Since 1970, CDC’s Vessel Sanitation Program has maintained a surveillance and reporting system for
cruise ships that have both a U.S. and foreign itinerary and carry 13 or more passengers. The system was
designed to minimize the introduction, transmission, or spread of gastrointestinal illnesses into the
United States. This reporting system, along with other Vessel Sanitation Program components have reduced
and controlled the number of passengers and crew members aboard cruise ships with gastrointestinal
The cruise industry is rapidly growing and now serves more travelers and has more extensive
itineraries than ever before. Because of the increases in itineraries and the number of passengers on
cruise ships, itineraries and the number of passengers on cruise ships, more people are at risk for GI
illnesses while traveling. Cruise ship passengers and crews are also at risk for new patterns of old
diseases or newly recognized causes of diseases. VSP protects passenger and crew health by minimizing the
risk of gastrointestinal illness aboard cruise ships.
What are cruise ships required to do?
Cruise ships are required to log and report the number of passengers and crew members that have
reported having symptoms of gastrointesintal illness. Additionally, vessels are required to keep a list of all
passengers and crew members that have requested antidiarrheal medication.
What does VSP look for when monitoring gastrointestinal illness reports?
VSP provides assistance to cruise ships when the number of ill passengers or crew members has reached
2% or more of the total number of passengers or crew members or when an unusual GI pattern or
characteristic is found. VSP monitors and evaluates GI illnesses aboard ships to determine the cause of
the outbreaks and to make recommendations for control. To accomplish this, VSP officials do the following:
1. Review the magnitude of gastrointestinal illnesses among passengers and crew.
2. Monitor distribution of gastrointestinal illnesses among both passengers and crew members.
3. Assist in the assessment of changes in sanitation practices, in infectious agents, and in types of
4. Evaluate the effectiveness of prevention and control strategies.
5. Provide lab support to confirm the cause of the illness.
A reportable case of GI illness is three or more loose stools within a 24-hour time period, or
vomiting along with one of the following symptoms: muscle ache, headache, abdominal cramp, or fever.
What are unusual GI illness patterns or characteristics?
Examples of unusual GI illness pattern or characteristic are relatively high incidences of illnesses
in successive cruises, unusual severity of illnesses or complications, high numbers of persons reporting
illnesses over a brief period, or suspicion of an uncommon causative agent.
When does CDC conduct an investigation?
VSP and other CDC officials may conduct an investigation if at least 3.0% of the ship’s passengers or
crew members have GI illness, or if an unusual gastrointestinal illness pattern or characteristic is found
(even if the illness rate is less than 3%).
What happens during an onboard investigation?
During an onboard investigation, CDC officials work with cruise ship staff to determine the cause of
The objectives of an investigation are to:
1. Determine the magnitude of illness aboard the ship.
2. Identify the agent causing the illness.
3. Identify risk factors associated with the illness.
4. Formulate control measures to prevent or stop the spread of illness.
By determining the cause of an outbreak, CDC officials can help devise effective intervention
strategies to prevent a recurrence of the outbreak.
The investigation has three parts:
1. Epidemiological investigation: The incidence and distribution of the GI illness is evaluated on the
basis of passenger and crew member activity questionnaires, general cruise ship layout, menus, medical
records, and other pertinent data.
2. Laboratory investigation: Medical staff may collect stool, blood, or vomit specimens to send to a
land-based lab to confirm the cause of illness.
3. Environmental health investigation: An environmental health investigation is based on the preliminary
findings of the epidemiological investigation. For example, if water is suspected to be the source of the
illness, more attention will be spent reviewing the water source.
What happens to the information collected during an investigation?
When possible, VSP officials present a preliminary report of findings and recommendations to the
master of the ship before leaving the ship.
When the investigation is complete, a final report is sent to the cruise line results on of the
epidemiological, laboratory, and environmental analyses. Summary recommendations for control and
prevention are also included in the report.
How is this information made available to the passengers?
Passengers can find a copy of the report on this website, emailing
CDCINFO@cdc.gov, or by writing: