As the number of people reporting persistent, and sometimes debilitating, symptoms from COVID-19 increases, researchers have struggled to pinpoint exactly how common so-called “long COVID” is, as well as how to clearly define exactly who has it or who is likely to get it.
Now, Centers for Disease Control and Prevention researchers have concluded that one in five adults aged 18 and older have at least one health condition that might be related to their previous COVID-19 illness; that number goes up to one in four among those 65 and older. Their data was published in the CDC’s Morbidity and Mortality Weekly Report.
The conditions associated with what’s been officially termed postacute sequelae of COVID-19, or PASC, include kidney failure, blood clots, other vascular issues, respiratory issues, heart problems, mental health or neurologic problems, and musculoskeletal conditions. But none of those conditions is unique to long COVID.
Another new study, published in The Lancet Digital Health, is trying to help better characterize what long COVID is, and what it isn’t.
that could help identify those likely to develop it.
CDC data
The CDC team came to its conclusions by evaluating the EHRs of more than 353,000 adults who were diagnosed with COVID-19 or got a positive test result, then comparing those records with 1.6 million patients who had a medical visit in the same month without a positive test result or a COVID-19 diagnosis.
They looked at data from March 2020 to November 2021, tagging 26 conditions often linked to post-COVID issues.
Overall, more than 38% of the COVID patients and 16% of those without COVID had at least one of these 26 conditions. They assessed the absolute risk difference between the patients and the non-COVID patients who developed one of the conditions, finding a 20.8–percentage point difference for those 18-64, yielding the one in five figure, and a 26.9–percentage point difference for those 65 and above, translating to about one in four.
“These findings suggest the need for increased awareness for post-COVID conditions so that improved post-COVID care and management of patients who survived COVID-19 can be developed and implemented,” said study author Lara Bull-Otterson, PhD, MPH, colead of data analytics at the Healthcare Data Advisory Unit of the CDC.
Pinpointing long COVID characteristics
Long COVID is difficult to identify, because many of its symptoms are similar to those of other conditions, so researchers are looking for better ways to characterize it to help improve both diagnosis and treatment.
Researchers on the Lancet study evaluated data from the National COVID Cohort Collaborative, N3C, a national NIH database that includes information from more than 8 million people. The team looked at the health records of 98,000 adult COVID patients and used that information, along with data from about nearly 600 long-COVID patients treated at three long-COVID clinics, to create three machine learning models for identifying long-COVID patients.
The models aimed to identify long-COVID patients in three groups: all patients, those hospitalized with COVID, and those with COVID but not hospitalized. The models were judged by the researchers to be accurate because those identified at risk for long COVID from the database were similar to those actually treated for long COVID at the clinics.
“Our algorithm is not intended to diagnose long COVID,” said lead author Emily Pfaff, PhD, research assistant professor of medicine at the University of North Carolina at Chapel Hill. “Rather, it is intended to identify patients in EHR data who ‘look like’ patients seen by physicians for long COVID.’’
Next, the researchers say, they will incorporate the new patterns they found with a diagnosis code for COVID and include it in the models to further test their accuracy. The models could also be used to help recruit patients for clinical trials, the researchers say.