Gastrointestinal Illness Surveillance and Outbreak Investigations
Syndromic Surveillance of Gastrointestinal Illnesses
To assist the cruise ship industry to prevent and reduce gastrointestinal illnesses on cruise ships, CDC maintains an electronic surveillance system that tracks cases of gastrointestinal illnesses. 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. Cases are self-reported by passengers and crew. Medical staff send a report to VSP that indicates the number of cases.
When are gastrointestinal illnesses reported to VSP?
Cruise ship staff are required to send GI illness case reports to VSP during 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. It is made 24–36 hours before arriving to the United States;
- if the case count of ill passengers or crew changes after making the initial notification in the bullet above;
- 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; and
- when unusual 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; and
- analyze illness patterns over time.
Prior to the occurrence of an outbreak, 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. It must identify overall outbreak management strategies and include detailed infection control procedures for each area of the vessel.
What does VSP do when an outbreak occurs?
When an outbreak occurs, we request logs and records, including gastrointestinal illness surveillance logs, so that we can closely examine the reported cases. The surveillance logs include information such as specific symptoms and the date and time that 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; and
- symptom profiles.
When does VSP conduct an outbreak investigation?
VSP conducts outbreak investigations on ships that are sailing in the United States or are within 15 days of arriving to a U.S. port and when one of the following is true:
- 3% or more of the passengers or crew have reported being sick with symptoms of gastrointestinal illness; or
- an unusual illness symptom(s) or occurrence(s) is reported; or
- an outbreak has occurred, and the ship has difficulty in getting the outbreak under control.
Where are outbreak investigations conducted?
Outbreak investigations may be conducted either in the office or on a cruise ship. The following describes what occurs during each investigation
- In the office: CDC staff 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, and send them to a land-based laboratory to test for possible cause(s) of the outbreak.
- On-site investigations: In addition to the in-office investigation listed above, CDC staff board the cruise ship to do one or more of the following:
- epidemiological assessment: examine the distribution of gastrointestinal illnesses, interview passengers and crew members, and distribute and analyze questionnaires;
- targeted environmental health assessment: based on preliminary findings from the epidemiological review, investigate specific areas on the vessel to check for exposure and routes of transmission of the illness; and
- laboratory assessment: cruise ship staff collect clinical specimens, such as stool samples, or environmental specimens, such as food, and send them to a land-based laboratory to test for the possible cause(s) of the outbreak.
What does VSP require cruise lines to do during outbreaks?
Cruise lines are required to activate their Outbreak Prevention and Response Plan (mentioned above under Preventing Outbreaks) and make every effort to gain control of the outbreak. Some control measures include:
- 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; and
- provide daily updates to VSP that include case counts and reports of what the ship has done to establish control.
Additionally, VSP may request cruise lines to do the following:
- alert passengers and staff of the illness;
- provide information about proper handwashing;
- notify new passengers about the outbreak prior to embarkation;
- notify port authorities; and
- establish cleaning and disinfection procedures in ports.
Where can I find information about a specific outbreak?
We post all outbreak summaries on our Web site.
What about norovirus?
An increase in the number of norovirus outbreaks in 2006 and 2007 in the United States occurred at the same time as the appearance of two new types of norovirus, called GII.4 Minerva and GII.4 Laurens, respectively. These types of norovirus caused 79% of the outbreaks, but it's not clear if the increase in outbreaks is directly related to how these new types of norovirus were spread, to their ability to cause illness, or to another unknown factor.
(Centers for Disease Control and Prevention. Norovirus Activity --- United States, 2006--2007, Morbidity and Mortality Weekly Report August 24, 2007; 56; 842-846)
How do I protect myself from norovirus?
- engage in 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, unnecessary direct hand contact with surfaces such as toilet room door handles, and unnecessary close contact with symptomatic ill persons; and
- see our cruising tips.