Government

The C.D.C. changes testing guidelines to exclude those exposed to virus who don’t exhibit symptoms.

The Centers for Disease Control and Prevention quietly modified its coronavirus testing guidelines this week to exclude people who do not have symptoms of Covid-19 — even if they have been recently exposed to the virus.

Experts questioned the revision, pointing to the importance of identifying infections in the brief window immediately before the onset of symptoms, when many individuals are thought to be most contagious.