Melissa Pinto, a co-author of the latter study and associate professor in the Sue & Bill Gross School of Nursing at University of California Irvine, says the researchers examined healthcare records of people who tested positive for COVID-19 but hadn’t reported symptoms at the time of infection—only to come in later with symptoms associated with long COVID-19. To ensure they were identifying long-haulers, the researchers screened out anyone with a preexisting illness that could explain their later symptoms.
“This is not from another chronic disease,” she says. “These are new symptoms.”
But it’s unclear how accurate any of these estimates might be. Pinto says that some long-haulers are wary of seeking care after having their symptoms dismissed by physicians who weren’t familiar with long COVID-19 syndrome. That’s why she believes that the rates of asymptomatic infections among long-haulers are an underestimate.