When Jenny Managhebi comes home to her husband and two children these days, she wonders about the people she treated at UC Davis Medical Center — the ones who coughed and the ones who sneezed.

Ever since a patient with covid-19 was brought to the Sacramento hospital Feb. 19, Managhebi, who has been a cardiology nurse for 13 years, has grown concerned about catching the coronavirus, which causes the disease, and spreading it to other patients. She worries about whether she should still be volunteering in her 6-year-old’s classroom. She worries about whether she is adequately protected.

“Our job is to go and take care of people when they’re sick. I’m willing to take care of anyone. That's why we got into this line of work,” she said. But if too many health-care workers get sick, “we aren’t going to have a shot at fighting this thing.”

In widespread outbreaks of infectious disease, health-care workers are almost always hit hard. During the severe acute respiratory syndrome (SARS) outbreak in 2009, the Ebola crisis in West Africa from 2014 to 2016, and the early stages of the new coronavirus outbreak in China, caregivers were more likely than other groups to become infected. Many became severely ill or died.

The health-care system already has shortages of some critical personnel. As caregivers become infected or face isolation at home, maintaining the labor pool is one of the most important tasks that hospitals and nursing homes will confront in coming weeks, experts said, along with having the face masks, moon suits and other gear needed to protect them.

“Equipment is only as useful as the people you have to use it,” said Julie Fischer, who studies ways to protect front-line health-care workers for Georgetown University Medical Center. “Every system is about people.”

Already, the damage a single infection can do to a hospital staff has become alarmingly evident. The woman now being treated at UC Davis first showed up at a small community hospital in nearby Vacaville on Feb. 15, unknowingly exposing staff members to the coronavirus. After the virus was diagnosed, 93 health-care workers who had contact with her were placed in home isolation. About 34 began to show symptoms and were tested for the virus. Three tested positive.

NorthBay Healthcare, which operates the hospital, brought in workers from another of its facilities to fill in and paused nonessential services.

In Bronxville, N.Y., one man with coronavirus arrived at New York-Presbyterian Lawrence Hospital on Feb. 27 and came into contact with doctors, nurses and others. An unspecified number have been quarantined, according to the Westchester County executive.

And at UC Davis, where Managhebi works, some personnel have been sent home to monitor themselves for symptoms, although the nurses’ union and hospital administrators disagree on the number. The union said 124 people have been isolated; the hospital said that figure is inaccurate but declined to provide a total.

Some advocates for health-care workers say hospital administrators are not adequately protecting their staff members. This week, National Nurses United (NNU), the largest labor union for nurses, said that only 30 percent of the 6,000 nurses it has surveyed in 48 states think their workplace has sufficient protective gear to handle an influx of coronavirus patients. Only 29 percent said their hospital or clinic has plans for isolating patients if they are infected.

Michelle Mahon, assistant director of nursing practice for NNU, said nurses have reported delays in informing them if a patient has tested positive for the virus, outdated screening protocols and unclear guidance about patients donning masks at hospital entrances.

Some nurses reported that hospitals are keeping N95 respirator masks, which are the most effective at blocking respiratory droplets that spread the disease, and other specialized equipment off-site to prevent hoarding, preventing immediate access to one if a nurse needs it for a walk-in patient.

“What we’re seeing is a serious lack of coordination, ineffective central leadership and lack of clear direction. It’s created confusion and a disturbingly wide spectrum of preparedness, supply readiness and communication of plans,” Mahon said.

Those issues also affect the decentralized U.S. medical system, where most decisions are left to counties, states and facilities, under guidance and regulation by the federal government.

There are nearly 6,150 hospitals in the United States, 5,200 of which are considered community facilities, according to the American Hospital Association's website. That gives the United States about 925,000 staffed hospital beds, including 65,000 intensive care beds.

The health-care sector has 16.8 million workers, according to the Kaiser Family Foundation. But front-line caregivers are stretched thin across the system, with few in reserve for crises.

“The technical side is very clear,” Fischer said. “What is harder for hospitals to think about is how to manage health-care workers and supplies, given that we run so tight on both. There’s no slack.”

As the coronavirus spread across China, 3,387 health-care workers were infected by Feb. 24, almost all in Hubei province, the center of the outbreak, according to Chinese health authorities. Many were infected early in the epidemic, before China brought the spread of infection in hospitals under control, said H. Clifford Lane, clinical director of the National Institute of Allergy and Infectious Diseases, who visited China as part of the World Health Organization team that investigated the crisis there.

During the 2003 SARS outbreak in Toronto, a person with the virus came to the emergency department but was kept in a general observation area, where his infection spread to two other patients and a nurse who cared for all three, according to a study of the episode. The SARS virus soon spread to many health-care workers, including paramedics, a firefighter, five emergency room employees and a housekeeper. Cases appeared in other hospitals. Of the 438 people ultimately sickened by SARS in Canada, 375 were in Toronto, and most of the cases were acquired in hospitals. Of the 44 people who died, two were nurses and one was a doctor.

If U.S. hospitals eventually face a shortage of caregivers, they can call in retirees or press people like EMTs into clinical care, Fischer said. The U.S. Public Health Service Commissioned Corps has deployed more than 600 people to various places nationwide, including airport screening sites and U.S. Customs and Border Protection locations to assist with health screenings, a spokeswoman said. The agency, led by U.S. Surgeon General Jerome M. Adams, is looking to hire more personnel, she said.

Some medical centers are taking extra measures to protect current employees’ health and ensure that they will have sufficient staff to handle the outbreak.

“Preparedness is not about making us outbreak-proof. Nothing can do that,” said Fischer, the Georgetown University expert. “It’s about where we can introduce a little bit of slack into the system, a little bit of resilience in the system.”

Kaiser Permanente of Southern California has canceled nonessential travel and banned most large face-to-face meetings, according to an email to employees. At an urgent care clinic at the University of Pittsburgh Medical Center in Pittsburgh, where workers already were taking precautions amid a serious flu season, staff members are doing a little extra hand-washing and being more careful.

As they did during the SARS and Ebola outbreaks, “we just tightened our boots and made extra precautions just to try to identify that person who might have been at high risk,” said David Figucia, the clinic’s medical director.

The University of Nebraska Medical Center, one of the nation’s leading biocontainment and infectious disease facilities, has added special precautions for triaging patients with respiratory infections, such as having them wear masks upon entering and directing them to two designated clinics.

“But that only works when you’re talking about a handful of patients,” said Mark E. Rupp, medical director for infection control and epidemiology there. “A week from now, it may not be viable. Even us, we’re working on these things and scrambling to get them in place like many others are.”

It has become clear that some hospitals took the threat of pandemic seriously and have plans in place and that others “simply hoped this day would never come,” he said.

Melissa Nolan, an infectious-disease epidemiologist at the University of South Carolina, said it’s not clear whether otherwise healthy medical workers are at an increased risk of the most severe complications of coronavirus because of repeated exposure to the illness via their patients. One factor worth considering, she said, is the viral load a nurse or doctor may face.

Experts also agree that hospitals must assure workers that their families are cared for as they place their health in jeopardy caring for patients.

“I went into nursing to take care of sick people at the most vulnerable time in their life,” Managhebi said. “They might not always remember my name, but they remember how I made them feel during that time. That’s our job. And I’m willing to take care of anyone. But I’m not willing to risk my family’s safety.”

Hernandez reported from Vacaville, Calif. Joel Achenbach and Derek Hawkins contributed to this report.