• The CDC randomly inspects and scores cruise ships to prevent the spread of stomach viruses.
• The average score of vessels in 2024 is 95.9 out of 100 — 85 or less is considered failing.
• The nine dirtiest ships scored between 86 to 89. Two others failed but passed in later reviews.

A "B" is considered a passing grade on most exams.

For cruise ships, scoring an 85 out of 100 on the Centers for Disease Control and Prevention's Vessel Sanitation Program review is considered a failure.

In 2024, the CDC reported 13 bacterial and viral outbreaks on ships. Most incidents were of norovirus, a highly contagious bug that quickly spreads through tainted food, water, surfaces, or people.

Best not to be a victim. Its main symptoms — vomiting, diarrhea, nausea, and stomach pain — can quickly ruin a vacation.

To mitigate these outbreaks, the CDC conducts random and unannounced sanitary inspections on cruise ships. The public health agency then scores the vessel from zero to 100, with outcomes of 85 or lower considered inadequate.

The review includes checking common spaces like pools and children's activity centers. Obvious issues like vermin and improperly stored food will cost points. As will subtler problems, such as buffet handwashing stations with lights less than 110 lux and produce stickers left where cleaned cooking equipment is stored.

The CDC has performed 151 inspections in 2024, including repeat inspections on 23 ships. The average score is about 95.9. 27 vessels achieved perfect marks, while two failed but later passed in later reviews.

Nine vessels didn't break into the 90s range, including Ritz-Carlton Yacht Collection's ultra-luxury Evrima:

1. Hanseatic Inspiration — Hapag-Lloyd Cruises, scored 89 (inspected October 28, previously received a 62 on September 29)
2. Carnival Elation — Carnival Cruise Line, scored 89 (inspected March 14)
3. Adventure of the Seas — Royal Caribbean International, scored 89 (inspected January 23)
4. National Geographic Sea Bird — Lindblad Expeditions, scored 88 (inspected July 25)
5. Carnival Miracle — Carnival Cruise Line, scored 88 (inspected April 21)
6. MSC Magnifica — MSC Cruises, scored 86 (inspected May 17)
7. Evrima — Ritz-Carlton Yacht Collection, scored 86 (inspected February 9)
8. Carnival Breeze — Carnival Cruise Line, scored 86 (inspected March 21)
9. Caribbean Princess — Princess Cruises, scored 86 (inspected March 20)

Crystal Serenity received an 89 on February 2 but was bumped to a 90 seven months later. Similarly, Margaritaville at Sea Paradise received a failing score of 83 on May 1 but passed a subsequent inspection with a 92 on July 2.

What the cruise lines have said

A spokesperson for Hapag-Lloyd told Business Insider that Hanseatic Inspiration's initial lower score was a "very unfortunate incident" that didn't reflect the company's operational standards. "We have been consistently meeting strict hygiene requirements worldwide for many years with exemplary results," they said.

Following the inspection, the cruise line addressed the ship's "operational aspects" to meet its quality standards, as showcased in the vessel's follow-up passing score in October.

The spokesperson said lingering issues are "being addressed and will be completed in a timely manner," and the company will continue to improve its "quality management processes" particularly with regard to the requirements of the CDC."

Similarly, a spokesperson for MSC Cruises told BI in October it had implemented an "improvement plan" on MSC Magnifica according to the CDC inspector's suggestions. Many of the changes were immediate and only needed "minor" efforts, it said. The cruise line said that it believes Magnifica's score "is not a true reflection of the ship as it is today" and would "welcome any future inspection."

MSC noted that many of its ships frequently achieve above 90, including the MSC Meraviglia and MSC Seashore, which both received perfect marks in 2024.

Carnival, Royal Caribbean, Lindblad Expeditions, the Ritz-Carlton Yacht Collection, and Princess Cruises didn't respond to a request for comment.