What is the 'vomit bug' spreading across the US? Everything to know about the highly contagious stomach virus

The 'vomit bug,' or norovirus, is causing outbreaks across the US, especially in California. Symptoms arise within 12 to 48 hours and may lead to dehydration.

A highly contagious stomach virus commonly known as the "vomit bug" is spreading throughout the majority of the United States, including Southern California, where hikers have recently reported experiencing symptoms, according to the Pacific Crest Trail Association (PCT).

The 'vomit bug,' or norovirus, is causing outbreaks across the US, especially in California. Symptoms arise within 12 to 48 hours and may lead to dehydration. (Unsplash)

A norovirus outbreak in the San Francisco Bay Area was also reported by Dr Linda Yancey, an infectious disease specialist at Memorial Hermann, to NBC on Friday.

The virus, which is the leading cause of foodborne illness in the US, has sparked concern because of its ability to spread quickly through contaminated food, water, surfaces, and close person-to-person contact.

What is the vomit bug?

The vomit bug, or Norovirus, is not a new disease, but periodic spikes in infections often occur when highly transmissible strains circulate through communities. It is a highly infectious virus that causes acute gastroenteritis, an inflammation of the stomach and intestines. The illness is commonly referred to as the stomach flu.

Yancey assured, "There really isn't anything unusual about this one in California. They were simply unlucky."

The Center for Disease Control (CDC) reported that the virus spreads through direct contact with infected individuals, contaminated food and beverages, or by touching contaminated surfaces and then touching the mouth.

According to health experts cited by People, the virus can infect people of all ages and is notorious for causing sudden outbreaks in schools, nursing homes, hospitals, restaurants, and cruise ships.

Reports from wastewater surveillance, according to NBC, show that norovirus levels are "high" in numerous regions of the nation, with a discernible rise in the Northeast.

WastewaterSCAN's scientific program manager, Amanda Bidwell, told PEOPLE, “At the national level, norovirus is still in the HIGH category due to high concentrations over the last 21 days.”

From August 1, 2025, to May 7, 2026, "1,194 norovirus outbreaks were reported by NoroSTAT-participating states," according to statistics from the CDC's NoroSTAT program.

What are the symptoms of the vomit bug or Norovirus?

Norovirus symptoms usually appear between 12 and 48 hours after exposure. The most common symptoms include

• sudden vomiting
• nausea
• diarrhea
• stomach cramps
• general fatigue.

In rare cases, some people may also experience fever, headaches, chills, and body aches.

According to Mayo Clinic, for most healthy individuals, symptoms improve within one to three days. However, dehydration remains the biggest concern, especially for children, elderly adults, and those with underlying health conditions.

Medical experts recommend drinking fluids regularly and seeking medical attention if severe dehydration develops. A man was taken to the hospital after several hikers on the Pacific Crest Trail in California became dehydrated and felt "weak" due to the norovirus outbreak, PEOPLE previously reported.

CDC, on their Norovirus awareness page, recommend frequent handwashing with soap and water, thorough cleaning of contaminated surfaces, proper food handling, and avoiding food preparation while sick.