‘Important questions remain’
Commenting on the finding, Aravind Ganesh, MD, DPhil, a neurologist at the University of Calgary (Alta.), said that by including control populations, the study addressed an important limitation of previous research. Dr. Ganesh, who was not involved in the study, said that the controls help to determine the cause of associations found in other studies, including his own research on long-term symptoms following outpatient care for COVID-19.
“I think what this tells us is that maybe a lot of the issues that we’ve been seeing as complications attributable to COVID are, in fact, complications attributable to serious illness,” said Dr. Ganesh. He also found the association with venous thromboembolism interesting because the condition is recognized as a key risk factor for COVID-19 outcomes.
Compared with smaller randomized control trials, the population-level data provided a much larger sample size for the study. However, this design comes with limitations as well, Dr. Ganesh noted. The study relies on the administrative data of diagnostic codes and misses symptoms that aren’t associated with a diagnosis. In addition, because the cohorts were not assigned randomly, it may not account for preexisting risk factors.
While the study demonstrates associations with physical and mental health conditions, the cause of postacute effects from COVID-19, influenza, and sepsis is still unclear. “Important questions remain,” said Dr. Ganesh. “Why is it that these patients are experiencing these symptoms?”
The study was supported by ICES and the Canadian Institutes of Health Research. Dr. Quinn reported part-time employment at Public Health Ontario and stock in Pfizer and BioNTech. Dr. Ganesh reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.