VSP Outbreak Investigations

Learn what we do during investigations of gastrointestinal illness outbreaks on cruise ships.

The Vessel Sanitation Program (VSP) monitors our surveillance system to observe illness patterns for gastrointestinal illness on cruise ships.

VSP conducts outbreak investigations when 3% or more of the ship’s passengers or crew members report they are sick with symptoms of gastrointestinal illness. We may also conduct an outbreak investigation if an unusual gastrointestinal illness pattern or characteristic is found (even if the illness rate is less than 3%).

We conduct outbreak investigations on ships sailing in the United States or within 15 days of arriving at a U.S. port.

Investigators seated at a table discussing findings

What does VSP do in an outbreak investigation?

During an outbreak investigation, VSP works with cruise ship staff and the cruise line to determine the cause of illness.

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 can determine the following:

  • How many passengers and crew are sick on the ship.
  • When illness started and how long it lasted.
  • How many people are sick on each day of the voyage.
  • Symptoms of people who are sick.

The objectives of an investigation are to

  • Determine the magnitude of illness aboard the ship.
  • Identify the pathogen causing the illness.
  • Identify risk factors associated with the illness.
  • Formulate control measures to prevent or stop the spread of illness.

By determining the cause of an outbreak, VSP can help the cruise line develop effective intervention strategies to prevent a recurrence of the outbreak.

During an outbreak, VSP staff may board a cruise ship to do one or more of the following:

  • Epidemiologic assessment to look at the spread or pattern of gastrointestinal illness, interview passengers and crew members, and analyze questionnaires with details on recent crew and passenger activities.
  • Targeted environmental health assessment to investigate specific areas to check for exposure and routes of illness transmission and to monitor the ship’s outbreak prevention and response plan procedures. Targeted environmental health assessments are based on preliminary findings from the epidemiologic assessment. For example, if water is suspected as the source of illness, VSP gives more attention to reviewing places on and off the ship where people could have been exposed to contaminated water.
  • Laboratory investigation to confirm the cause of illness. Medical staff may collect stool, vomit, or blood specimens to send to a land-based laboratory.

What does VSP require cruise lines to do during outbreaks?

Cruise lines are required to activate their outbreak prevention and response plans and make every effort to gain control of the outbreak. These plans

  • 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.

Cruise line control measures include the following:

  • Increasing daily cleaning and disinfection frequencies.
  • Stopping high-risk activities, such as self-service buffets and handshaking.
  • Isolating ill people.
  • Collecting clinical and/or environmental specimens for analysis.
  • Providing daily updates to VSP that include case counts and reports of what the ship has done to establish control.
  • Alerting passengers and crew of the illnesses onboard.
  • Providing information about proper handwashing.
  • Notifying new passengers about the outbreak before they get on the ship.

VSP may also ask cruise lines to

  • Notify port authorities.
  • Delay bringing passengers on board for 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.

How can I protect myself from gastrointestinal illness?

  • 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 tips for healthy cruising.