New Study Aims to Link Dirty Cruise Ship Restrooms to Norovirus

November 3, 2009
(6 p.m. EST) -- You can wash your hands all you like -- but if the public restrooms on cruise ships haven't been cleaned properly, could Norovirus be your least-wanted holiday souvenir?

According to a team of researchers from Boston University School of Medicine, Carney Hospital, Cambridge Health Alliance and Tufts University School of Medicine, there could be a link between a lack of thorough cleaning of public restrooms on cruise ships and subsequent outbreaks of acute gastroenteritis. Some 95 percent of these cruise ship outbreaks, the report states, are caused by Norovirus (NoV).

The research has just been published in the the Infectious Diseases Society of America (IDSA) journal, "Clinical Infectious Diseases," and is hailed as the first study of its kind on cruise ships.

But wait a minute. Isn't this stating the obvious? We've all been bombarded with the hand sanitizers, "wash your hands" messages and gastroenteritis disclosure forms on boarding. Don't we already know the formula? Poor hygiene plus people living in close environment equals likelihood of illness spreading?

The reality is more subtle. The undercover researchers, all of whom had health care training, evaluated the "thoroughness of disinfection cleaning" (TDC) of 56 large ships belonging to nine cruise lines between July 2005 and August 2008. There's no naming and shaming of ships, but there are two interesting findings.

First, the results didn't necessarily match those of the United States' Centers for Disease Control (CDC) and Prevention Vessel Sanitation Program. (All vessels carrying more than 13 passengers and entering a U.S. port from a foreign port are subject to surprise CDC inspections. A similar scheme exists in the U.K.) CDC scores averaged 97 out of a possible 100 points for the 56 study vessels, according to the survey, while the researchers' own scores were much lower on many of the vessels -- keeping in mind, of course, that the CDC scores a ship on many facets of food safety and surface cleanliness, while this study focused only on restrooms.

Second, this particular study contends that ships with less clean restrooms are more likely to have a Norovirus outbreak. Three of the ships were evaluated within four months of a Norovirus outbreak (confirmed by the CDC and affecting two percent or more of passengers and crew). Though it's unclear whether illness was an issue before or after the evaluations, the mean TDC on these ships was 10.3 percent -- substantially less than the mean TDC of the 40 ships that did not experience any Norovirus, which was 40.4 percent.

Statistics aside, it's not the fact that restrooms are cleaned that matters -- all restrooms on cruise ships are cleaned -- but which items in these restrooms are cleaned, and how often.

The researchers monitored six objects: toilet seat, flush handle or button, toilet stall inner handhold, stall inner door handle, restroom inner door handle, and baby changing table surfaces, all of which have with high potential for fecal contamination in cruise ship public restrooms.

The researchers found that only 37 percent of the 273 randomly selected public restrooms that were evaluated on 1,546 occasions were cleaned daily. The overall cleanliness of the six surfaces on each ship ranged from a worrying 4 percent to a more impressive 100 percent. Although some objects in most restrooms were cleaned at least once a day, on 275 occasions, no objects in a restroom were cleaned for at least 24 hours.

Overall, the toilet seat was the best-cleaned object, while the least thoroughly cleaned object was the baby changing table. Some 19 objects on 13 ships were not cleaned at all during the entire five- to seven-day monitoring period.

Toilet area handholds were largely neglected, accounting for more than half of the uncleaned objects on 11 ships. The baby changing table statistics are pretty gross, too; although not all the restrooms had changing tables, on the three ships that did, none of the changing tables were cleaned at all during the study period.

Just as worrying is the door handle. Only 35 percent of restroom exit knobs studied were cleaned daily -- so you could easily pick up Norovirus on leaving the bathroom, just by opening the door. Some lines already recognise this risk; Holland America Line, for one, has posted signs in its public bathrooms advising users to use a tissue or towel when opening the door.

It's not all bad news, though. Although the thoroughness of disinfection cleaning was a miserable 30 percent on more than half of the ships, near-perfect cleaning was documented on several vessels, providing evidence that it is possible to have a spotless bathroom.

"We believe that additional studies on the role of contaminated surfaces in cruise ship NoV transmission are warranted to determine whether improved environmental hygiene will decrease the incidence, duration, or severity of outbreaks," said lead author Philip Carling, MD, a professor of clinical medicine at BUSM, in a press statement.

Cruise Lines International Association (CLIA), which represents 24 major cruise lines, responded via an e-mailed statement: "The cruising industry takes the sanitation of its vessels and the mitigation of all gastrointestinal illnesses, including Norovirus, very seriously. Our comprehensive public health and sanitation procedures -- which go above and beyond ISDA's focus on the disinfecting of public restrooms -- are highly effective in maintaining healthy settings for families on vacation ... the limitations of this research raise appropriate questions that must be answered before a more complete assessment is reached.

"It is worth highlighting that the IDSA study was not designed to investigate the causal relationship -- and did not find one -- between the thoroughness of disinfecting restrooms and outbreaks aboard cruise ships."

Indeed, the fact that a less-than-sparkling loo and Norovirus were found on the same ship does not necessarily mean one caused the other. And, let's face it: There are some pretty dubious public restrooms all over -- in hotels, on planes, at airports, even in nice restaurants. Still, will you avoid the public restrooms onboard and use the bathroom in your cabin in light of these findings? Tell us!

--by Sue Bryant, Cruise Critic Contributing Editor