It’s a disease humorist Stephen Colbert once poked fun at in this tweet: “Remember, if you’re in public and have the winter vomiting bug, be polite and vomit into your elbow.”

But officials at the California Department of Public Health say a sudden increase in norovirus infections is no laughing matter.

Already, the state has confirmed 32 outbreaks since Oct. 1 — far more than the nine cases reported last year at this time — and officials are warning Californians to wash their hands frequently to guard against infection.

Norovirus, also known as the winter vomiting disease, is a highly contagious virus that causes gastroenteritis, an illness that usually involves vomiting and diarrhea. It is the most common cause of gastroenteritis in the U.S. and is responsible for approximately 20 million illnesses each year, with between 570 and 800 deaths reported annually, health officials said.

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