The US Centers for Disease Control and Prevention (CDC) says a newly dominant strain of norovirus could be to blame for an increase in cases on cruise ships in the first four months of this year.
It has recorded 12 outbreaks on cruise ships so far this year, compared to 18 for the whole of 2024 and 14 in 2023.
While the new dominant strain is currently associated with reported outbreaks on land, cruise ships typically follow the pattern of land-based outbreaks, which are also higher this norovirus season, it said.
The public health body told USA Today: “Norovirus can be especially challenging to control on cruise ships because of the close living quarters, shared dining areas, and rapid turnover of passengers.
“When the ship docks, norovirus can be brought on board in contaminated food or water, or by passengers who were infected while ashore.
“Repeated outbreaks on consecutive cruises may also result from infected crew or environmental contamination.”
A 2021 report by the CDC found that among passengers, acute gastroenteritis incidence rates increased with increasing ship size and voyage length – although there is no new data to suggest the same trend is seen on cruise ships in 2025.
The CDC added: “While the number of recent cruise ship outbreaks has been higher than in years prior to the pandemic, we do not yet know if this represents a new trend.”
Holland America Line, Viking Ocean Cruises II Ltd, Princess Cruises, Royal Caribbean International, Cunard Line, Seabourn Cruise Line and Viking Expedition Operations have all been hit with bouts of norovirus in 2025.
Common symptoms of the stomach bug include diarrhoea, vomiting, nausea and stomach pain.
For the best chance of avoiding the bug, passengers should wash their hands with soap and water, says the public health body.
While norovirus is often associated with cruises, cases onboard ships represent just 1% of all outbreaks reported.
