What Exactly Is Long COVID? Different Definitions Make Diagnosis and Treatment Difficult
It’s difficult to predict the prevalence of a condition when you don’t know what it is, and it’s even more difficult to diagnose and treat it. But that’s essentially what’s happening with long COVID, a chronic condition that can emerge after an initial infection of SARS-CoV-2.
According to a new analysis in JAMA Network Open, the different definitions of long COVID that appear in published research are so dissimilar that they can result in dramatically different estimates of long COVID prevalence, making the condition much more difficult to research, diagnose, and treat.
“The findings highlight the need for a standard definition for long COVID,” said study author Lauren Wisk, an assistant professor of medicine at the University of California, Los Angeles, according to a press release. “Up to one-third of the variation in the published studies may stem from the fact that they use different definitions for long COVID.”
Read More: What is Long COVID and What Are the Symptoms?
Different Definitions of Long COVID
Since the start of the COVID-19 pandemic, millions of patients have reported that their symptoms have seemed to stick with them, continuing well after their initial infection. This chronic condition is commonly referred to as “long COVID,” and it is often associated (though not always) with symptoms such as fatigue, fever, and aches and pains, as well as complications with memory and concentration.
But despite the abundance of published studies about this chronic condition, there are discrepancies between the different definitions that different studies use, leaving researchers and clinicians without a clear understanding of long COVID and its pervasiveness.
Setting out to assess the prevalence of long COVID in a pool of around 4,700 U.S. patients, Wisk and her colleagues selected five definitions of long COVID from previously published studies from five countries, including the U.S., the U.K., and the Netherlands, as well as Sweden and Puerto Rico. They then applied those definitions to the data from their participant pool to assess the prevalence of long COVID among the patients.
Differing by the nature and the duration of symptoms, the five distinct definitions resulted in five distinct estimates of long COVID prevalence when applied to the same pool of participants. Indeed, while some of the estimates of long COVID were as low as 15 percent, others were as high as 42 percent, all based on which definition was applied.
“If every study on long COVID uses a different definition for identifying who has it, the scientific conclusions become harder to compare across studies and may lead to delays in our understanding of it,” Wisk said in the release. “In the absence of an objective measure, like a blood test, or a uniform standard for measuring long COVID, researchers and clinicians will need to decide which definition is best suited for their scientific question and be more transparent about the potential limitations of using a more [versus] less restrictive definition.”
Read More: Treating a Viral Infection in Cats May Solve the Mystery of Long COVID
Difficulties in Diagnosis and Treatment
According to the researchers, the variation wasn’t the only problem with the definitions of long COVID that they tested. In fact, the definitions were also less sensitive and less specific than they ideally would be, suggesting that they didn’t align well with the patient-reported symptoms of the chronic condition. This means that, as they are now, none of the five definitions is an optimal one for a future standard.
Ultimately, Wisk and her colleagues stress that this lack of standardization may lead to an under- or over-estimation of cases of long COVID, and may even stand in the way of future research dedicated to diagnosis and treatment.
“Without a clinically usable and standardized research definition of long COVID, it’s like every study is using a different measuring stick,” Wisk said in the release. “That makes it hard to compare results, develop treatments, or track progress. Without a shared definition, we risk mislabeling patients and misguiding care. This is more than an academic debate — it affects real people.”
This article is not offering medical advice and should be used for informational purposes only.
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