In the wake of five incidents of disease at sea, including the deadly Legionnaires' outbreak last summer on the Bermuda-cruising liner Horizon , the Centers for Disease Control has asked the cruise industry to adopt two new measures.

The CDC said cruise ships must regularly clean their hot tubs and warn passengers about the dangers of raw and undercooked foods.

The new guidelines are designed to prevent a recurrence at sea of Legionnaires' and gastrointestinal disease, which both broke out last year on luxury liners. Two people died, one of whom was an elderly Horizon passenger, and at least 880 fell ill in total.

The recommendations, which replace vague suggestions on maintenance of hot tubs and whirlpools, are likely to also change industry standards in hospitals, nursing homes, hotels and health clubs.

The CDC released the guidelines yesterday at its annual meeting with cruise industry representatives in New York City. They were to be effective immediately, and apply to ships with foreign destinations docking in the United States.

The guidelines are not law, and the CDC can't fine or ground ships.

But ships that don't meet the standards could lose money if the CDC publicly announces health hazards or recommends that a cruise be cancelled because of dangerous conditions.

The CDC oversees the federal inspection programme for cruise ships, which carry more than four-and-a-half million passengers a year.

John Estes, president of the International Council of Cruise Lines, said his concern was how the guidelines would be implemented. "In principle, there is no problem,'' he said.

There was an outbreak of Legionnaires' disease, a pneumonia-like illness transmitted by contaminated water, aboard the Celebrity Cruises ship Horizon between April 30 and July 9 during her New York-Bermuda season. One person died and 50 became ill. On CDC orders, Horizon was evacuated in Bermuda and hundreds of passengers were put up at local hotels and flown home the next day, while the ship went out to sea to flush its water systems.

CDC scientists found Legionella bacteria in a contaminated filter that recirculated water for the ship's three whirlpool spas.

The new guidelines for hot tubs include changing filters more frequently, testing water hourly and closing tubs at least four hours a day to increase chlorination.

The old guidelines recommended that crews periodically change hot tub filters, but did not spell out how often.

The four outbreaks of gastrointestinal disease last year on another liner which did not cruise to Bermuda are believed to have originated in raw or undercooked food. At least 830 people were sickened and one man was killed.

The CDC also recommends that cruise ship operators warn passengers about the possible risks of eating raw or undercooked food.

The CDC plans to increase by about 28 percent the inspection fees that ships pay the CDC. Fees are based on the ship's tonnage and currently range from about $3,100 to more than $6,300.

CDC inspectors check ships twice a year on 42 items related to water, food preparation, food storage and cleanliness. Last year, the programme's four officers conducted 188 inspections.