One in eight adults (12.7%) who were infected with Covid-19 experience long-term symptoms – often called 'Long Covid' – due to the virus, according to the results of a large Dutch study published in the medical journal The Lancet.
Some people continue to suffer from health problems such as chest pains, loss of smell and taste, difficulties breathing, fatigue or muscle pain, for months or even years after a Covid infection, but very little is known about what causes this.
"There is an urgent need for data informing the scale and scope of the long-term symptoms experienced by some patients after Covid-19 illness," Professor Judith Rosmalen from the University of Groningen, lead author of the study, said in a press release.
Researchers analysed the data of almost 13,000 Dutch people who have been completing questionnaires about their health regularly since March 2020. They compared the complaints of people who contracted Covid-19 with the complaints they had before they became infected, as well as with health complaints of participants who did not become infected.
'Core symptoms' of Long Covid
"This method allows us to take pre-existing symptoms and symptoms in non-infected people into account to offer an improved working definition for Long Covid and provide a reliable estimate at how likely it is to occur in the general population," said Rosmalen.
The results show that 12.7% of Covid-19 patients, 1 in 8, continue to experience long-term complaints, such as chest pain, difficulties or pain when breathing, painful muscles, loss of taste and/or smell, tingling hands and/or feet, a lump in the throat, alternately feeling hot and cold, heavy arms and/or legs and general tiredness.
The severity of these symptoms plateaued around three months after infection with no further decline. As researchers found that most of those symptoms were new (or became more severe) three to five months after the infection, these symptoms can be viewed as the "core symptoms" of Long Covid.
Other symptoms that did not significantly increase three to five months after a Covid-19 diagnosis included headaches, itchy eyes, dizziness, back pain and nausea.
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"Long Covid is an urgent problem with a mounting human toll. Understanding the core symptoms and the prevalence 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," Aranka Ballering, PhD candidate and first author of the study.
A recent study in Belgium, conducted by the Sciensano National Health Institute, published even higher Long Covid figures: 47% of patients still had complaints after three months, and 32% after six months.
The results of different studies vary widely, depending on what complaints are considered symptoms of Long Covid. What separates the Dutch study from the Belgian one is that participants in the Netherlands were already monitored before they were infected, as well as the comparison with people who were never infected.
This way, complaints from other causes unrelated to Covid-19 could be taken into account. The researchers now hope to further use the data to identify the exact causes of Long Covid and improve patient care.