All of the 91 US cruises currently at sea have confirmed or suspected COVID-19 on board, the CDC says

• All 91 US cruises currently at sea have at least one COVID-19 case on board, according to the CDC.
• They're all being either investigated or observed by the CDC.

All 91 US cruises currently at sea have confirmed or suspected COVID-19 cases on board, according to the Centers for Disease Control and Prevention (CDC).

The figure comprises cruise ships carrying passengers that are currently in US waters or set to enter them, and includes vessels operated by Carnival, Princess, Disney, Royal Caribbean, and Norwegian.

The CDC said it had investigated all 91 ships and is keeping them under observation, save for two where the agency's probes were at an earlier stage.

Cruise ships have been a hotbed for outbreaks of COVID-19 since the start of the pandemic and the CDC recommends that all travelers avoid cruises regardless of vaccination status. The probability of getting COVID-19 on a cruise ship is "very high," even for passengers with booster shots, the CDC said.

Meanwhile, cruise lines are canceling voyages amid rising coronavirus cases among passengers and crew.

Norwegian said Tuesday that it was cutting short a voyage that departed from Miami on Monday "due to Covid-related circumstances." CBS Miami reported there was a COVID-19 outbreak among the crew of the ship, which was destined for an 11-day round-trip via the Panama Canal.

On Wednesday, Norwegian canceled a nine-day Caribbean cruise scheduled to set sail later that day, again citing factors related to the coronavirus.

It's also canceled some other upcoming cruises, including some as far ahead as April, "due to ongoing travel restrictions."

Norwegian says that all crew and passengers have to be vaccinated against COVID-19. Guests also are tested before boarding the ship and have to wear masks on board.

All 91 US cruises are "yellow" status

All 91 ships the CDC has under observation or is investigating have been assigned "yellow" status by the agency, per data collected Wednesday and published Thursday. This means that at least 0.1% of passengers are believed to be infected – including cases reported in passengers within five days of leaving the ship – or that at least one crew member is infected.

The CDC defines a "COVID-19 case" as a person with a positive COVID-19 test. The definition also includes people with COVID-19-like illnesses who refuse to get tested, test negative for COVID-19 but weren't confirmed to have any other respiratory illnesses, had inconclusive test results, or weren't able to get tested due to a lack of resources on board.

Yellow status means a ship has met the threshold for a CDC investigation. Ships can also be assigned yellow status if they fail to submit certain data on time.

The Washington Post reported that the CDC's Tuesday update marked the first time all US cruises with passengers had been assigned at least yellow status.

A Carnival spokesperson previously told Insider that the CDC had been "fully informed and supportive of its protocols and operational plans."

Of the 19 US cruises at sea with just crewmembers on board, three had yellow status, meaning the CDC was investigating. Ten had green status, meaning the ship had no reported cases of COVID-19. Six had orange status, meaning fewer than 1% of staff had COVID-19 and the CDC wasn't investigating.

The CDC's cruise database only includes foreign-flagged cruise ships operating or planning to operate in US waters, and US-flagged cruise ships that choose to participate voluntarily.