A new study links COVID-19 infection to substantially fewer long-term health problems than previous research suggests.
For the analysis, published in PNAS, researchers led by a team at Stanford University examined 14.4 billion health insurance claims from 244.7 million US patients in the first four months after they tested positive or negative for COVID-19, from March 2020 to March 2021.
The researchers compared health outcomes for those who tested positive with those who tested negative for COVID by polymerase chain reaction (PCR), noting that many other studies have compared test-confirmed COVID patients with groups that included untested controls.
The latter approach “leads to the attribution of future health problems to COVID-19 infection when they might instead be due to non-COVID factors or conditions that prompted the healthcare visit and testing,” they wrote.
COVID-related issues drop sharply after 4 months
The team looked at 614 negative health outcomes across three periods: early, or one to four months post-infection; middle, or five to 12 months after infection; and late, or 13 to 24 months after infection.
When the authors compared people who tested positive for COVID with those who tested negative, they linked 43 symptoms to COVID during the early post-infection period. That was 83.5% less than the 262 health outcomes linked to COVID when they used a comparison group that included untested people.
During the middle period, the number of poor health outcomes linked to COVID fell to five in the test-based design, compared with 286 in the analysis that included untested people. During the late period, no negative health outcomes were linked to COVID in the test-based design, compared with 369 in the analysis including people who hadn’t been tested.
While the number of COVID-attributable health outcomes in the early post-infection period was lower than that in many previous studies, the team found that COVID still affects multiple organ systems, including respiratory, renal, cardiovascular, musculoskeletal, immune, gastrointestinal, neurologic, and dermatologic.
Other illnesses can skew estimates
The researchers found that many people were tested for COVID while seeking care for other illnesses. If those other illnesses later caused health problems, and those people were included in the comparison groups, those health problems may have been mistakenly linked to COVID.
This analysis suggests that while long COVID remains a serious concern, it may have fewer symptoms—and ones of shorter duration and lower overall severity—than previously thought.
By using a study design in which patients were enrolled at the time of their first PCR test, the researchers mitigated many of these biases.
“This analysis suggests that while long COVID remains a serious concern, it may have fewer symptoms—and ones of shorter duration and lower overall severity—than previously thought,” the team wrote.
Source: www.cidrap.umn.edu
