OTTAWA — For most people, the pandemic has turned border crossing into an impossibility. But for Laurie Dufresne, who lives in Canada and works in the United States, it remains part of her daily commute.

Ms. Dufresne is one of about 1,600 nurses and other health care workers who leave Windsor, Ontario, a city of 217,000, for daily work in Detroit, a metropolitan area of more than four million people. In Windsor, infections remain comparatively under control. Detroit, though, has one of the most severe coronavirus outbreaks in the United States.

For health workers like Ms. Dufresne, fulfilling desperately needed medical duties across the border means being in an uncomfortable position. Canadian officials have been blunt about the risks, and health workers have found themselves under scrutiny at home as potential vectors of the pathogen, not just to Windsor but to all of Canada, which so far has not been hit as hard as the United States.

In other countries, health care workers have also found themselves grappling with a community afraid they will spread the virus when they leave their hospitals to come home.