(Bloomberg) -- Younger adults in New York City are being hospitalized with Covid-19 infections at surprisingly high rates, said doctors and other health-care workers treating them, undermining earlier assumptions about who’s most at risk from the new coronavirus.

New York has more confirmed cases than anywhere else in the U.S., and 1 in 5 hospitalizations are occurring in people under age 44, according to data released by the city’s health department. Globally, moderate-to-severe cases have occurred in 10% to 15% of adults under age 50, according to the World Health Organization.

On Friday at Manhattan's Mount Sinai Morningside Hospital, a previously healthy 32-year-old male patient turned to doctor Kaedrea Jackson and asked: “Am I going to die?”

The young man, who had no underlying medical conditions, was short of breath with a fever, and his oxygen levels were dropping rapidly. He’d come to the hospital’s emergency department four days earlier but was told to go home, drink water, take Tylenol and self-isolate. Now he was back and his condition was deteriorating. “The level of fear in his eyes stood out to me,” Jackson, an emergency medicine physician, recalled in an interview Tuesday. “He was extremely scared. And he was so young.”

For months, the message from authorities had been that older people were at the highest risk. It was a belief so strongly held that health officials took to chastising people in their 20s and 30s to stay home—not to protect themselves, but to avoid transmitting the disease to older populations. That changed in mid-March, when a top White House health official warned that young people in Italy and France were falling ill. Now, the trend has shown up in the U.S.

“So many patients are not fitting the picture that we’ve been told from China or Italy. This is not just elderly patients; it’s anyone,” Jackson said. A confidential U.S. intelligence report has raised doubts about China’s reporting of the outbreak, including under-counting cases, Bloomberg News reported Wednesday.

As many as 20% of confirmed cases at the hospital have been under age 50, Jackson estimated. Many younger doctors in their 30s are watching healthy patients their age being admitted into the hospital and needing to be put on a ventilator.

“People are scared. These are patients where you’re thinking: ‘This just shouldn’t be happening to you. You’re so young. Why is this happening?”

A lack of widespread testing for the virus in the U.S. has made it difficult for health officials to know which groups are most at risk. But doctors and other health workers who spoke to Bloomberg described surprising numbers of younger patients who needed life-saving care.

“It’s young folks, previously healthy,” said Eric Wei, an emergency room doctor and chief quality officer at NYC Health + Hospitals, the city’s public hospital system. “They look like they have the flu. Within hours, they need oxygen. Within a few more hours they need a ventilator.”

At NYU Langone Health’s Medical Center overlooking the East River in Manhattan, dozens of patients in intensive care last week were under age 50, according to a worker who was providing direct medical care to them. A handful were in their 20s, and one was just 7 years old. The hospital declined to provide exact numbers of Covid-19 patients, details about their ages or whether they had underlying health conditions, citing patient privacy.

In China, which was hit first by the virus, just 4.3% of patients age 40 to 49 were hospitalized after developing Covid-19, according to a report published in the journal Lancet Infectious Diseases. It was even lower for younger people, with just 1% of those in their 20s and 3.4% of those age 30 to 39 requiring hospitalization, the report found.

Those gaps could be made up of differences in demographics, the share of people with pre-existing conditions or differing medical practices or resources. Italy, for example, has one of Europe’s oldest populations and people age 80 and up died at a rate of about 20%. In China, the fatality rate for the same age group was 15%.

“These cases in young and middle-aged people are striking,” said Paul Sax, clinical director of infectious diseases at Brigham and Women’s Hospital in Boston. “This isn’t how it was originally perceived from afar. There are definitely people who are surprised that this is a severe infection in this group, people who were previously totally healthy and exercising and doing just fine.”

In New York, 77% of the 914 patients who died had a medical condition such as diabetes, lung disease, heart disease or asthma, according to the city’s health department. Only 1.5% were otherwise healthy, with another 20% of the cases still under review. A broader analysis by the U.S. Centers for Disease Control and Prevention found a similar trend, that three-quarters of Americans who ended up in the ICU because of Covid-19 had one or more underlying health problems. Few people with such problems are able to recover without a hospital stay, the CDC said.

Risk Factors

Two-thirds of the U.S. is overweight or obese, factors shown to increase the risk of Covid-19. Nearly half of adults have high blood pressure. And 1 in 8 Americans haven’t visited a doctor in the past year, meaning that some may have health conditions and not know it.

Experts are seeing the same pattern emerging elsewhere in the U.S. as outbreaks grow. In Philadelphia, 56% of confirmed Covid-19 cases are under 40. A teenager lost their life in Los Angeles, a 12-year-old was intubated in Seattle, an infant was infected in Delaware and a 1-year-old baby died in Chicago.

For patients nursed through the infection with the help of a ventilator, there may be lasting health problems, said Ross McKinney Jr., chief scientific officer of the Association of American Medical Colleges. For even the youngest patients, doctors have to use ventilators set to high pressure, pumping in high levels of oxygen.

“Many will end up with damaged lungs and thereafter may be constrained in the future,’’ he said. “Any respiratory illness will make you sick, because you don’t have reserves, and things like running cross country or doing a 5K race may be out. You may not be able to be as active because your lungs don’t have the capacity anymore.”

The flood of young patients has been hard for doctors, said Jackson.

“It’s hard to lose anyone,” she said. But when physicians have to intubate patients in their 20s, 30s and 40s—that weighs heavy. “It’s the young, those with their full lives ahead of them who have no medical problems, they stand out. They are the ones that are hard to forget.”

©2020 Bloomberg L.P.