In the winter months, it seems few are safe from some kind of illness — flu, COVID-19, norovirus, colds. While many of the germs that cause this misery can circulate throughout the year, scientists think that the winter surge of flu and cold activity may be because we spend more time indoors and the cold,

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,