Is "New" Norovirus to Blame for Cruise Ship Outbreaks?

April 20, 2007
Earlier this month, 26 passengers and 7 crewmembers fell ill with Norovirus on Majestic America Line's Empress of the North; late last year, Royal Caribbean's Freedom of the Seas and Carnival's Carnival Liberty were taken out of service for extensive cleaning after instances of the gastrointestinal illness. Cruise ship outbreaks are on the rise -- is a hearty new strain of Norovirus to blame?

Well, partly. Dr. Jan Vinje, the head of the Centers for Disease Control and Prevention's gastroenteritis and respiratory viruses lab, tells us that between October and December of 2006, roughly 60 percent of all Norovirus cases were traced to the new strain, which is being called Minerva -- with the other 40 percent or so linked to various other strains. Those percentages, he says, are pretty much the same on land and at sea, since in most if not all cases, the virus is spread when an already-ill passenger boards a ship and spreads it around.

However, the good news is that while there has been an increase of Norovirus outbreaks on ships, it's not a huge one: In 2005, Dr. Vinje tells us, there were 23 confirmed Norovirus outbreaks; in 2006, that number went up just slightly, to 26. So far this year, a dozen outbreaks of gastrointestinal illness have been investigated by the CDC, according to the Vessel Sanitation Program's Web site (Norovirus has been confirmed as the cause in only five cases).

Indeed, despite the fact that Norovirus has a bad rap as a "cruise ship" virus (it's not; we dispel that myth here), the new strain is wreaking more havoc on land, in nursing homes and hospitals for example, than on vessels at this point. According to Dr. Vinje, Minerva has hit the West Coast and Northeast very hard. This new strain is stronger, longer lasting and more contagious -- and in these regions, outbreaks have been lengthy and the clinical symptoms have been quite severe. Meanwhile, the outbreaks on cruise ships have not significantly changed in terms of severity.

At this point in time, Dr. Vinje says that cruise ships are using the same disinfectants (the CDC maintains a list of recommended products) and protocols to treat all strains of Norovirus. Additional help might be on the way: Pennsylvania-based PuriCore, a life sciences company, offers disinfecting systems designed to limit the spread of infections diseases like E. coli, avian influenza -- and Norovirus.

The company received FDA approval earlier this month to market the system, Sterilox, in the U.S as a medical device, but industry sources tell us that Sterilox can also be used to eliminate -- and prevent -- Norovirus on cruise ships. There are different versions of the product, from topical applications to disinfecting fogging machines; we heard about one precautionary measure in particular that would work in a different way than the surface wipes traditionally used on vessels. A Sterilox solution would be applied to a countertop, for example, and actually prevent Norovirus from growing there for a month or more at a time.

A spokesman for PuriCore did not know when and if particular products will find their way into the hospitality industry and specifically onboard cruise ships, but that Sterilox could certainly be used to sanitize passenger vessels.

"We are doing all kinds of studies and looking at different disinfectants," Dr. Vinje says. "We cannot really assess the effectiveness of these disinfectants [because] we cannot grow those Noroviruses in a lab. The only way to find out if you can really kill the virus is to be able to grow the virus. What we have been doing is looking for surrogate viruses that are almost identical. We have been working with a mouse Norovirus."

Norovirus is not a "cruise ship" virus, nor does it limit itself to sea-going vessels; Norovirus is the second most prevalent illness in the U.S. after the common cold and the CDC estimates that there are 23 million cases annually. Cruise ship cases make the news because lines are required to notify the CDC when 3 percent or more of passengers or crew report symptoms -- not the case for land-based facilities like hotels and hospitals.

The Minerva strain began popping up in 2005 but became a real problem toward the end of 2006; like the flu, a newly emerged strain often causes the most damage during the next major "season." Minerva's been found in Asia, Australia and Europe as well as North America.

Want to know more about Norovirus, and how you can stay healthy at sea? Read Norovirus: What You Need to Know.

--by Melissa Baldwin, Senior Editor