Across the country, the litmus test for many children’s entry into school, athletics and extracurricular activities, is their temperature. But experts and medical groups increasingly say that isn’t a good gauge of Covid-19 as many infected children and adults don’t get fevers. Furthermore, variability in individual temperatures as well as questions about the accuracy of body-temperature scanners and infrared contact-free thermometers put such checks at risk of potential error.

In some cases parents are taking their children’s temperatures so often that doctors say they are diagnosing more cases of periodic fever syndrome than usual. Periodic fever syndromes are autoinflammatory disorders in which children have recurrent episodes of fever and other symptoms. Though the genetic conditions are considered rare, doctors say they often go undiagnosed.

In other cases doctors have been stumped by parents who say their otherwise healthy children have had low-grade temperatures for months, unclear if it is connected to an undiagnosed, asymptomatic Covid-19 case or not.