Norovirus is a word that every cruise ship vacationer fears.  Now a new study suggests that dirty public bathrooms on cruise ships may play a role in encouraging dreaded cruise ship norovirus outbreaks.

Norovirus, which can survive for weeks on surfaces at room temperature,  can be difficult to eliminate, and can only be killed with chorine bleach. Alcohol-based hand sanitizers and other preparations are not too helpful. Norovirus outbreaks  occur frequently in closed populations, such as cruise ship passengers  According to The New York Times,  there have been more than 60 outbreaks of norovirus on cruise ships since 2005.

This latest study, which appears in the Nov. 1 issue of  “Clinical Infectious Diseases”,  used trained health care professionals  to covertly evaluate the “Thoroughness of Disinfection Cleaning” of 6 standardized objects (toilet seat, flush handle or button, toilet stall inner handhold, stall inner door handle, restroom inner door handle, and baby changing table surfaces) with high potential for fecal contamination in cruise ship public restrooms.  To do this, the investigators used an easily removable solution visible only under ultraviolet light to mark the objects. Then they monitored them for five to seven days to see if the solution had been removed by cleaning or disinfecting.

Over the course of the study, the investigative team evaluated 56 cruise ships (less than 30 percent of the vessels operated by 9 large cruise lines)  from July 2005 through August 2008. There were 19 outbreaks of intestinal illness during the 3-year study period. While the survey was not designed to detect norovirus or establish the cause of any illness, the restroom cleanliness scores were slightly lower on ships that had outbreaks than on those that had none. The investigators found that  37 percent of 8,344 objects in 273 randomly selected cruise ship public restrooms were cleaned daily.

The investigation also  found that the U.S.  Centers for Disease Control and Prevention (CDC), which runs a cruise ship sanitation program, is not doing a very good job of detecting the dirty cruise ship bathrooms. According to the study,  more than half the cruise ships had overall “Thoroughness of Disinfection Cleaning” scores under 30 percent, although several of these low-scoring ships had near-perfect CDC sanitation scores. The mean “Thoroughness of Disinfection Cleaning” score of the three ships evaluated within four months of an norovirus outbreak (10.3%) was substantially less than the mean “Thoroughness of Disinfection Cleaning” score  of the 40 ships that did not experience such an outbreak (40.4).