What to know about 'quad-demic' of COVID, flu, RSV and norovirus in US The U.S. is seeing a "quad-demic" as cases of COVID-19, flu, RSV and norovirus spread at the same time. Experts said this is what you need to know. ABC News ABC News

Four viruses are currently circulating in the United States, which some have referred to as a "quad-demic."

Data from the Centers for Disease Control and Prevention showed an increase in three respiratory viruses—COVID-19, flu and RSV—and the gastrointestinal disease norovirus.

Emergency department visits are "high" and "very high" for flu and RSV, respectively, and "elevated" for COVID-19 across the U.S., according to the CDC.

...