“I don’t know what you’re feeling,” the supervising doctor said over the phone, his voice calm and reassuring. “But based on the text you sent me, you shouldn’t go to work.” The 29-year-old woman, an anesthesiology resident in her second year of training, breathed a sigh of relief. “Now,” the training-program director continued, “tell me what’s going on.” Two days earlier, on March 14, the young doctor finished her sixth straight day of 12-hour shifts in the surgical intensive care unit in her hospital in Boston. She was exhausted, but that wasn’t unusual. Yet when she woke up the next day, her only day off, she didn’t feel well. It wasn’t much — a queasy stomach, a little headache and brain fog. Her muscles were sore, as if she had lifted weights the day before. And when she took a deep breath, her chest felt strangely tight. She figured that she was just recovering from what had been a really tough week. The following day, she felt fine when her alarm went off at 5 a.m. She got to the hospital by 6, but before the day started, she was told she wasn’t needed. All elective surgery had been postponed because of the Covid-19 pandemic, and so there weren’t many patients in the surgical I.C.U. She and her co-resident made a deal: Her colleague would care for their patients that day, and she’d take over the next. Later that day, the subtle symptoms from the day before worsened. She didn’t feel sick exactly, just not like herself. She had been training for the Boston Marathon, before it was rescheduled for September, and she decided to go for a run. She finished her six-mile loop with no trouble, but she still felt a little off. Was she getting sick? Her husband, a doctor at the same hospital, didn’t feel sick, either, but for the past couple of days, he had a cough. Could this be Covid-19, the respiratory infection caused by the novel coronavirus SARS-CoV-2 — the virus that was sweeping across the United States and much of the rest of the world? Typical SymptomsFrom what she had read, that infection usually caused a fever, cough and shortness of breath. The young doctor had none of those. She had a bit of chest tightness, but it didn’t make her feel out of breath. She fretted about it all afternoon and deep into the evening. When she came across a story online about an emergency-room doctor who had symptoms like hers and tested positive for Covid-19, she made her decision and texted the director of her residency program. He called her right back. Latest Updates: Coronavirus Outbreak Despite pushback, Trump tells governors he “hasn’t heard about testing in weeks.” As governors beg, Trump promises ventilators to Europe. Despite scant evidence, the F.D.A. granted approval to use two malaria drugs. See more updates Updated 31m ago More live coverage: Markets New York “Stay home, and get tested,” he told her. The next day, she was tested. By then, her headache was a little worse. Her muscles ached a little more. She spent much of the day in bed. Her husband’s symptoms didn’t change; he still had the same dry cough. Neither of them had a fever. Two days later, she felt fine; not 100 percent but close. She went for her usual run. Guilt Sets InGiven how well she now felt, the young doctor wondered: Had she called in sick for a headache, unnecessarily increasing the workload on her fellow residents? There’s an informal motto that says a doctor should either “round or be rounded on.” You are well enough to work until you are sick enough to be in the hospital as a patient. A doctor should put patient care above everything else. A 2012 study found that more than half of all residents surveyed admitted to going to work when they were sick with flulike symptoms. And yet she knew that to go to work with even the slightest chance of a Covid-19 infection would be irresponsible. She hoped that the test would be positive — that she was right to call in sick even though she wasn’t very sick. It took four days for the results to come back. A nurse from her hospital called to let her know: She’d tested positive for Covid-19. Her husband, who hadn’t been tested, probably had the virus as well. Both of them would need to stay home for at least one week after the start of their symptoms, the nurse instructed. And before going back to work, both would have to have a negative test result. A Sense of VindicationAfter the phone call, the young woman was overwhelmed with relief. Later that morning, the head of her residency program called. How would she feel about letting her colleagues know about her diagnosis? This way they might feel better about calling in sick if they had symptoms that didn’t seem that bad. Remembering how important the story about the E.R. doctor had been in her own decision, she immediately agreed. She’d already called the people she interacted with on her last morning at work. In an email, she described her symptoms and the anxiety she had about calling in sick. “It can be tough to stay home, especially at a time like this, but it’s the best thing that we can do to keep our patients, families and each other safe,” she wrote. Once she hit send, she felt a sense of satisfaction, she told me. But that night, although she believed she was done with this virus, she found that it wasn’t done with her. Unexpected New SymptomsOn March 21, a week after her first symptoms, the young resident was reading a book when suddenly she felt as if her chest was squeezed tight, as if there was a band restricting the expansion of her ribs and lungs. She’d never felt anything like it before, and it scared her. She stood and felt lightheaded. “I don’t feel good,” she said to her husband. “I can’t breathe.” The suddenness with which this came on argued against its being a pneumonia. Could this be a panic attack? She tried taking deep breaths and relaxing. It didn’t help. She needed to go to the E.R., she told him. She put on a face mask, and the couple headed to the hospital where they worked. The woman fought against a rising sense of panic. Every stoplight seemed torture. There were reports of this virus causing sudden death. Was she dying? Would it just keep getting harder to breathe? In the emergency room, her heart was beating faster than normal, and she was breathing rapidly, but her oxygen level was fine. “Don’t leave me alone,” she pleaded with her husband and the nurse who took her to a negative-pressure room. Over the course of the next couple of hours, blood tests were done, and an EKG and X-ray were performed. Her doctors wanted to make sure she didn’t have something on top of her known viral infection. One blood test looked for an increase in white blood cells in her circulation — a sign of a possible bacterial infection. It was normal. The other tests were equally unrevealing. The EKG showed no evidence of heart damage. The chest X-ray showed no sign of a pneumonia. The weight on the young woman’s chest didn’t get better, but it got no worse. Early reports of Covid-19 cases in China showed that some patients who already had serious symptoms suddenly got worse a week or more into their illness, a so-called second-week crash. It’s still not clear exactly what might be causing this late exacerbation. After promising the doctors she’d come back if she felt any worse, the young doctor and her husband went home. Getting Back to WorkI spoke with the patient on March 26, and she told me she was feeling better. She gets a little out of breath when she climbs the four flights of stairs to her apartment, but even that is improving. Right now, she’s focused on going back to work — she recently tested negative. Although no one knows for certain if getting the infection provides long-term immunity, current thinking is that she is probably immune to the virus for now. She is eager to return to the fight and, given the proper equipment, is ready to take her place at the very front lines of this war.