The top U.S. infectious disease expert said the country faced a "whole lot of trouble" if it did not encourage universal wearing of face masks and avoid mass gatherings.

The rise in infections, deaths and hospitalizations over the summer was blamed in part on Americans behaving heedlessly over Memorial Day and July Fourth.

In an interview with Global News, Dr. Anthony Fauci explains why he is worried about coronavirus cases spiking in the fall.

Fauci, the 79-year-old director of that institute, has tested negative for COVID-19 and he will continue to be tested regularly, the official said in an emailed statement.