Experts: Ideal conditions: Norovirus outbreaks on cruise ships on record course

Experts: Ideal conditions Norovirus outbreaks on cruise ships on course for record numbers 06.07.2025, 04:58

Experts are counting almost as many norovirus outbreaks in the first half of the year as in the previous year's total. This may be due to a new variant that is affecting passengers who are still unprotected. At the same time, the travel mode offers the ideal conditions for the gastrointestinal pathogen.

In the first few months of the year, there were an unusually high number of norovirus outbreaks on cruise ships. According to the CDC's Vessel Sanitation Program, 12 outbreaks have already been recorded this year (as of May 14) – almost as many as in the entire previous year. In 2024, 15 outbreaks of gastrointestinal illness were recorded in which norovirus was proven to be the cause, compared to 13 in the previous year. In previous years, the numbers were even lower – due solely to the restrictions imposed during the pandemic years.

Experts cite the still low level of basic immunity in the population against a relatively new, circulating norovirus variant as a possible reason for the high number. In the United States, in particular, there have been a generally high number of norovirus infections recently. Regionally, the number of outbreaks from August 2024 to early June 2025 was almost twice as high as in the same period before.

A cruise ship outbreak appears in CDC data when three percent or more of the ship's passengers and crew show symptoms.

Cruise ships offer ideal conditions

Noroviruses are widespread worldwide and are among the most common causes of acute gastrointestinal illness in humans. Typical symptoms include sudden, severe vomiting and diarrhea, accompanied by nausea, abdominal pain, headache, and general weakness. The disease can lead to dangerous dehydration, especially in children and the elderly.

The pathogen is highly contagious; a person can become infected with just a few virus particles. There is currently no approved vaccine against norovirus. Norovirus has long been associated with cruises: Cruise ships offer ideal conditions for its spread due to the daily use of communal facilities by thousands of people.

Outbreak can escalate quickly

According to experts, one norovirus patient on board, one contaminated object, or one contaminated food item can be enough to trigger an outbreak. The virus has an extremely short incubation period, so there can be multiple waves of infection during a cruise, causing the situation to escalate. There have even been outbreaks on the same ship across multiple cruises.

According to CDC data, for example, there was an outbreak on the "Queen Mary 2" in March, with 266 of the 2,538 passengers (eleven percent) recorded as ill.