CDC calls cruise ships safe, says shipboard illnesses may be declining

Robert Roos

Dec 3, 2002 (CIDRAP News) Ð Despite several recentoutbreaks of intestinal illness on cruise ships, federal health officials sayit is safe to go on cruises and that the number of illnesses relative to thenumber of passengers may actually be lower this year than in past years.

Dave Forney, chief of the Centers for Disease Control andPrevention's (CDC's) Vessel Sanitation Program, said at a press briefing lastweek that recent cases of Norwalk-like virus (NLV) infections have spread fromperson to person rather through contaminated food. He said it is safe forvacationers to go on cruises if they take precautions against the virus.

"We feel strongly this is predominantly person-to-personspread through hand-to-mouth activity, and all this makes it a little moredifficult to control, but that it is perfectly safe to go on the cruiseships," Forney said (as quoted in the briefing transcript). "Becausewe're dealing with person-to-person contact and spread, the best preventivemeasure that we can advise passengers to take is frequent and thoroughhandwashing with warm water and soap, wiping your hands off, and keeping yourhands out of your mouth."

Forney also said the CDC had no specific numbers yet, but itappeared that the relative number of illness cases on cruise ships is down."If we look at a number of passenger days, with the tremendous increase innumber of passengers over the last couple years, versus the illness and the numberof outbreaks . . . those numbers have gone down," he said.

The CDC held the press conference Nov 27 in the wake of NLVoutbreaks involving about 1,000 passengers and crew members on twoFlorida-based cruise ships. More than 450 people got sick during two recenttrips of the Disney Magic, and more than500 people fell ill during four voyages of the Amsterdam, according to news reports. The vessel operators,Disney Cruise Line and Holland America, canceled voyages so the ships could becleaned and disinfected.

This week, an illness outbreak was reported on anothercruise ship, the Carnival Fascination.CDC inspectors boarded the ship in Miami yesterday after more than 200 peoplegot sick during a weekend cruise, according to a Reuters report. The cause ofthat outbreak is not yet known, CDC spokeswoman Bernadette Burden told CIDRAPNews today.

Forney said the CDC believes the outbreaks on the DisneyMagic and Amsterdam started when people carried the virus on board andthen spread it by failing to wash their hands adequately. "We have lookedvery closely at all of the food handling practices on board these vessels . . .and have found no deficiencies in either one of these vessels that would pointto a foodborne outbreak," he said. Thorough inspections of the two ships'drinking water systems also revealed no problems, Forney added.

At the press conference, CDC epidemiologist Marc A.Widdowson said people can carry and shed NLV without having any symptoms. Inaddition, people who have had symptoms can carry the virus for up to 2 weeksafter their recovery, he said. But there is no evidence of a "carrierstate" in which people host the virus asymptomatically for long periods,as happens with some bacterial pathogens, he explained.

While calling the cruise ships safe, the CDC officials saidthey don't know how long NLV survives on surfaces or even how effectivedisinfectants are against it, because it is so difficult to detect. The viruscould survive for several weeks, said Widdowson, adding, "We don't reallyknow much about this virus's persistence because it's very difficult to detectit, and it's only recently that we've been able to have the tools to start tolook for it in the environment."

In response to a question, Widdowson said tests with"proxy" viruses indicate that chlorine-based disinfectants and someother disinfectants kill Norwalk-like virus. "But I would have to implythat we don't know for sure if they do because of the technical difficulties indetecting the virus on surfaces," he added.

Despite the uncertainty, experience has shown that emptyinga ship of passengers and cleaning and disinfecting it thoroughly is veryeffective in stopping NLV outbreaks, Forney said.

The CDC recommends using an "industrial-strengthchlorine type solution" to disinfect surfaces that may have NLVcontamination, CDC spokeswoman Burden told CIDRAP News. She said the solutionis not the same thing as household bleach.

In other comments, Forney said there was no outbreak ofintestinal illness on the Holland America vessel Statendam, sailing out of San Diego. He said the CDC has beenasked why it was not conducting an outbreak investigation on the ship, butthere were only 10 to 15 illness cases on the ship, too few to represent anoutbreak.