Recently, I’ve chatted with a handful of Coloradans who believe they had COVID-19 well before the state confirmed its first cases on March 5. Their stories, and the earnestness with which they tell them, can be pretty damn convincing: It’s the sickest I’ve ever been. I had all the symptoms. My flu test was negative.

Some of these folks are so assured they were already infected last winter—and are therefore now immune—that they’re bucking public health guidelines. One middle-aged man from Woodland Park, for instance, told me he would “hug anyone” right now.

When I hear these impassioned testimonies, a part of me can’t help but feel jealous. I’ve been various degrees of stressed about the virus since March, and it’d be incredibly relieving to believe, wholeheartedly, that I was bulletproof. But another part of me feels skeptical. There’s so much still unknown about COVID-19, and without a positive test result, how can one be so sure of infection?

So I spoke with David Bortz, mathematical biologist at the University of Colorado Boulder and a member of the state’s COVID-19 modeling team. Turns out, trying to determine how likely it is that someone was infected by COVID-19 without testing is a very challenging question to answer conclusively, Bortz says.

Here’s what we do know: State health officials announced Colorado’s first cases of COVID-19 on March 5. But the new coronavirus likely arrived here sometime in January, according to an analysis by Bortz and his colleagues. It first appeared among international tourists in ski resort towns, including Vail and Aspen, and the January prediction, Bortz explains, is based on models that account for the virus’s incubation period, average doubling time, and data from other countries which suggests that in the early stages of the epidemic only 15 percent of all cases were actually identified. 

So, if you were sick in January, does that mean COVID-19 was to blame? Probably not. Unless you visited Vail or Aspen in January, says Bortz, it’s extremely unlikely that you had COVID-19 that month. And even if you did visit those places in January and then developed flu-like symptoms three to 14 days later, it’s still unlikely that you were ill with COVID-19, he adds. There may have been COVID-19 transmission in January in other areas of Colorado, Dr. Rachel Herlihy, state epidemiologist, told 5280 through emailed correspondence with a spokesperson. But these cases, which involve counties on the Front Range, mountain, and northeast areas of Colorado, are still being investigated. As for everyone that felt like crap before the new year? Sorry, but it doesn’t seem possible that the virus was in Colorado that early, says Bortz.

If you were under the weather in February, well, that’s when things get murky. Because of limited data and uncertainty surrounding the virus’s spread, it would be extremely challenging, per the state’s COVID-19 modeling team, to make conclusions on the likelihood that illnesses in February were indeed the novel coronavirus.

But it may help to remember that winter is flu season—and flu and COVID-19 have many similar symptoms, as do other respiratory infections, Herlihy said.

Herlihy points to the peak of test positivity in Colorado, which occurred in mid-April when the state assumed most people were seeking tests because they had symptoms consistent with COVID-19.  Yet at that peak, only 22 percent of people who got tested had positive results, which means 78 percent of those tested—the large majority of whom are assumed to have had COVID-like symptoms—ultimately did not test positive.

Also worth noting: A modeling team at the Colorado School of Public Health estimates that approximately 280,000 people in Colorado have been infected to date (only about 57,000 have tested positive), per information shared by Herlihy on August 25. That’s a lot of people, to be sure, but it’s only 4.8 percent of the state’s total population—meaning an estimated 95.2 percent of Coloradans have not yet been infected with COVID-19.

The bottom line: “People should not assume they were infected by COVID-19 unless they had a test documenting that they were positive,” Herlihy noted. And even if you do have a positive result (whether from a viral swab or an antibody test), it doesn’t mean you are protected from reinfection or that you should stop following prevention practices—especially as we head into flu season.

Just last week, researchers announced a study identifying the first case of COVID-19 reinfection in the U.S—but the material has not yet been reviewed by outside experts and researchers believe reinfection is probably rare, according to Reuters.  

Amidst all this uncertainty, it makes sense that Coloradans—like the ones I’ve encountered—are earnestly seeking more definitive truths. Even Bortz, who had a cold in January, says he wondered, at one time, if his illness had been COVID-19. “It’s a natural thing to think about,” he says. 

He knows now, however, that it’s “pretty unlikely” he had the new coronavirus in January. 

And this unsettling reality—where “unlikely,” “probably,” and “maybe” trump more comforting absolutes—is one, it seems, we’ll all have to live with a while more.