University of California, Los Angeles, researchers said in a study published in the Journal of General Internal Medicine.
The UCLA researchers studied 1,038 people enrolled in the UCLA COVID Ambulatory Program between April 2020 and February 2021 and found that 309 developed long COVID.
A long-COVID diagnosis came if a patient answering a questionnaire reported persistent symptoms 60-90 days after they were infected or hospitalized. The most persistent symptoms were fatigue (31%) and shortness of breath (15%) in hospitalized participants. Among outpatients, 16% reported losing sense of smell.
The study’s findings differ from earlier research. The University of California, Davis, for example, estimated that 10% of COVID-19 patients develop long-haul symptoms. A 2021 study from Penn State University found that more than half of worldwide COVID-19 patients would develop long COVID.
Part of the discrepancy can blamed on the fact there is no official, widely accepted definition of long COVID. The Centers for Disease Control and Prevention has said it means patients who experience “new, returning, or ongoing health problems 4 or more weeks after an initial infection” the coronavirus. The UCLA study, meanwhile, included patients still having symptoms 60-90 days after infection.
Still, the UCLA research team looked at demographics and clinical characteristics in an attempt to develop effective treatments.
People with a history of hospitalization, diabetes, and higher body mass index were most likely to develop long COVID, the researchers said. The kind of insurance the patients had also seemed to be a factor, though the researchers didn’t offer a reason why.
“Surprisingly, patients with commercial insurance had double the likelihood of developing [long COVID] compared to patients with Medicaid,” they wrote. “This association will be important to explore further to understand if insurance status in this group is representing unmeasured demographic factors or exposures.”
Older age and socioeconomic status were not associated with long COVID in the study – a surprise because those characteristics are often linked with severe illness and higher risk of death from COVID-19.
Weaknesses in the study included the subjective nature of how patients rated their symptoms and the limited number of symptoms evaluated.
“This study illustrates the need to follow diverse patient populations ... to understand the long COVID disease trajectory and evaluate how individual factors such as preexisting comorbidities, sociodemographic factors, vaccination status and virus variant type affect type and persistence of long COVID symptoms,” said Sun Yoo, MD, health sciences assistant clinical professor at UCLA.
A version of this article first appeared on WebMD.com.