The researchers found that several symptoms were new or more severe three to five months after having Covid-19, compared to symptoms before a Covid-19 diagnosis and to the control group, suggesting these symptoms can be viewed as the core symptoms of long Covid.
The core symptoms recorded were chest pain, difficulties breathing, pain when breathing, painful muscles, loss of taste and/or smell, tingling hands/feet, a lump in throat, alternately feeling hot and cold, heavy arms and/or legs and general tiredness.
The severity of these symptoms plateaued at three months after infection with no further decline. Other symptoms that did not significantly increase three to five months after a Covid-19 diagnosis included headache, itchy eyes, dizziness, back pain and nausea.
“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,” Aranka Ballering, doctoral student at University of Groningen in the Netherlands.
“Post-Covid-19 condition, otherwise known as long Covid, is an urgent problem with a mounting human toll. 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 healthcare responses to the long-term symptoms of Covid-19,” Ballering said.
The study included 76,422 participants, of which 4,231 (5.5 per cent) had Covid-19 and were matched to 8,462 controls.
The participants were regularly asked (24 times) to fill out digital questionnaires on 23 symptoms commonly associated with long Covid between March 2020 and August 2021.
Of the study participants who had submitted pre-Covid symptom data, the researchers found that 21.4 per cent (381/1,782) of Covid-19-positive participants, compared to 8.7 per cent (361/4,130) of the control group, experienced at least one increased core symptom at moderate severity three months or more after SARS-CoV-2 infection.
This implies that in 12.7 per cent of Covid-19 patients their new or severely increased symptoms three months post-Covid can be attributed to SARS-CoV-2 infection, the researchers said.