The short version
- CDC posted 23 cruise ship gastrointestinal outbreaks in 2025, up from 18 in 2024 and 14 in 2023; norovirus caused 18 of the 23[5][6].
- Where specimens were tested in 2008 to 2014, 97% of ship outbreaks were norovirus[10].
- Alcohol hand sanitizer does not work well against norovirus; soap, water and bleach at 1,000 to 5,000 ppm do[3].
- The master of any ship bound for a US port must report ill persons to CDC, and cruise ships must file a gastrointestinal case count 24 hours before arrival[8].
How often does norovirus hit ships?
CDC’s Vessel Sanitation Program posts an outbreak when 3% or more of passengers or crew on a ship under its jurisdiction report gastrointestinal symptoms[4]. The posted counts have risen every year since 2023.
| Year | Outbreaks posted | Caused by norovirus |
|---|---|---|
| 2023[6] | 14 | 13 (93%) |
| 2024[5] | 18 | 15 (83%) |
| 2025[5] | 23 | 18 (78%) |
| 2026, sailings to 20 July[4] | 9 | 5; 2 E. coli, 2 unknown |
The program covers ships that carry 13 or more passengers on a foreign itinerary with US ports[7]. Cargo ships, workboats and domestic passenger vessels are outside these counts, so their outbreaks go unpublished, not unseen.
What the long-run data shows
| Study | Scope | Key finding |
|---|---|---|
| Freeland et al., 2016[10] | Cruise ships, 2008 to 2014 | 133 outbreaks; 92 of 95 tested (97%) norovirus; crew rate flat at 21.3 to 21.6 per 100,000 travel days |
| Jenkins et al., 2021[11] | 37,276 voyages, 252 ships, 2006 to 2019 | Crew rate fell from 13.5 to 5.2 per 100,000 travel days; highest on extra-large ships |
| Mouchtouri et al., 2024[12] | 45 cruise outbreaks, 1990 to 2020 | Average attack rate 7% in passengers, 2% in crew; person-to-person spread in 35 of 45 |
| Riddle et al., 2006[13] | 44 US Navy ships, 2000 to 2001 | 3.3 possible outbreaks per 100 ship-weeks, lasting 4.4 weeks on average |
The Navy data matters for operators outside the cruise trade: a closed crew with shared galleys and berths behaves like a cruise ship, just without the published statistics[13].
Why it spreads so fast on board
Symptoms start 12 to 48 hours after exposure and most people recover in 1 to 3 days[2]. The virus can be shed before symptoms begin and stay in stool for two weeks or more after recovery[3].
In the 2024 review, sharing a cabin with an ill person raised the odds of illness more than 38 times, and person-to-person spread drove most outbreaks[12]. The US carries 19 to 21 million norovirus illnesses a year, so the virus boards with crew and passengers at every port[1].
What US law requires
| Rule | What it requires |
|---|---|
| 42 CFR 71.21(a)[8] | The master of a ship bound for a US port reports any death or ill person immediately to the nearest CDC quarantine station |
| 42 CFR 71.21(c)[8] | Ships with 13 or more passengers report the gastrointestinal case count 24 hours before arrival, even if zero, and any new case at least 4 hours before |
| 42 CFR 71.1[9] | Acute gastroenteritis counts as an ill person: 3 or more loose stools in 24 hours, or vomiting plus another symptom such as fever of 100.4 F or more |
| VSP thresholds[11] | Special report at 2% of passengers or crew; outbreak declared at 3% |
For the full reporting chain, see vessel illness outbreak reporting and reporting death or illness to CDC.
Hand sanitizer is not enough
CDC says hand sanitizer does not work well against norovirus and is not a substitute for handwashing with soap and water[3]. Clean contaminated surfaces with bleach at 1,000 to 5,000 ppm, which is 5 to 25 tablespoons of household bleach per gallon of water, left on for at least 5 minutes[3].
A six-step norovirus plan for any vessel
- Define a case using the 42 CFR 71.1 wording, so every officer logs the same thing[9].
- Log every case with time of onset and cabin in the medical log; a second case in 24 hours is a signal.
- Isolate and stand down: ill crew stay off food and care duties until at least 48 hours after symptoms stop[3].
- Switch cleaning to bleach at 1,000 to 5,000 ppm and make soap-and-water handwashing the rule at galley and mess[3].
- Report on time: immediately for ill persons on a US-bound voyage, and 24 and 4 hours before arrival on passenger ships[8].
- Watch for dehydration: stock oral rehydration salts and antiemetics in the medicine chest, and treat a crew member who cannot keep fluids down as a medevac question.
Discovery Health MD writes the outbreak protocol and stocks the chest behind it: maritime medical consulting for written procedures and reporting, and ship medical chest management for supplies. Related: ship sanitation certificates and potable water rules. Ask us to review your outbreak plan.
Common questions
How often does norovirus hit cruise ships?
CDC posted 23 gastrointestinal outbreaks in 2025, 18 of them norovirus, and 18 in 2024[5]. Posted outbreaks are only those reaching 3% of passengers or crew[4].
What are the first signs of norovirus?
Diarrhea, vomiting, nausea and stomach pain, usually 12 to 48 hours after exposure; fever, headache and body aches are less common[2].
Does hand sanitizer kill norovirus?
Not well. CDC says to wash hands with soap and water instead[3].
How long is a crew member contagious?
The virus can be in stool before symptoms and for two weeks or more after recovery[3]. CDC advises no food preparation until at least 48 hours after symptoms stop[3].
Do cargo ships have to report norovirus to CDC?
The master of any ship bound for a US port must report ill persons, which includes acute gastroenteritis, to the nearest quarantine station[8][9]. The 24-hour case count applies to ships with 13 or more passengers[8].
What disinfectant kills norovirus on a ship?
Chlorine bleach at 1,000 to 5,000 ppm with at least 5 minutes of contact time[3].
Are crew or passengers more affected?
Passengers, on average: a review of 45 outbreaks found attack rates of 7% in passengers and 2% in crew[12].
