A study suggests one possible culprit: dirty restrooms. Most restrooms on these ships are not being properly cleaned, the authors say, and a sanitation program run by the Centers for Disease Control and Prevention does not detect the dirty ones.
According to researchers writing in the Nov. 1 issue of Clinical Infectious Diseases, the C.D.C. identified contamination with norovirus as the problem in almost all of these infections. But the ships generally had high passing scores on the inspection closest to their outbreaks. In fact, their scores were on average higher than those of ships with passengers who had no episodes of diarrheal disease.
Norovirus can survive for weeks on surfaces at room temperature, and it is difficult to kill. “It’s a tough virus,” said the lead author of the study, Dr. Philip C. Carling. “It isn’t killed by alcohol hand rubs. Chlorine bleach is the only thing that works.”
There were 19 outbreaks of intestinal illness during the 3-year study period. Although 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 difference was not statistically significant, but the authors said the findings were consistent with the possibility that restroom contamination contributed to norovirus epidemics.
“We’re not saying that poor cleaning causes norovirus outbreaks,” Dr. Carling said, adding, “I believe that one or more people with norovirus who handle food, or possibly a passenger, comes down with norovirus, and substandard hygiene serves as a facilitator of the spread in a closed population.”