Numerous people have reported lingering or new symptoms after a COVID-19 infection, though exactly how many people are struggling with long COVID has remained unclear.
Now, a new Dutch study finds about one of every eight (12.7%) patients who show long COVID symptoms.
The estimate is considered more reliable because researchers compared the number of people who experienced a new or increased health symptom three to five months after infection (21.4%) with those who experienced a new symptom but didn’t have an infection (8.7%).
The inclusion of uninfected populations gives a more accurate prediction of long COVID symptom prevalence and improved identification of the core symptoms of long COVID, according to the study. The findings were published Aug. 5 in The Lancet medical journal.
“There is urgent need for data informing the scale and scope of the long-term symptoms experienced by some patients after COVID-19 illness,” said study lead author Judith Rosmalen, from the University of Groningen in the Netherlands.
“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,” Rosmalen said in a journal news release.
The core symptoms the study identified were chest pain, difficulties breathing, pain when breathing, painful muscles, loss of taste and smell, tingling extremities, lump in throat, feeling hot and cold, heavy arms and/or legs, and general tiredness.
The study method “allows us to take preexisting symptoms and symptoms in noninfected people into account to offer an improved working definition for long COVID and provide a reliable estimate at how likely long COVID-19 is to occur in the general population,” Rosmalen said.
The researchers asked study participants to regularly fill out digital questionnaires on 23 symptoms commonly associated with long COVID.
The team sent the questionnaire 24 times to the same individuals between March 2020 and August 2021. Most of the data was collected before the COVID-19 vaccine rollout in the Netherlands, so the number of vaccinated participants was too small to analyze in this study.
Participants were considered to have been COVID-positive if they had a positive test result or a doctor diagnosis. This led to 4,231 (5.5%) of participants being recorded as having COVID. They were matched to 8,462 controls.
“These core symptoms have major implications for future research, as these symptoms can be used to distinguish between post COVID-19 condition and non-COVID-19-related symptoms,” study first author Aranka Ballering, a Ph.D. candidate, said in the release.
Ballering said that by looking at symptoms in an uninfected control group and in individuals both before and after infection, researchers were able to account for symptoms that could have resulted from stress caused by restrictions and uncertainty, rather than the virus.
Study limitations included that the research didn’t include Delta or Omicron infections. The prevalence of COVID-19 in this study may also be underestimated because of asymptomatic infection. Since this study was conducted, other symptoms, such as brain fog, have become potentially relevant. The study was also done only in one region and not with an ethnically diverse population.
“Future research should include mental health symptoms [e.g. depression and anxiety symptoms], along with additional post-infectious symptoms that we could not assess in this study [such as brain fog, insomnia and post-exertional malaise],” Rosmalen said. “We were unable to investigate what might cause any of the symptoms observed after COVID-19 in this study, but we hope future research will be able to give insights into the mechanisms involved.”