Respiratory illnesses like influenza, COVID-19, and RSV are surging across the United States, according to CDC data. Norovirus has also been pegged to a large number of cases in recent weeks. Here's how to protect yourself.

Viral sicknesses have risen in early 2025 amid the ongoing “quad-demic” in the U.S., referring to three respiratory viruses and one gastrointestinal disease, according to the Centers for Disease Control and Prevention (CDC) data.

After the holiday season and an uptick in travel, California faces a rise in respiratory illnesses, prompting health experts to talk of a “quad-demic.” The term refers to the simultaneous spread of four major viruses: COVID-19,