Long COVID symptoms persist in as many as 1 in 8 adult patients, study finds

The authors say their study found about one in eight, or 12.7 per cent, of patients in the general population experienced long-term COVID-19 symptoms.

Judith Rosmalen, a professor of psychosomatic medicine at the University of Groningen and lead author of the study, said in a press release issued Thursday that including uninfected people in the research provides a more reliable estimate for how likely long COVID is in the general population.

The Canadian government, citing the World Health Organization, says between 10 and 20 per cent of people develop long COVID.

The main symptoms of long COVID examined for the Dutch study included chest pain, difficulty or painful breathing, muscle pain, loss of taste and smell, tingling in extremities, lump in throat, feeling hot and cold, heavy arms or legs, and general tiredness.

"There is urgent need for data informing the scale and scope of the long-term symptoms experienced by some patients after COVID-19 illness," Rosmalen said in the release.

"However, most previous research into long COVID has not looked at the frequency of these symptoms in people who haven't been diagnosed with COVID-19 or looked at individual patients' symptoms before the diagnosis of COVID-19."

The researchers began by asking participants of the Lifelines COVID-19 cohort study to regularly fill out digital questionnaires on 23 symptoms commonly associated with long COVID.

Lifelines is a multi-generational study involving more than 167,000 participants from the northern population of the Netherlands.

Questionnaires were sent 24 times to the same people between March 2020 and August 2021. The researchers say most of the data was collected before COVID-19 vaccines were rolled out in the Netherlands.

Participants were considered COVID positive if they had either a positive test or doctor's diagnosis.

The average age of the participants was 53.7 while 60.8 per cent were female.

Of the 76,422 participants, 4,231 had COVID-19. This group was then matched up with 8,462 uninfected people, taking into account sex, age and when a COVID-19 diagnosis was confirmed in a questionnaire in the positive group.

The study found 381 out of 1,782 COVID-positive participants (21.4 per cent) had persistent symptoms, compared to 361 out of 4,130 uninfected people (8.7 per cent).

Taken together, this means that in 12.7 per cent of patients, these symptoms can be attributed to COVID-19, the researchers say.

"Post-COVID-19 condition, otherwise known as long COVID, is an urgent problem with a mounting human toll," said PhD candidate and first author of the study Aranka Ballering.

"Understanding the core symptoms and the prevalence of post-COVID-19 in the general population represents a major step forward for our ability to design studies that can ultimately inform successful health-care responses to the long-term symptoms of COVID-19."

The authors say the study only involved patients infected with earlier COVID-19 variants — not including Delta and Omicron.

The true prevalence of COVID-19 also may be underestimated due to asymptomatic infections going undetected, the researchers said.

The study did not look at other long COVID symptoms that have since been identified as potentially relevant, such as brain fog, the researchers said.

As the study only looked at the northern Netherlands, the authors say the results may not be generalized to other areas.

Rosmalen says future research should also consider mental health symptoms, such as depression and anxiety, as well as those not included in the study, such as brain fog, insomnia and post-exertional malaise.