Long COVID symptoms acquire firmer definition, threshold for diagnosis

After examining nearly 10,000 patients, most of whom had COVID-19, researchers have outlined 12 symptoms that most set apart those with and without long COVID, the post-infection set of conditions that can affect nearly every tissue and organ in the body.

The 12 symptoms found are: post-exertional malaise, fatigue, brain fog, dizziness, gastrointestinal symptoms, heart palpitations, issues with sexual desire or capacity, loss of smell or taste, thirst, chronic cough, chest pain, and abnormal movements.

The research team also found that long COVID was more common and severe in study participants infected before the 2021 Omicron variant.

The study, coordinated through Researching COVID to Enhance Recovery (RECOVER) initiative of National Institutes of Health (NIH), US, examined data from 9,764 adults, including 8,646 who had COVID-19 and 1,118 who did not have COVID-19.

The findings are published in the Journal of the American Medical Association (JAMA).

Based on patient-reported symptoms, the researchers established a scoring system. They gave each patient a score based on symptom combinations after assigning points to each of the 12 symptoms. Thus, they identified a meaningful threshold for identifying participants with long COVID.

They also found that certain symptoms occurred together and defined four subgroups or "clusters" with a range of impacts on health.

In addition to establishing the scoring system, the researchers found that participants who were unvaccinated or who had COVID-19 before the Omicron strain emerged in 2021 were more likely to have long COVID and more severe cases of long COVID.

Based on a subset of 2,231 patients in this analysis who had a first COVID-19 infection on or after Dec. 1, 2021, when the Omicron variant was circulating, about 10 per cent experienced long-term symptoms or long COVID after six months.

Further, reinfections were also linked to higher long COVID frequency and severity, compared to people who only had COVID-19 once.

"This study is an important step toward defining long COVID beyond any one individual symptom," said study author Leora Horwitz, director of the Center for Healthcare Innovation and Delivery Science, US, and co-principal investigator for the RECOVER Clinical Science Core, at NYU Langone Health, US. "This approach, which may evolve over time, will serve as a foundation for scientific discovery and treatment design."

The researchers explained that studying the underlying biological mechanisms of long COVID is central to advancing informed interventions and identifying effective treatment strategies.