Christine Duffy, the CEO of the cruise industry trade group Cruise Line International Association (CLIA), has authored an article entitled "CDC report debunks norovirus cruise myth."
The article was first issued as a press release and later picked up by cruise cheerleaders like Cruise Critic. Travel Weekly is the latest travel publication to publish the misleading article.
Ms. Duffy fabricates and distorts information in her article.
She compares norovirus outbreaks on cruise ships with norovirus outbreaks on land. But her method of doing so is inherently flawed and misleading.
She says that In 2013, a little over 10 million people embarked on a cruise from a U.S. port. She claims that there were only 4 norovirus outbreaks, involving around 834 passengers, in 2013. That turns out to be approximately 1 in 12,000 cruise passengers who are affected by the nasty bug, she concludes.
Meanwhile, the CDC estimates that norovirus affected 20,000,000 ashore. With a population of some 318,000.000 U.S. citizens, that turns out to be 1 in 15 people who contract norovirus on land every year.
However, to make a meaningful comparison, you have to compare the U.S. population with the average population of the cruise industry at any given point. There are around 250,000 people cruising at any given time world wide from the major CLIA lines, with around 125,000 sailing from U.S. ports. You don't compare the U.S. population to the total number of travelers. That's like comparing apples to oranges.
A typical cruiser may spend anywhere from 3 days to a week or perhaps 2 or 3 weeks a year cruising. They are not on the cruise ship 52 weeks a year obviously. So it is highly misleading to compare the U.S. population with the total numbers of travelers. It skews the number from 125,000 to over 10,000,000. It understates the likelihood of contracting norovirus on a cruise ship by a factor of 80 or so.
In addition to the flawed methodology, Ms. Duffy's numbers regarding the incidents of cruise norovirus cases are flat-out wrong. She says there were only 4 outbreaks affecting only 834 passenger in 2013.
But the CDC data shows that there are in fact thousands of passengers who are sickened on cruises every year. From February 25, 2013 to February 22, 2014, for example, the CDC reported that there 13 outbreaks totaling 2,468 passengers. So to make a correct statistical comparison, the land-based outbreaks must be compared to 2,468 incidents in a total cruise population of 125,000 (not 834 incidents out of over 10,000,000 people).
Remember that the CDC data is limited. It doesn't include outbreaks when the cruise ship doesn't return to a U.S. port. Even when a U.S. port is involved, it doesn't even record incidents when less than 3% of the total number of passengers become sick. So that means that 175 passengers could become ill with norovirus on the Oasis of the Seas and the CDC would ignore it. The CDC data reveals only a fraction of the actual number of cruise norovirus victims. Plus it's well known in the cruise industry that many passengers don't report their sicknesses to the ship infirmary because they don't want to be quarantined.
During many of the Congressional hearings on cruise ship crimes over the last few years, the cruise industry offered similarly misleading comparative data. It would provide crime statistics using the total U.S. population compared to the total number of passengers who travel on cruise ships. This skewed the statistics wildly in favor of the cruise industry. It made it appear that fewer crimes occur on cruise ships. Congress chastised the industry for providing such misleading comparisons.
Senator Rockefeller criticized Ms. Duffy for not being truthful when she testified before a Senate subcommittee on cruise ship safety in 2012.
It's a shame that travel publications like Travel Weekly publish such rubbish. It's a disservice to the U.S. public who deserve honest numbers and meaningful analysis.