in every part of the United States and expanding rapidly, it has begun spreading among one of the most vulnerable populations of all, the more than half a million Americans who are homeless. Many of these people are sick, many are elderly, some are purposely staying in the shadows because of their immigration status, and a third have serious mental illness such as schizophrenia and paranoia that can make reasoning with them difficult. They are largely uninformed about the virus, and, because of their living conditions, are seen as crucial links in the spread of a pathogen that has the potential to overwhelm the country’s hospital capacity.

By the end of last week, homeless people in five states had tested positive for covid-19, and one, in California, had died. In Washington, D.C., Congress is working on emergency coronavirus packages to boost the health-care system and prop up the economy but has made no provisions for protecting or isolating the homeless, which means that task will fall to workers such as 41-year-old Garcia, who was now saying to the woman, “It comes from a person coughing. They say it’s going to hit harder among the most vulnerable — the sick, the elderly, and those who experience homelessness, and that’s you.”

Life on the front lines of the war against the coronavirus: a woman who has just found out about the pandemic starting to cry and saying she’s scared, and Garcia moving nearer to her to offer comfort. She was midway through a day that had begun just after sunrise when she left her two daughters, one a 4-year-old prone to respiratory infections, in the care of her severely asthmatic 72-year-old mother. Trained as a social worker, Garcia runs outreach for Haven for Hope, San Antonio’s central homeless shelter, one of the largest in the country. She is one of the few people still doing this work during the coronavirus crisis in a city whose homeless population is estimated at 3,000, and her shift had barely started when she got a call from a patrol officer and headed out into the strangely empty streets.

Garcia pulled into a Jack in the Box parking lot and saw six police officers standing around an agitated man in a stained blue hoodie. She walked past the officers and, unmasked and ungloved, crouched next to the man, so that her face was inches from his. “Hi, I’m Monica,” she said, hoping to calm him down. “Why do you have so many police around you?”

He looked at her for a moment, and when he extended his hand, she shook it. “I’m Stephen,” he said. He explained that the police were telling him to move along, and he was packing up his stuff. What Garcia wants most of all these days is to get people off the streets and into shelter, and she asked if he might consider coming with her. “We could get you some clothes, get you showered, and check on your Social Security benefits,” she said.

Stephen coughed, covering his mouth with his hand. He told Garcia he’d heard about the coronavirus that morning from the manager at Jack in the Box, which had closed its dining room, but he didn’t know much about it. “I’m out of the loop on all of this stuff,” he said and then mentioned that he was supposed to be on medication for mental-health trouble, that he used to be a famous artist, and that he might go to the shelter later that afternoon.

Garcia handed him one of her business cards and some clean clothing, and as she walked away, one of the patrol officers teased her good-naturedly for touching Stephen’s hand. “Keep your social distance,” Officer Robert Henderson said, faking a coughing fit and laughing. Garcia laughed, too, but explained that the work required her to get close. “I’m not going to not take his hand if he extends it out to me,” she said. “You can’t build rapport if you don’t shake hands. It’s like giving them a piece of dignity back.”

Before getting into her truck, she swabbed each of her fingers with a Clorox disinfectant wipe, squirted hand sanitizer in her palms, and sprayed Lysol over her sneakers. “Y’all have hand sanitizer?” she called to Henderson.

“We don’t have anything,” he said, so she passed him some wipes and sanitizer before driving off.

She wanted to get more hand sanitizer, but on her way back to the shelter she noticed a line of men sitting against a crumbling brick wall in the middle of an abandoned lot. At the end of the line was a woman, barely clothed, and Garcia pulled into the lot, walked past the men, and got as close to the woman as she could because she didn’t want the others to overhear their conversation. “Is everything okay?” she asked quietly. The woman didn’t answer directly. Instead, she said she needed to get a message to a case manager at Haven for Hope. Garcia assured her she would deliver it and turned to leave, and that might have been the end of it, except she noticed a heavy chain lying in the lot.

One thing Garcia has learned in her seven years of doing outreach is the possibility for violence. Fearing that the chain would be used as a weapon, she went back to her truck and for the first time that day put on a pair of gloves. She was walking back to the chain to pick it up when one of the men got to it first. He picked it up, walked toward her, and then past her toward her truck. The driver’s side door was open, and he reached in and dropped the chain on the floor.

“Good. So no one gets hit,” she said, thanking him.

Back at the shelter: On any given day, 1,000 people sleep in Haven for Hope’s dorm rooms and another 700 sleep on mats lined end to end on the floors of several old warehouses. The shelter is actually several buildings on the edge of downtown San Antonio. It’s the place where Garcia is trying to get people to stay, but now one of those people, Reinaldo Casola, was approaching Garcia saying he wanted to get out.

Garcia knew Casola, and when he extended his hand, she took it. A few weeks before, she had found him living in the shadows of a building, tucked under a wheelchair ramp. He had told her he had been mostly homeless since coming to the United States in the 1980s as part of a boatlift of Cuban refugees and was scared to go to a shelter because he was undocumented, but Garcia had coaxed him out and taken him to an immigration lawyer, who had assured him that it was safe.

Now, sitting on a bench with Garcia, nether of them masked, neither of them gloved, he told Garcia what had happened since he came to the shelter, that he had received a haircut, that he had qualified for food stamps, that he had been fitted for glasses. But he wanted to leave, or at least get out of the warehouse.

It was the thin mats, he said, so close together, and the hundreds of people snoring and coughing through the night.

“Look, you have to remember, you slept all alone for years,” Garcia said, squeezing Casola’s arm. “I can’t imagine how this must feel.”

“It makes me anxious,” he said.

“I told you, when you get your papers, you’ll be able to apply for housing,” she said.

“Right, right. I never tried to get my papers before because I was scared of la migración. I just don’t want you to forget about me. I’ll stay as long as you don’t abandon me,” he said.

“No, no, no, don’t worry. I won’t forget about you,” she said, and as they kept talking, she found herself paying attention to how close they were sitting, and how at some point in his life Casola had lost all of his teeth, and how people with no teeth sometimes can’t help spitting as they talk, and so she moved away from him, if only slightly.

She was starting to feel a little apprehensive, and a little overwhelmed. Back in her truck, back on the empty streets, she was on her way to check on an older woman she had recently discovered living in isolation under a bridge, but before she could get to her, her phone rang: A 19-year-old had somehow gotten her number and wanted a bus ticket to his father’s house in Missouri. As soon as she hung up, her phone rang again: A person who’d arrived at the shelter wanted to see her. It rang again: The police had received a trespassing complaint about a man by the railroad tracks. “I need to start setting priorities now,” she said, and decided to head to the railroad tracks first.

She parked by a stretch of warehouses along the railroad tracks and walked toward a man who turned toward her, revealing deep scratches on his face. He was alone but said he was in the midst of a conversation with his nephew. She waited until he was finished and shook his hand when he offered it, and then excused herself, went back to her truck, and as discreetly as possible, sanitized her hands. She understood he was too mentally ill to grasp the implications of the coronavirus, so she gave him some clean clothing and made a note to contact a city mental-health worker on his behalf, and then, smelling smoke, walked down the railroad tracks toward some blue tarps and the fragile-looking woman who was soon crying and saying she was scared.

“There’s a lot of us out here,” said the woman, whose name was Victoria.

Garcia moved closer, their shoulders now touching. “I don’t tell you this to instill any fear in you. I’m telling you so that you know enough about what’s happening that you can make decisions for yourself about how you’re living,” she said.

Victoria nodded, but kept crying.

Garcia pulled out her phone and leaned closer still to show Victoria a graphic that explained how to differentiate covid-19 symptoms from allergies or the flu. “So, basically, if you guys are going to decide to keep living out here, you need to watch out for anyone who is coughing, sneezing, has a fever, if they start feeling fatigue,” she said. “And if you decide that you want to try Haven out, I’ll give you my card and we’ll get you in.”

Victoria said that what she wanted in that moment was to wash her hands. So she followed Garcia back to the truck, along with a man and another woman from the encampment. “I don’t watch the news or nothing, so I’m just finding out,” the woman said, wiping her nose with her hand. “Have they found a cure yet?” the man wondered.

Garcia washed her hands and sprayed her sneakers and then handed Victoria and the others some Clorox wipes. She watched them swab their fingers and hands. She watched the wipes turn black. She watched them drop the wipes on the ground. She watched them walk back down the tracks.

She took a breath to calm herself. “It’s too many,” she said, and on it went through the afternoon.

There was a 73-year-old man living in an armchair in an abandoned carwash who needed help signing up for senior housing. “Your coming here is like providence,” he told Garcia. “I have one foot on the banana peel and coronavirus is going to find me.”

There was a young mother who promised Garcia she would give her parents her 3-month-old until the pandemic was over.

There was a man who said the coronavirus crisis was a hoax designed to bring down the U.S. government, and he coughed on Garcia without covering his mouth. There was the veteran of the Iraq War who said he was too high to be worried about the virus or anything else. There was another conversation with Henderson, the patrol officer she had given the hand sanitizer, when she returned to the shelter in the early evening and they stood in the courtyard area among dozens of people. “White House advises everyone to avoid groups of more than 10,” Henderson said, reading her a headline and laughing again.

And another conversation, this time with her boss, Haven for Hope President Kenny Wilson. Sitting six feet apart, they talked about Garcia’s growing worry that she herself could become a vector for the virus, and the uncertainty she had felt when she was talking to Victoria, the woman by the train tracks.

“At that moment, my feeling was, am I doing them more harm than good by sharing?” she said.

“Right. Yes. Because she can’t do anything,” Wilson said.

“I just wondered, should I have even told her that, and instilled that additional panic and fear in her?” Garcia said.

“But then, how can you not tell her?”

“Right, so it’s like you’re stuck,” Garcia said.

Wilson had already told Garcia that she might have to stop working with people on the street. Now, he raised that possibility again. “There could be a point where programming stops, and just food and shelter is what we’re doing,” he said. And he mentioned one more thing: The shelter might have its first covid-19 case. A resident had exhibited all the symptoms that afternoon, and staffers had moved him to a private room.

Her shift almost over now, the last thing Garcia had to do was drive the 19-year-old who had called her that afternoon to the bus station and buy him a ticket to Missouri. It was 7 p.m. and workers in protective gloves were selling tickets to a snaking line of travelers, some of whom were in masks. Garcia saw the anxiety in people’s faces and the way they moved, choreographing their steps to avoid bumping into anyone in the crowded station. All the conversations in English and Spanish were about the crisis. She led the young man, whose name was Cody, to a kiosk and touched the screen over and over to select the right ticket, staring at the smudge marks left by dozens of others and thinking about how she had seen on Facebook that the virus can live for days on surfaces.

“Really, thank you,” Cody said, watching her. “If it wasn’t for you, I’d be lost out of my mind, probably going to a mental hospital right now.”

Garcia knew how lonely Cody was and that he needed a hug, or at least an arm squeeze, but there was a fear overtaking her that she hadn’t felt before. Instead of soothing him, she handed him his ticket, gave the glossy paper a pat, and said, “That’s it, you’re off. Good luck to you,” and then went to the restroom to scrub her hands.

She headed home. She slept for a few hours. She was already awake at 5:30 a.m. when she got a call about a mentally ill woman walking the streets with a baby carrier. “Give me a kiss, my skinny bones,” Garcia said to her 4-year-old and went outside to her truck.

Later that morning, there would be a senior staff meeting at Haven for Hope to figure out ways to keep the shelter’s 255 employees safe and showing up for work. “People are starting to say ‘I’m scared to be here,’ ‘I’m uncomfortable being here,’ ‘I don’t want to take something home to my family,’ ” one the managers would say. His suggestion: “We can’t force people to come in, so I was thinking they can take a personal leave of up to 30 days, without pay. Because it’s their choice not to come in.”

Another manager would propose using guilt. “The message needs to be: We’re like a hospital. Like assisted living. You chose to work in a homeless shelter. You knew what it came along with. Especially as people start getting sick, we need you here 100 percent.”

Another would suggest appealing to an employee’s sense of pride. “When I hear messages of heroism and ‘we’re all in this together,’ it makes me want to pack up a suitcase and stay here for two months.”

Like so much of what was happening with the coronavirus, it was a problem without a clear solution, and meanwhile, Garcia was deep into her day, approaching a white-haired man in a wheelchair next to a Walmart parking lot. She saw that his sneakers were fraying and his fingernails black, and he seemed lost among the people wheeling carts filled with toilet paper and water bottles to their cars. But she did not move in close and crouch next to him. She stood six feet away. She was wearing bright orange medical gloves.

He looked up at her.

“Have you heard about the coronavirus?” she asked.