NEW YORK — One day in March 2020, Ms Rosemary Bily suddenly grew so tired she could barely get out of bed. “She slept a lot,” said her son-in-law Rich Lamanno.

“She was wiped out for most of a month.”

Ms Bily, now 86, also developed nausea and diarrhoea, along with a slight cough, and subsisted mostly on Tylenol and Gatorade.

A few days later her husband, Mr Eugene Bily, 90, started coughing and became lethargic as well.

Had it not been for a family gathering a few days earlier, the Bilys’ children would not have suspected the new coronavirus. They might have blamed the flu, or simply advancing age.

“What we heard on TV was ‘high fever, can’t breathe’ — and they had neither,” Mr Lamanno recalled.

But about a dozen guests had gathered at a restaurant in Rockville Centre, Long Island, earlier that month to celebrate a niece’s birthday, and one by one most of them fell ill with Covid-19, including Mr Lamanno and his wife.

As the symptoms spread, doctors told the worried family that the Bilys most likely had Covid-19. Because tests were in short supply at the time, neither was tested; the family also feared taking them to overflowing local hospitals. But subsequent antibody tests confirmed that the elder couple, who live in Oceanside, New York, had contracted and survived the virus.

The population older than 65, most vulnerable to the virus’ effects, got an early start on Covid-19 vaccination and has the highest rate in the country — more than 80 per cent are fully vaccinated. But with infections increasing once more, and hospitalisation rising among older adults, a large-scale new study in the Journals of Gerontology provides a timely warning: Covid-19 can look different in older patients.

“People expect fever, cough, shortness of breath,” said Dr Allison Marziliano, lead author of the study. She is a social and health psychologist at the Feinstein Institutes for Medical Research, part of the large Northwell Health system across New York state.

But when the researchers combed through the electronic health records of nearly 5,000 people, all older than 65, who were hospitalised for Covid-19 at a dozen Northwell hospitals in March and April 2020, they found that one-third had arrived with other symptoms, unexpected ones.

The team, searching through records using language software, found that about one-quarter of older patients reported a functional decline.

“This was falls, fatigue, weakness, difficulty walking or getting out of bed,” Dr Marziliano said.

Eleven per cent experienced altered mental status — “confusion, agitation, forgetfulness, lethargy,” she said. About half the group with atypical symptoms also suffered from at least one of the classic Covid-19 problems — fever, trouble breathing, coughing.

“Clinicians should know, older adults should know, their caregivers should know: If you see certain atypical symptoms, it could be Covid-19,” Dr Marziliano said.

The rate of atypical symptoms rose significantly with age, affecting about 31 per cent of those 65 to 74, but more than 44 per cent of those older than 85. These symptoms occurred more commonly in women, in Black patients (but not in Hispanics) and in those who had other chronic diseases, particularly diabetes or dementia.

Because people in the atypical group were less likely to experience breathing problems and require ventilation, they were less likely to need intensive care. But both groups spent about 10 days in the hospital, and roughly one-third of each group died.

“These people were in the hospital for as long,” Dr Marziliano said. “Their mortality rate was as high. So this shouldn’t be dismissed.”

The research mirrors findings from other, smaller studies of older people conducted early in the pandemic in the United States and Europe. During a Covid-19 outbreak in a nursing home in Providence, Rhode Island, for instance, a Brown University study found that the most common symptom was loss of appetite, followed by lethargy, diarrhea and fatigue.

“We’re not necessarily surprised by this,” said Dr Maria Carney, a geriatrician and an author of the Northwell study. “Older adults don’t always present like other adults. They may not mount a fever. Their metabolisms are different.”

Younger diabetics, for instance, may become sweaty and experience palpitations if their blood sugar falls, Dr Carney explained. An older person with low blood sugar could faint without warning. Older people who suffer from depression may have appetite loss or insomnia but not necessarily feel sad.

In May 2020, Dr Carney heard from a daughter worried about her mother, who was in her 80s and had suddenly grown weaker.

“She didn’t have fever or a cough, but she was just not herself,” Dr Carney recalled. Doctors at a local emergency room had diagnosed a urinary tract infection and prescribed antibiotics, the daughter reported. But five days later, her mother’s condition was worsening. “She needs a Covid-19 test,” Dr Carney advised.

Diagnosing Covid-19 quickly in older patients can make a world of difference.

“We have things to offer now that we didn’t have in the first wave,” said Dr Eleftherios Mylonakis, chief of infectious diseases at Warren Alpert Medical School of Brown University, who led the Providence nursing home study. “We have better understanding, more treatments, better support.”

Among the improvements: Using anticoagulant drugs to prevent clotting and using monoclonal antibodies (the treatment that former president Donald Trump received at Walter Reed Hospital in Bethesda, Maryland) that strengthen the immune system.

But, Dr Mylonakis added, “It’s paramount to start any kind of treatment early.”

With widespread vaccination, the symptoms of Covid-19 in older adults may become even more subtle. Fevers are easy to measure, and difficulty breathing will send anyone to an emergency room, Dr Carney pointed out, whereas “we don’t necessarily notice if someone has stopped eating”.

Her counsel, for older patients and their caregivers and doctors, is to stay alert for changes that occur quickly, over a matter of days. “When there’s a change in behaviour, physical or cognitive, it may not look like an infection, but keep Covid-19 at the top of your list,” she said.

The woman with the worried daughter had indeed contracted the virus; she died in a hospital.

But the Bilys pulled through and still live in their Oceanside split-level home. Mr Eugene Bily contended with many health problems even before the pandemic. In the past 18 months, he underwent two hip surgeries and several other hospitalisations. In June, he began receiving home hospice care.

Ms Rosemary Bily, however, has fully recovered from the virus. At 86, she drives to the supermarket and the drugstore, visits her hair salon weekly, keeps in touch with family via iPad and smartphone and helps care for her granddaughters.

“She’s doing well,” Mr Lamanno said. “She has resumed her normal life.”

This article originally appeared in The New York Times.