Norovirus appears to be at a seasonal high, according to data from the Centers for Disease Control and Prevention.

The rate of positive results for norovirus tests, averaged over three weeks, topped 15% at the end of last week. That is the highest on record since late March 2022.

Norovirus is sometimes called the stomach flu, but it is not related to the influenza virus. Rather, it is a highly contagious virus that typically causes gastrointestinal symptoms such as diarrhea, vomiting, nausea, and stomach pain. You may also have a mild fever and aches.

Just a few virus particles are enough to make someone sick, and they spread easily through hands, surfaces, food, and water. An infected person can transmit the virus for days after feeling better, potentially up to two weeks, according to the CDC.

At the regional level, the The Midwest had the highest average rate of test positivity for norovirus as of Saturday, by more than 19%, higher than any other week in the past year.

The CDC did not immediately respond to a request for additional information on current norovirus rates.

The agency tracks norovirus outbreaks through a network of 14 state health departments. Although network data is delayed, your most recent count suggests that state health departments reported 25 outbreaks as of the first week of January, the most since May. Between August and early January, a total of 225 norovirus outbreaks were reported to CDC, compared to 172 during the same period last season.

Norovirus is the leading cause of foodborne illness in the country. Food can become contaminated if fruits or vegetables are grown or washed with contaminated water. Oysters also pose a norovirus risk if harvested from contaminated water. In December, a multistate outbreak was linked to raw oysters from Texas, with nearly 300 norovirus cases reported.

Most norovirus outbreaks in the US occur between November and April. On average, the country sees about 20 million cases per year, with nearly 110,000 hospitalizations and 900 deaths, mostly among people 65 and older.

There is no treatment for norovirus, but the CDC recommends drinking plenty of fluids to prevent dehydration. The disease usually resolves in a few days.

In England, norovirus rates this year are exceptionally high, according to the UK Health Security Agency. As of late January, norovirus laboratory reports were 66% higher than the average for the five seasons prior to the covid pandemic. The agency primarily attributes the increase to higher reporting among people 65 and older.