The man administering tests at the site, run by a company called O’Hare Clinical Lab Services, was wearing jeans and a leather jacket, not medical scrubs or a gown. He moved among the cars without changing gloves, she said. He asked for her driver’s license but not her insurance card.

But Alexander was feeling ill and desperate to make sure she didn’t pass covid-19 to her husband, a kidney transplant recipient. The rapid test came back negative that day, Dec. 23, providing temporary relief, she said.

Five days later, still sick, she went to a hospital. The test there came back positive. Her husband soon fell ill, too. He was hospitalized with covid-19 in mid-January and has remained on a ventilator since then, Alexander said.

While false negatives occur on antigen tests, Alexander now believes the first test was wholly unreliable.