Managing a Gastrointestinal Outbreak on Board
Each AGE case is identified and managed promptly under the applicable plan; in VSP, 2% triggers a special report and 3% or an unusual pattern triggers outbreak/investigation criteria, separately for passengers and crew.
Operational Explanation
The CDC case definition includes three or more loose stools in 24 hours or more than normal, OR vomiting with at least one of diarrhoea, muscle ache, headache, abdominal cramp or fever. Manage and isolate each identified case under the applicable plan without waiting for 3%.
Regulatory Reference
No percentage threshold exists in the International Health Regulations: the percentages belong to two distinct regional regimes, which must be kept apart.
CDC Vessel Sanitation Program (ships with 13 or more passengers calling at US ports, or within 15 days of arrival): an outbreak is defined as an acute gastroenteritis rate of 3% or more of passengers or crew, or an unusual illness pattern or characteristic even below 3% — the second limb of the definition is the one most often forgotten. A special report is due at 2% and again at 3%, in addition to the 24-hour and 4-hour pre-arrival reports.
EU SHIPSAN: the outbreak is defined qualitatively, as an increase in cases above the number normally occurring on that ship. The percentages are only notification thresholds to the port competent authority, at 2% and 3%, and are calculated separately for passengers and for crew, not on the total persons on board.
The International Health Regulations do have an article, and it concerns the certificate. Article 39 of the International Health Regulations 2005 governs Ship Sanitation Control Certificates and Ship Sanitation Control Exemption Certificates: valid for a maximum period of six months, extendable by one month in the cases provided, conforming to the model in Annex 3. If a valid certificate is not produced, or evidence of a public health risk is found on board, the State may proceed under Article 27, paragraph 1: disinfection, decontamination, disinsection or deratting.
But the certificate is not the outbreak. The IHR fixes no percentage threshold for gastroenteritis, and the percentages one meets belong to the two regional regimes already distinguished below. Confusing the Article 39 certificate duty with a national programme's notification threshold is what leads to notifying too late.
Scope of Application
The 2% and 3% thresholds belong to VSP for ships in its jurisdiction and are calculated separately for passengers and crew. Elsewhere apply IHR, SHIPSAN, port-health and ship-plan requirements.
Procedure / How to Complete It
- Apply both limbs of the case definition.
- Manage and isolate each case under the plan without waiting for a threshold.
- For VSP ships, special-report at 2% and treat 3% or an unusual pattern under outbreak/investigation criteria.
- Outside VSP apply competent-authority requirements.
Practical Example
A passenger with vomiting and abdominal cramps meets the AGE definition without three loose stools and is managed immediately. VSP percentages are then calculated separately for passenger and crew populations.
What Typically Goes Wrong
An incomplete definition, waiting for a threshold before managing a case, extending VSP percentages beyond jurisdiction, or presenting dynamic statistics without a date and as causal proof leads to wrong decisions.
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Waiting until the 3% threshold is reached before stepping up cleaning and surveillance, instead of acting already at the 2% reporting threshold | Failure to prevent progression toward a formal outbreak that could have been contained earlier | Step up prevention measures already on reaching the 2% reporting threshold, without waiting for the formal 3% threshold |
| Syndromic surveillance not systematic or based only on spontaneous passenger reports | Underestimation of the actual percentage of symptomatic cases on board, with delayed detection of the threshold | Maintain an active, systematic syndromic surveillance system, not based solely on spontaneous reports |
What the PSCO Checks
Operational Tips
- Act already at the 2% reporting threshold, do not wait for the formal 3% outbreak threshold: the gap between the two thresholds is the operational space to prevent escalation.
- Maintain a systematic syndromic surveillance system, not based solely on spontaneous passenger reports.
- Always document cooperation with health authorities during the epidemiological investigation: it is part of proper outbreak management, not just a subsequent formality.
Preparation checklist
- Both AGE limbs applied
- Case measures started promptly
- 2% and 3% confined to VSP scope
- Passengers/crew calculated separately
- Local requirements checked
FAQ
Related Topics
Last substantive revision of this page: 15 August 2026 · page fingerprint bf52ed50edc8