‘Speed is critical’: As coronavirus spreads in U.S., officials face daunting task of tracing case contacts

This weekend, as it became clearer and clearer that Covid-19 has been spreading stealthily through the Pacific Northwest, the task facing health officials has become more and more monumental. To try to stop the virus’ transmission and restrain the outbreak, they need to identify every single person with whom patients have come into contact, isolate those at risk of harboring the illness, and monitor the entire network of people for symptoms.

That’s hard even if you know how each patient became infected. If you don’t, it can be downright herculean. The fact that the pathogen is passing through people without making them sick enough to seek care means that they may have unwittingly transmitted it for weeks before it came to the attention of authorities.