About three-quarters of patients diagnosed with post-COVID conditions did not require hospitalization when they initially became infected, a new study found.

The analysis by Fair Health, a nonprofit group that focuses on health care costs and insurance issues, is among the first that leans on a new medical diagnostic code — “U09.9” — created last year to allow doctors to document long COVID cases.

The study examined the private claims of more than 78,000 people diagnosed with the new code from Oct. 1, 2021, to Jan. 31, 2022. The research, which has not been formally peer-reviewed, was released as a white paper Wednesday.

Post-COVID conditions, or long COVID, are long-term symptoms people experience after becoming infected with the coronavirus, including fatigue, shortness of breath, cough, headache, loss of taste or smell, and cognitive or mental health issues such as anxiety or depression.

“Post-COVID conditions have become an issue of growing national concern,” Fair Health President Robin Gelburd said in a statement. “ … We hope these findings prove helpful for all individuals diagnosed with post-COVID conditions, as well as for providers, payors, policy makers and researchers.”

The researchers found that three in 10 people diagnosed with long COVID had no previous known underlying conditions. 

Thirty-six to 50-year-olds accounted for 34.6% of COVID long-haulers, more than any other age group. The next largest group was 51- to 64-year-olds (31.9%), followed by 23- to 35-year-olds (17%). Patients 22 and younger made up 10.5% of the cases.

Individuals 65 and older accounted for just 6% of the cases, but the paper’s authors noted that a limitation of the study was that they did not have data from patients covered by most Medicare plans. Other researchers have found that long COVID is more likely with increasing age.

The most common conditions across all age groups and genders were breathing problems, coughing and fatigue. But some diagnoses were more common in some age groups than in others, including multisystem inflammatory syndrome in infants to 12-year-olds, heartbeat abnormalities in 13- to 22-year-olds, generalized anxiety disorder in 23- to 35-year-olds and hypertension in 65 and older. 

The study also found that females were more likely to be diagnosed with post-COVID conditions than males — 60% compared to 40%. 

The percentage of females in the study who had never been hospitalized with COVID also was higher. Eighty-two percent were not admitted to hospitals, while about two-thirds of men had not been.

The researchers calculated the average increase in Department of Health & Human Services-Hierarchical Condition Category risk scores — a metric that aims to identify which patients are likely to consume more health care resources in the future and incur greater care costs long-term. In general, an individual with a score lower than 1.0 is considered relatively health. But long COVID contributed to increasing patients’ scores by 1.02 points on average — and those ages 65 and older saw their scores climb by 1.80 points.