Post-COVID symptoms, prevalence, and time to resolution are different from those seen after flu or pneumonia, better characterizing long COVID, University of Texas investigators say.
The study team analyzed health claims data from Medicare Advantage–covered and commercially insured US adults diagnosed as having symptomatic COVID-19 in 2020 (121,205 patients) and similar groups with flu (20,844) and pneumonia (29,052) diagnosed before the pandemic. Symptoms were evaluated 1, 3, and 6 months after post-diagnosis.
The findings were published yesterday in PLOS One.
Over time, only most severe cases still caused symptoms
After 1, 3, and 6 months post-diagnosis, the odds ratios [ORs] of any symptom in the flu cohort relative to the COVID-19 group were 0.77, 0.77, and 0.68, respectively. In contrast, the respective ORs among pneumonia patients were 2.24, 2.41, and 2.46, meaning more than double the risk at those points in time.
The most common symptoms persisting beyond 4 weeks post-infection among COVID-19 patients were fatigue (25.4%), shortness of breath (24.7%), and joint pain (24.7%). Among flu patients, the most common symptoms were joint pain (19.8%), fatigue (18.2%), and cough (17.7%). In the pneumonia group, shortness of breath (42.2%), fatigue (34.8%), and cough (33.9%) were noted most often.
The odds of having any symptom didn't differ significantly between illness severity levels 4 and 3, but the ORs for severity levels 5, 6, 7, and 8 were 1.12, 1.16, 1.46, and 2.64 times those for severity level 3, respectively.
With increasing time since diagnosis, only the most severe infections (severity levels 7 and 8) continued to cause symptoms. For level 7, the OR of having a symptom versus level 3 was 1.19 and 1.10 after 3 and 6 months, respectively. Likewise, the level-8 OR was 1.84 and 1.53 at the same time points.
Underlying medical conditions resulted in higher odds for all time points and comorbidities. The chronic conditions with the greatest increased odds of symptoms after 4 weeks were rheumatoid arthritis (OR, 2.15), ischemic heart disease (OR, 1.80), and asthma (OR, 1.80).
Magnitude of odds waned, but trend persisted
Overall, relative to patients aged 80 and older, the odds of any symptom after 4 weeks were lower for all age-groups except for 70 to 79 years, which was not statistically different.
We found differences in the prevalence of symptoms as well as different times to resolution better characterizing 'long COVID' and identifying that this persistence of symptoms is unique to COVID-19.
After controlling for demographic factors and chronic conditions, the likelihood of a diagnosis of anxiety, brain fog, fatigue, and shortness of breath after 1, 3, and 6 months rose along with COVID-19 severity. The probability of fatigue for severity level 8 after 4 weeks was 3.32 times that for level 3, and the OR of shortness of breath was 3.07. Over time, the magnitude of ORs ebbed but maintained the trend.
The northeastern United States saw the highest rates of all lingering COVID-19 symptoms, except for headache, for which it had the lowest rates. White patients were more likely to have anxiety or fatigue than their Asian, Black, and Hispanic peers. Hispanic patients were the least likely to have persistent abnormal heart rhythms, brain fog, and shortness of breath.
"We found that COVID-19 symptomology could not be perfectly described by previously seen influenza or pneumonia symptomology," the study authors concluded. "We found differences in the prevalence of symptoms as well as different times to resolution better characterizing 'long COVID' and identifying that this persistence of symptoms is unique to COVID-19."
