U.S. Centers For Disease Control
And Prevention
Letter On Cruise Ship Norovirus
Dear Mrs. Hamilton,
Sorry to hear of the illness you and your husband experienced. The cruise from 11/18-29 had 1,746 passengers with 21 reporting ill to medical. There were 689 crew onboard with 1 reporting ill to medical. I will attempt to answer your other questions, but I should say first that there are not many absolutes in the scientific data. As for the isolation period, although you can carry viral agent in your stool for periods up to 3 weeks, it's not clear that those viral particles are viable (or can transmit illness) as that time lengthens. It is clear the goal is to keep people in their cabins while experiencing symptoms, because we have confidence the virus is viable during that time. Symptoms can range for 1-3 days, with two being the average. The isolation is supposed to be for 24 hours after the last symptom experienced for passengers and crew who are not food employees. For food employees the period is 24 hours after the last symptom. That is our minimum standard, but cruise lines sometimes go beyond that. For passengers it is difficult to get them to stay put for even the 24 hour period in cases, because they want to move around and go ashore whenever possible.
The crew is not typically used to convey illness information, but the Captain is. We ask ships to inform passengers even before a cruise begins when they have had an outbreak on the previous cruise, but we would not consider the 11/18 cruise an outbreak based on the numbers reported. When numbers alone are considered we have used 3% among either passengers or crew as an outbreak, especially if 3% or more have diarrhea often enough.
Most ships begin an outbreak prevention and control program when medical receives gastrointestinal illness percentages above 1%, and the heaviest controls begin at 2% illness levels. We have been in contact with NCL to examine log data from the cruise and the cases which reported on this cruise, but we did not investigate it beyond that. We use a number of factors when determining when to physically send a team out to a ship for an in-port or sailing investigation. Three percent illness on a 7 day cruise is the standard value used in outbreak assessments. We actually have been evaluating other outbreaks over this sailing period in other States. We are a small program and can't visit every ship experiencing an outbreak, especially when we are seeing 5 per week.
I can't answer the medical record question, but it sounds incorrect to me. Don't see why they wouldn't release it to you. I thank you for the information you provided and hope you and your husband are at least feeling better.
Regards,
CAPT Jaret Ames
Deputy Chief,
CDC
Vessel Sanitation Program
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