Every ship that travels to foreign ports, carries 13 or more passengers and calls on a port in the United States is subject to the Vessel Sanitation Program, which is overseen by the Centers for Disease Control and Prevention (CDC). These vessels are inspected (unannounced) twice a year, and subject to re-inspection, when necessary. Currently there are over 140 ships that participate in this program.

Inspections focus on:

• the ship's water supply - to determine how water is stored, distributed, protected, and disinfected.
  
  
• the ship's pools and spas - to ensure proper filtration and disinfection.
  
  
• the ship's food - to determine how is food protected during storage, preparation, and service.
  
  
• the potential for contamination of food and water - to determine what interventions are needed for surveillance.
  
  
• the practices and personal hygiene of the ship's staff - to ensure use of appropriate hygienic practices and cleanliness.
  
  
• the general cleanliness and physical condition of the ship - to ensure cleanliness and the absence of insects and rodents.
  
  
• the ship's training programs in general environmental and public health practices - to determine the scope and effectiveness of this training.

Ships are given a score based on a 100-point scale. To pass inspection, a ship must score 86 or above. If a ship fails inspection, it will generally be re-inspected within 30 to 45 days.

Please see Travel Medicine Additional Online Resources for inspection scores published online, as well as in a publication (often referred to as the "green sheet"), which is distributed to 6,000 travel-related services around the world.

Generally, the lower the score, the lower the level of sanitation. However, a low score does not mean passengers will suffer gastrointestinal or other illnesses. Ships are required to maintain a standardized gastrointestinal illness report for each cruise, with the number of cases of illnesses by dates of onset and total numbers of passengers and crew members affected.

If at least three percent of passengers and/or crew members have gastrointestinal illness on a given cruise, the Vessel Sanitation Program may conduct an investigation to determine if an outbreak has occurred.

Given the number of persons who enjoy cruises each year, the rate of gastrointestinal illnesses on cruise ship is very low. In the 1970s and early 1980s, there were 12 to 15 outbreaks of diarrheal illness each year on cruise ships. Since then the number of outbreaks has steadily decreased. In 1999, only three outbreaks were reported.