The highly contagious norovirus is spreading rapidly across the US as the year ends. A new variant, GII.17, is driving this surge. This wave of norovirus outbreaks comes along with rising flu, whooping cough, measles, and COVID cases nationwide. Known as the 'winter vomiting disease,' norovirus causes vomiting and diarrhoea and can be dangerous for the elderly, children, and people with weak immunity, Axios reported. California has seen a sharp climb in cases, especially in San Francisco and Los Angeles. Other states like Michigan, New Jersey, North Carolina, Texas, Oklahoma, Colorado, Alabama, Montana, and Wyoming have also reported more cases, according to Epic Research data. The Centers for Disease Control and Prevention (CDC) said the national positivity rate jumped from 9.9% in the week ending Dec. 9 to 12.11% by Dec. 13. Norovirus causes inflammation of the stomach and intestines. Symptoms start 12 to 48 hours after infection and include diarrhoea, vomiting, nausea, stomach pain, and dehydration. Fever and body aches can happen but are rare, per CDC. There is no specific treatment, but most people recover in one to three days by resting and staying hydrated, says the Cleveland Clinic. The CDC found that outbreaks from the GII.17 variant rose dramatically from 7.5% in 2022–23 to 75.4% in 2024–25. Meanwhile, outbreaks from the older version, GII.4, fell from 49% to 10.7%. Alongside norovirus, COVID cases are rising in 31 US states, many fueled by the XFG Stratus variant. Europe is also facing a new flu outbreak linked to a summer version of H3N2. Health officials advise washing hands well and disinfecting surfaces because hand sanitizer alone doesn't stop norovirus. People infected with norovirus should avoid preparing food for a few days to stop spreading the virus.