Unusual increase in norovirus outbreaks on cruise ships

Cruise ships present ideal conditions for the spread of Norovirus : With thousands of passengers spending time together in cramped quarters, it may take just one infected passenger or contaminated food to start an outbreak. There has been a noticeable increase in these outbreaks in the first months of 2025.

According to the Vessel Sanitation Program of the US Centers for Disease Control and Prevention ( CDC ), 12 Norovirus cases were recorded in the year as of May 14, 2025. This number is almost equal to the 15 cases recorded in the entire previous year. In 2023, 13 cases were reported. Due to restrictions during the pandemic period, the number of cases was quite low in previous years.

Low immunity and new virus variant may be effective

According to the news in the German Spiegel magazine, experts state that one of the main reasons for this increase is that immunity to a new Norovirus variant has not yet developed sufficiently among the public. In the US in particular, a significant increase in Norovirus cases was observed between August 2024 and June 2025; the number of outbreaks during this period almost doubled compared to the same period the previous year. According to the CDC's criteria, a case is officially recorded if at least 3% of the passengers and crew on a cruise ship show symptoms.

Norovirus: Global and highly contagious

Noroviruses are widespread worldwide and are among the most common causes of acute gastrointestinal infections in humans. The disease manifests itself with sudden onset of severe diarrhea and vomiting, nausea, abdominal pain, headache and weakness. It can cause serious dehydration, which can be life-threatening, especially in children and the elderly.

Norovirus is a highly contagious virus that can be transmitted even in very low doses. There is currently no approved vaccine against the virus.

Cruise ships are the perfect environment for the virus to spread because thousands of people use common areas every day. Outbreaks often begin with a passenger becoming a carrier or handling contaminated items or food.

Epidemics can grow rapidly

The short incubation period of norovirus can lead to multiple waves of transmission during cruises, with outbreaks occurring consecutively on several different cruises on the same ship.

For example, in an outbreak on the luxury cruise ship Queen Mary 2 in March, 266 of 2,538 passengers – or about 11% – were infected, according to CDC data. The infected people were quarantined, and extensive disinfection efforts were carried out on the ship. However, the exact source of the outbreak could not be determined.

Warning to passengers

Authorities are reminding travelers to pay special attention to personal hygiene. The CDC and European health agencies recommend practicing hand hygiene before and during cruise travel, avoiding contaminated foods, and contacting healthcare immediately if symptoms occur.