Norovirus outbreaks are on the rise around the country and on cruise ships

The Cunard cruise liner RMS Queen Mary 2 was among several ships to see an outbreak of vomiting and diarrhea caused by norovirus this winter. Loic Venance/AFP via Getty Images hide caption

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Loic Venance/AFP via Getty Images

Nearly 900 people aboard cruise ships were sickened from gastrointestinal disease in December amid an escalation in both the frequency and severity of outbreaks, according to data from the Centers for Disease Control and Prevention.

So far this year, there have been 16 outbreaks on cruise ships, from norovirus, salmonella, e. coli or other unidentified pathogens that cause gastrointestinal symptoms such as diarrhea or vomiting. That's the largest number of cruise ship outbreaks in 12 years.

Five of those outbreaks occurred this month. The most recent incident involved the British ocean liner Queen Mary 2, where nearly 13% of passengers and over 5% of crew aboard were infected.

This is happening amid a nationwide surge of norovirus, a fast-moving virus often transmitted through fresh food or water contaminated with tiny particles of infected feces or vomit. It can also be transmitted through surfaces and human contact, with most outbreaks happening in places like hospitals, restaurants, and long-term care facilities.

During the week of December 5 — the most recent time period for which data is available — the CDC reported 91 suspected or confirmed outbreaks of norovirus, which is higher than the range reported during the same period in previous seasons since 2012. The data comes from 14 states that report to the CDC's National Outbreak Reporting System.

"This year the number of reported norovirus outbreaks have exceeded the numbers that we've seen recently and in the years before the pandemic," the CDC said in a statement.

Each year there are about 2,500 norovirus outbreaks, according to the CDC, and they're usually more common in cooler winter months. It's not known why the illness spreads more in winter, though scientists speculate it may be because people spend more time together indoors.

Norovirus outbreaks declined in the 2020-21 season because of curtailed social activities and transmissions during the pandemic.

A CDC reporting system that gathers testing data from labs around the country shows a rate of 22% positive norovirus tests for the week ending Dec. 21, which is the highest rate since 2018.

Young children and older adults are most at risk from severe dehydration from norovirus. The illness leads to some 465,000 emergency department visits each year, mostly in young children.

The disease usually spreads through direct contact, such as sharing food or utensils. To prevent infection, the CDC recommends keeping up with handwashing , "especially for people who handle food or are around children, older adults, or people with weakened immune systems."

Norovirus is a hardy virus that the CDC says can persist on surfaces for days or weeks. Recent infections on ships have prompted the Queen Mary's parent company, Cunard, and other cruise lines, including Holland America, to increase cleaning and sanitation of ships, as well as to isolate sick crew members.

The measures include "additional deep cleaning of public areas and staterooms, and close monitoring by our medical team, to ensure the comfort, health, and wellbeing of all guests and crew," Cunard North America spokesperson Jackie Chase said in an emailed statement.

Holland America Line, which had norovirus outbreaks on two of its ships this month, says it sanitized both ships and has not had further outbreaks.