An observational study of more than 2 million Medicare beneficiaries aged 65 and older finds that symptom-based testing identified long COVID in 30% of hospitalized patients and 17% of outpatients. Established diagnostic codes captured only 2.6% and 0.49% of those cases, respectively.
The study was published yesterday in PLOS Medicine.
Researchers with the National Institutes of Health used International Classification of Diseases, 10th revision (ICD-10), diagnostic codes to identify cases of COVID-19 and influenza. They used the designated long-COVID code or any of the 11 symptoms included in the World Health Organization (WHO) definition to identify long-COVID cases 1 to 3 months after infection.
Identification of persistent flu symptoms (long flu) for the 2018 and 2019 flu seasons using the same symptom-based definition for long COVID.
Long COVID tied to more severe outcomes
Of 2,071,532 patients who tested positive for COVID-19 from April 2020 to June 2021, the symptom-based definition identified long COVID in 16.6% of hospitalized patients and 29.2% of nonhospitalized patients. The ICD code, however, identified only 2.6% and 0.49%, respectively, of those cases. Of 933,877 flu patients, 24.6% of hospitalized patients and 17.0% of outpatients conformed to the long-flu definition.
Relative to long-flu patients, those with long COVID had higher rates of shortness of breath, fatigue, heart palpitations, loss of smell or taste, and neurocognitive symptoms. Nonhospitalized long-COVID patients had higher odds of any-cause hospitalization (31.9% vs 26.8%; odds ratio [OR], 1.06) and more outpatient visits than long-flu outpatients (average, 2.9 vs 2.5; incidence rate ratio, 1.09).
Relying on specific long COVID diagnostic codes results in significant underreporting.
Long-COVID patients visited an emergency department (ED) less often than long-flu patients, likely because ED usage in general was lower than normal during the study period.
"Relying on specific long COVID diagnostic codes results in significant underreporting," the study authors wrote. "The impact of long COVID on healthcare utilization is higher than long Flu."