Gastrointestinal Illness Surveillance and Outbreak Investigations
Syndromic Surveillance of Gastrointestinal Illnesses
The Vessel Sanitation Program (VSP) maintains an electronic surveillance system that tracks cases of gastrointestinal illnesses. We use this system to help the cruise ship industry prevent and reduce gastrointestinal illnesses on cruise ships. We monitor the system to observe illness patterns.
How does the surveillance system work?
Cruise ship medical staff or other designated personnel are required to maintain a log of reported cases of gastrointestinal illnesses.
Passengers and crew tell ship medical staff they are sick.
If it is a gastrointestinal illness, it is entered in the log.
Medical staff send a report to VSP that shows the total number of gastrointestinal illness cases for both passengers and crew.
When are gastrointestinal illnesses reported to VSP?
Cruise ship medical staff are required to send gastrointestinal illness case reports to VSP at the following designated times:
- Before arriving to a U.S. port from a foreign port. This report is required even when there are no cases of gastrointestinal illness. This report is made 24–36 hours before arriving to the United States.
- If the number of ill passengers or crew changes after the initial notification in the bullet above, but before the ship is 4 hours from arrival.
- When 2% or more of the passengers or crew are ill with gastrointestinal illness. This report must be sent at any time the vessel is in the United States or within 15 days of arriving to a U.S. port.
- When unusual gastrointestinal illness symptoms are reported to the ship’s medical staff.
What does VSP do with the reports?
We monitor reports of gastrointestinal illness to
- Determine if a high number of people are sick.
- Determine if unusual cases occur.
- Provide support to the cruise line and cruise ship crew as they respond to an increase in cases.
- Analyze illness patterns over time.
Cruise lines are required to develop an Outbreak Prevention and Response Plan (OPRP). The OPRP must
- Indicate trigger points that initiate a ship’s response to cases of illness.
- Identify overall outbreak management strategies.
- Include detailed infection control procedures for each area of the ship.
What does VSP do when an outbreak occurs?
When an outbreak occurs, we ask for logs and records, including gastrointestinal illness surveillance logs, so we can closely examine the reported cases. The surveillance logs include information such as specific symptoms and the date and time the illness occurred. By reviewing the logs, we are able to determine the following:
- Amount of illness throughout the ship.
- Distribution of illness among the passengers and crew.
- When the illness first began.
- Distribution of illness during each day of the voyage.
- Profiles of the ill people’s symptoms.
When does VSP conduct an outbreak investigation?
VSP conducts outbreak investigations on ships sailing in the United States or within 15 days of arriving to a U.S. port. These ships must also have one of the following:
- 3% or more of the passengers or crew reporting they are sick with symptoms of gastrointestinal illness.
- Report of illness symptom(s) or occurrence(s).
- An outbreak the ship has difficulty getting under control.
Where are outbreak investigations conducted?
Outbreak investigations may be conducted either in the office or on a cruise ship.
When CDC conducts an investigation in the office, we
- Evaluate ship records, including gastrointestinal illness surveillance logs;
- Establish daily contact with cruise line officials to determine if proper sanitation practices are being applied;
- Assess current outbreak management practices; and
- Make recommendations for outbreak management.
Cruise ship staff collect clinical specimens, such as stool samples, or environmental specimens, such as water samples. They send these samples to a land-based laboratory to test for cause(s) of the outbreak.
When CDC conducts an investigation on-site, we first follow the same steps as in an office investigation.
CDC staff also board the cruise ship to do one or more of the following:
- Epidemiological assessment to examine the distribution of gastrointestinal illnesses, interview passengers and crew members, and distribute and analyze questionnaires.
- Targeted environmental health assessment to investigate specific areas on the vessel to check for exposure and routes of transmission of the illness and to monitor the ship’s OPRP procedures. This assessment is based on preliminary findings from the epidemiological review.
What does VSP require cruise lines to do during outbreaks?
Cruise lines are required to activate their Outbreak Prevention and Response Plan (noted above under the Preventing Outbreaks section) and make every effort to gain control of the outbreak. Control measures include the following:
- Increase daily cleaning and disinfection frequencies.
- Stop high-risk activities, such as self-service buffet tables and handshaking.
- Isolate ill people.
- Collect clinical and/or environmental specimens for analysis.
- Provide daily updates to VSP that include case counts and reports of what the ship has done to establish control.
- Alert passengers and staff of the illness.
- Provide information about proper handwashing.
- Notify new passengers about the outbreak before embarkation.
VSP may also ask cruise lines to do the following:
- Notify port authorities.
- Delay embarkation of the next voyage.
- Establish cleaning and disinfection procedures in terminal buildings.
Where can I find information about a specific outbreak?
We post all outbreak summaries on our website.
What about norovirus?
Norovirus is a very contagious viral illness that makes an estimated 21 million people sick every year in the United States. You can get it from someone who is infected, by eating or drinking contaminated food or water, or by touching something that is contaminated. Norovirus causes inflammation in your stomach or intestines, which may cause you to feel nauseated, have diarrhea, or throw up. To read more about norovirus, visit CDC’s norovirus page.
How do I protect myself from norovirus?
- Use proper handwashing techniques throughout your voyage, but especially after using the bathroom and before eating.
- Avoid any food or water that you think may be contaminated.
- Avoid raw or undercooked shellfish.
- Avoid unnecessary direct hand contact with surfaces such as public toilet room door handles.
- Avoid unnecessary close contact with ill persons.
- See our cruising tips.