Screening workers for COVID-19 using temperature scans and questionnaires, the automakers have detected some people who reported for work despite being sick. Some plants have been briefly shut down for disinfection, but so far, there has not been a major outbreak within a U.S. auto plant since most reopened May 18, company and United Auto Workers union officials said.

The risk of an infection picked up outside a plant spreading along assembly lines remains a prime concern, however. An outbreak could shut down a factory costing a manufacturer millions of dollars a day. The disruption caused by the pandemic is creating other challenges as well.