NEW YORK - Going on a cruise? To cut your risk of getting sick while sailing the high seas, avoid using the ship's public bathrooms.

Researchers have found that only 37 percent of 273 randomly selected public restrooms on cruise ships that were checked on 1,546 occasions were cleaned at least daily, with the toilet seat the best cleaned of six evaluated objects.

On 275 occasions no objects in a restroom were cleaned for at least 24 hours with baby changing tables found to be the least thoroughly cleaned object.

Researcher Philip Carling, of Carney Hospital in Boston, Massachusetts, said public toilet seats and flush devices,
stall handholds and door handles, inner restroom door handles, and baby changing tables "on most, but not all, cruise ships" are not being cleaned and disinfected thoroughly.

"There was a substantial potential for washed hands to become contaminated while the passenger was exiting the
restroom, given that only 35 percent of restroom exit knobs or pulls were cleaned daily," Carling said in a statement.

"Only disinfection cleaning by cruise ship staff can reasonably be expected to mitigate these risks."

Lack of disinfection, he and colleagues from the Cambridge Health Alliance and Tufts University School of Medicine, noted in the journal Clinical Infectious Diseases, may significantly increase risk for illness, and particularly for the severe diarrhoea and vomiting caused by highly contagious norovirus.

Carling told Reuters Health that cruise passengers should minimize public restroom use, wash hands with soap and water rather than alcohol-based hand rubs, and be aware of the disease transmission potential from all publicly touched surfaces.

For the study, Carling's group enlisted 46 health professionals to check 273 randomly selected public restrooms daily during cruises between July 2005 and August 2008.

The ships most originated from U.S. ports and 82 percent from the five largest cruise lines.

Armed with handheld ultraviolet lights to pick up florescent traces of a transparent, but easily cleanable solution they had previously sprayed on surfaces, the cleaning spies identified surfaces left uncleaned for 24 hours.

Toilet seats were the best-cleaned object. Of the 2,010 toilet seats evaluated, 50 percent had been cleaned. They found 42 percent of toilet flush devices, 37 percent of toilet stall doors, and 31 percent of stall handhold bars had been cleaned.

Only 35 percent of interior bathroom door handles and 29 percent of baby changing tables had been cleaned.

Post-outbreak cleaning and disinfection practices on cruise ships, although important, are not enough, the researchers say.

Increased efforts to prevent outbreaks with better disinfection practices are clearly needed.