By Melanie Evans 

After finishing her shift, Katherina Faustino waits for other intensive-care nurses at the Nevada hospital where they work. They don’t leave immediately. “We go to the chapel,” she said. “We pray.”

Ms. Faustino has been shaken by the sheer number of Covid-19 deaths she has witnessed in recent months as Dignity Health-St. Rose Dominican, Siena Campus faced a flood of patients that filled its ICU beds for weeks.

“If you weren’t religious, you probably are now,” she said.

The longest and most deadly surge of the pandemic may be approaching a plateau nationally, but the rising, monthslong flood of new cases and hospitalizations is still cresting in some parts of the U.S. Throughout, the crisis has taxed nurses and doctors to a degree many said they have never experienced. High death tolls and the physical and emotional demands at work have left them exhausted and sometimes feeling hopeless, they said.

The surge has swept the country since late September. In interviews over recent months, doctors and nurses in several hard-hit states—including California and Nevada, where hospitalizations remain high—said their work and lives were altered in ways big and small by the flood of critically ill patients and the many who didn’t survive. “The despair is unbelievable,” Silvia Perez-Protto, a physician and medical director of the Ohio-based Cleveland Clinic Center for End of Life Care, said in December, the month Covid-19 hospitalizations peaked in that state.

Such stress can also pose risks to public health, according to researchers who surveyed nurses and patients across more than 250 New York and Illinois hospitals in the months before the pandemic. The study, published in August in the British Medical Journal Quality & Safety, found that nurses with higher workloads were more likely to report poorer safety conditions, burnout and plans to leave their jobs within a year.

“We have taken steps to streamline processes while continuing to deliver safe, quality care, but we can only do so much,” said Gordon Absher, a spokesman for three southern Nevada hospitals owned by nonprofit CommonSpirit Health, including St. Rose. Typically, nurses care for fewer patients but the surge has taxed those ratios. “The challenges of the pandemic are real and continuing,” he said.

National figures show some decline in new Covid-19 cases, but it is too early to say whether the shift will continue, said Johns Hopkins University epidemiologist Jennifer Nuzzo. “There might be a glimmer of hope in the data,” she said, but she cautioned that testing may have plateaued nationally, which could leave infections undetected.

The surge has overwhelmed some facilities and forced doctors to make uncomfortable choices about which patients get into crowded hospitals and intensive-care units, doctors said. Some hospitals in California alerted the state they reached a crisis point in recent weeks.

The latest surge began in late September. It has been longer and more deadly than spring and summer surges.

A widely used measure to track infection trends—the two-week average of daily new cases—rose for about six weeks during the pandemic’s first two U.S. surges. The measure has now largely climbed for four months, with lulls during data lags around the Christmas and New Year holidays. It has begun to decline in recent days.

Covid-19 hospitalizations and deaths surged with rising cases. “We’ve seen so many deaths,” Ms. Faustino said. She has seen families devastated by multiple losses. She and her family also had Covid-19, she said.

Ms. Faustino’s Henderson, Nev., hospital is in Clark County, which also includes Las Vegas. Between 94% and 96% of the county’s intensive-care beds have been occupied, on average, every week since Dec. 4 through Jan. 14, according to an analysis of federal data by the University of Minnesota Hospitalization Tracking Project.

The hospital recently created new units for critically ill patients. Still, some patients in need of care sit in limbo in the emergency room, waiting for an open bed. Intensive-care nurses typically care for one or two patients maximum; Ms. Faustino now cares for three to four. “I can’t believe I do this every day,” she said.

“Like many hospitals during the pandemic, our facilities have faced challenges in both patient capacity and staffing,” Mr. Absher said. “Our team has performed incredibly under the pressures presented by the pandemic,” he said.

The hospital recently created more space for critically ill patients by halting nonessential procedures, Mr. Absher said.

Covid-19 hospitalizations in Southern California also remain high. Weekly average hospital intensive-care occupancy continued to climb across Los Angeles County through Jan. 14, the University of Minnesota analysis shows. Roughly 59% of hospital ICU beds were filled by Covid-19 patients. Severe strain on hospitals across Southern California has delayed ambulances and stalled critical patient transfers.

In some California hospitals, emergency-room patients wait in tents and hallways. Doctors more closely scrutinize who gets an increasingly rare open bed. Nurses care for more patients. California has granted more than 160 hospitals temporary waivers from state nurse-to-patient ratios.

That includes Henry Mayo Newhall Hospital in Valencia, Calif., in Los Angeles County. The hospital reported sharp financial losses from the pandemic between March and June in publicly available disclosures to lenders. It also announced in June that it would lay off 35 nurses and dozens of other employees, making the required disclosure to the state and a nurses’ union.

“We’re deep in the trenches and it seems like it’s not ending,” said Nerissa Black, a nurse at Henry Mayo Newhall who is also the California Nurses Association’s chief nurse representative at the hospital. “I’m treading water just to get through.”

Ms. Black, who works in a unit for patients who need their hearts closely monitored, said she now cares for six patients each shift, up from four. All patients on her unit have Covid-19. Her new patient load leaves 10 minutes per patient per hour, a rushed pace that has left her worried she could make a mistake, she said.

In that tight schedule she must find time to carefully put on and remove protective gear; clean equipment; relay information from laboratories and physicians; and speak with social workers, chaplains and families.

Ms. Black apologizes often, she said, because she must get to critical medical tasks before she can answer less urgent requests from patients. “I feel guilty,” she said. “This is not like anything I’ve seen or experienced before.”

Henry Mayo Newhall spokesman Patrick Moody said: “We are profoundly grateful and proud of our employees and physicians for the incredible dedication and courage they have shown this past year.”

Elsewhere in Los Angeles, physician Marguerite Thorp is now confronted with patients she cannot help as she normally would. Because hospitals are so crowded, doctors’ first choice for treatment is often delayed or not available, she said. “Just knowing what they need doesn’t mean you can get it to them.” She still feels responsible. “It’s hard not to take that personally,” Dr. Thorp said.

She has also seen the virus grow increasingly pervasive in recent weeks. Longstanding challenges with affordable housing have exposed area households to risk as workers bring the virus home to a full household, she said.

“It sometimes feels really hopeless,” Dr. Thorp said. “I’m still figuring out how we’re going to get through this.”