The medical journal "Clinical Infectious Diseases" published an article entitled "Disease Transmission and Passenger Behaviors During a High Morbidity Norovirus Outbreak on a Cruise Ship, January 2009."
Of some 1842 passengers on the cruise ship, 1532 (83%) returned questionnaires provided by the researchers. 236 (15%) met the norovirus definition.
This particular cruise had a passenger vomit in a public area during boarding, as well as 7 other incidents where passengers vomited in public. The Centers for Disease Control ("CDC") investigators concluded that some sick passengers may have been infected by the vomit (through aerosolized vomit or by touching contaminated surfaces) or they were infected by person-to-person contact, particularly by an ill cabin mate.
The CDC investigators also concluded that some of the public toilets on the cruise ship were out of hand soap and paper towels and dish washing machines did not do an adequate job sanitizing eating utensils. These shortcomings might have contributed to the outbreak.
Nothing new with these conclusions.
The two interesting points in my opinion revealed in the study:
Of the 236 ill passengers, 95 (40%) did not report to the infirmary. We have been told by many passengers on cruises plagued by norovirus that the actual number of sick passengers reported by the cruise lines to the CDC was far less than the actual number of passengers with norovirus. Cruise lines report only the number of passengers who report to the ship infirmary. This is a problem we have discussed before – Is Celebrity Cruises Under-Reporting Sicknesses to the CDC?
Perhaps the most interesting statistic is that 62% of ill passengers did not decrease their participation in public activities. Over 200 passengers ill with norovirus walking around the ship? Yuck. This undoubtedly led to the spread of the outbreak.
But most outbreaks of norovirus on cruise ships are no so clear cut. There appears to be no effort to scientifically determine the source of norovirus outbreaks.
As we have reported in prior blogs, the U.S. Food and Drug Administration (FDA) concludes that whereas "person to person" transmission of norovirus has been documented, "norwalk gastroenteritis is transmitted by the fecal-oral route via contaminated water and foods." The FDA reports that "water is the most common source of outbreaks and may include . . . water stored aboard cruise ships."
When will the CDC conduct a recent study analyzing the potable water and food products after an outbreak? Compare this study with a study by the CDC in 2002 which the CDC "suspected that initial infection among passengers on cruise 1 originated from a common food or water source and then continued to spread from person to person" and "we identified that eating breakfast at restaurant A on day 2 of the cruise was associated with illness . . ." Or consider "Characterization of a variant strain of Norwalk virus from a food-borne outbreak of gastroenteritis on a cruise ship in Hawaii" (pin-pointing fruit at a buffet as the likely culprit).
Read some of our other articles about cruise ship norovirus:
March 24, 2011 Update: USA Today’s CruiseLog has a story today about this study, indicating that the study involved Celebrity Cruises’ Mercury cruise ship in January 2009. As we pointed out in an earlier blog, the CDC investigated outbreaks on the Celebrity Mercury in January and February 2009.
The interesting thing about the Mercury was that it experienced four cruises a year later, in 2010, with repeated outbreaks of norovirus until the CDC took the unprecedented step of issuing a no sail order, an event we covered last March: Centers for Disease Control: "Shut Mercury Cruise Ship Down!" It would have been interesting for the CDC to have studied the cause of the norovirus on this cruise ship for months in early 2010. Why did this particular cruise ship experience so many problems with norovirus? Certainly it was not just because a passenger puked on embarkation in January 2009?