One in three people infected with coronavirus will experience at least one symptom of long COVID, a new study suggests.

Much of the existing research into the condition, a mixture of symptoms reported by people often months after they were originally ill with COVID-19, has been based either on self-reported symptoms or small studies.

Now researchers at the University of Oxford, the National Institute for Health Research (NIHR) and the Oxford Health Biomedical Research Centre (BRC) have shed fresh light on the scale of the problem after studying more than 270,000 people recovering from coronavirus in the US.

They found 37% of patients had at least one long COVID symptom diagnosed three to six months after infection. The most common symptoms were breathing problems, abdominal symptoms, fatigue, pain and anxiety or depression.

“The results confirm that a significant proportion of people, of all ages, can be affected by a range of symptoms and difficulties in the six months after COVID-19 infection,” said NIHR academic clinical fellow Dr. Max Taquet. “Over one-third of patients were diagnosed with at least one of the long COVID symptoms between three and six months after their COVID-19 illness.”

Severity of infection, age, and sex affected the likelihood of long COVID symptoms, according to the data from the US-based TriNetX electronic health record network.

Long COVID symptoms were more frequent in those who had been hospitalized, and they were slightly more common in women, the study published in the journal PLOS Medicine showed.

Different factors also influenced which of the symptoms people were most likely to experience. For example, older people and men had more breathing difficulties and cognitive problems, whereas young people and women had more headaches, abdominal symptoms and anxiety or depression.

COVID patients admitted to hospital were more likely to suffer cognitive problems like brain fog and fatigue compared with people who did not need to be admitted, the research found. People who did not need hospital care were more likely to have headaches than those who needed to be admitted. Many patients had more than one long COVID symptom, the researchers found.

“These data complement findings from self-report surveys, and show that clinicians are diagnosing patients with these symptoms. We need appropriately configured services to deal with the current and future clinical need,” said Taquet.

The study also looked at the same symptoms in people recovering from flu. People who get flu can have prolonged symptoms similar to those seen in some patients with long COVID, the study suggests, but lasting symptoms occur to a far lesser extent in those who had influenza.

Symptoms linked to long COVID were 50% more common among those who had COVID compared with those who had flu, the researchers estimated.

Amitava Banerjee, Professor of Clinical Data Science and Honorary Consultant Cardiologist, University College London, who was not involved in the research, said it was a “large, well-conducted and thorough study.”

He said the findings supported the calls that have been made for “large-scale rollout of health services” for those with long COVID, including those not hospitalized with COVID.

“Over half of patients (57%) had at least one long COVID feature recorded in the six months after infection and one-third (37%) in the 90 to 180 days after diagnosis,” said Banerjee.

The study had limitations, such as the fact it had focused on the nine symptoms probably most common among those with long COVID, he stressed. However, because as many as 200 signs of long COVID have previously been suggested, “the reported incidence” of long COVID was actually “likely to be an underestimate.”

He added that the fact the nine symptoms were all more common after COVID-19 than for flu was “yet another arrow in the quiver against bogus ‘this is just like flu’ claims.”

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