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CDC Telebriefing Transcript
Update on CDC Outbreak Investigation of Norwalk-like Viruses on Cruise Ships
December 12, 2002
CDC MODERATOR: Thank you, Kim. And good afternoon everyone, and thank you for participating.
This afternoon we would like to hold a brief discussion in reference to an MMWR article in this week's report in reference to gastroenteritis associated with noroviruses on cruise ships. There has, as you know, been a lot of interest in this issue, and joining me this afternoon we have Dave Forney, the Chief of CDC's Vessel Sanitation Program. Along with Dave, Elaine Cramer, a medical epidemiologist with the Vessel Sanitation Program, and Dr. Marc-Alain Widdowson, also a medical epidemiologist here at CDC. This afternoon we will be discussing the MMWR article. In addition to that, we will also discuss a report of statistics as to work that's been done by the Vessel Sanitation Program to monitor and track gastrointestinal illness.
We will begin with a brief update from Mr. Forney as to outbreaks and reports of situations that have occurred with gastroenteritis aboard several cruise ships. Upon his brief comments, we will then turn the discussion over to Dr. Cramer, who will give a brief summary of the MMWR article, and then she will also give a brief summary of the information in reference to the statistical data that she has done on reference to illness aboard cruise ships. Dr. Widdowson will be joining us for question and answer. If there are questions specific to Norwalk virus on land versus cruise ships, we've asked him to join us in his assistance to help clarify the differences between what we've seen on cruise ships versus what has been seen on land. So first we will begin with Mr. Forney.
MR. FORNEY: Good afternoon. Thank you, Bernadette.
What I'd like to do is go over an update on the outbreak investigations that we have been conducting. These will be as of the numbers that we have from close of business yesterday. For the Holland America Amsterdam, as most of you know, the Amsterdam returned to service on December 1st, and completed it's 10-day cruise, the first 10-day cruise after they were out of service for cleaning and disinfection, returned in December 11th. They reported to us on a daily basis throughout that cruise, telling us when anybody became ill and reported to the medical staff. And for that 10-day cruise, at the end of the cruise they had reported 10 passengers out of 1,190 passengers, having a gastrointestinal illness, and 2 out of 577 crew members. So these numbers we think reflect all the work that they did in cleaning and sanitizing the ship, and they're continuing in service now, and we really do not expect to do any follow up with that vessel. We did have the epi investigation conducted on one of their first cruises where we identified it, and that actual report is in the process of being written, and when completed will be on our website.
But at this time we're not requesting any special follow up on subsequent cruises.
For the Disney Magic, they are into their cruise following their being out of service for a week for cleaning and disinfection, and as of today's date, they are reporting 25 passengers out of 2,153 passengers that have reported ill with a GI illness and none of the crew. They have 1,026 crew numbers on board. None have reported any illness at all. So they are continuing with their cleaning and disinfection during the cruise and will be reporting to us on a daily basis.
The Carnival Fascination, which had roughly 200 cases of GI illness for their cruise December 2nd, have--actually are in their third cruise following that. We did monitor them closely on a daily basis for the two subsequent cruises, and they had some illness on board, and we note that in our report on our website. They had 13 passengers and 12 crew for the cruise immediately following their outbreak, and they had 6 passengers and 7 crew for the second cruise. So they've gone through two cruises with basically returning to what we would consider background levels for that vessel, and no additional follow up is planned.
When we had originally boarded the vessel on December 2nd, we did collect some water samples and some food samples. The water samples that we collected were tested for a variety of organisms, and those were all negative and the food samples are still pending. But again, we do not plan any additional follow up at this time.
The other vessel that we have talked about in the past was the P&O ship from the U.K., the Oceana, which sailed out of Port Everglades, Fort Lauderdale. On December 7th we did have CDC staff board the vessel down in Barbados with two epidemiologists and one of our mental health officers. They are in the process of conducting a survey of a sample of the passengers and all the crew in an effort to determine how the outbreak began and what particular activities may be leading to person to person spread aboard the ship. We did have stool specimens collected. These were sent to the lab here at CDC in Atlanta, and were received day before yesterday, and so the lab is in the process of analyzing those samples, but it may not be till late tomorrow before we get any results.
As of this morning, in talking with the vessel, the medical staff has notified CDC that 269, that's 2-6-9, of 1,862 passengers, and 24 of 8-7-1, 871 crew, have reported to the ship's infirmary with gastrointestinal illness. And again, all of these passengers originated in the U.K. and flew to the ship on chartered aircraft from the U.K.
That is the update on the ships that we've been tracking over the last several weeks. Again, we're working closely with them, specifically the Oceana right now, and monitoring their cleaning and disinfection protocols on board the vessel.
If things change and as additional information comes up, we will continue to post that on our website.
And I think, Bernadette, that's kind of a wrap on what we had to do on the update.
CDC MODERATOR: Okay. Thank you very much, Dave.
Now, we will hear from Dr. Elaine Cramer. She is a medical epidemiologist with the Vessel Sanitation Program. Again, as I said, she will be providing a summary of the MMWR report as some as summarize her findings in reference to statistics and gastroenteritis outbreaks aboard cruise vessels.
DR. CRAMER: Thank you. Good afternoon.
In today's MMWR we detailed surveillance data that were collected from January 1st to December 2nd, 2002 by CDC's Vessel Sanitation Program. And those data were collected from cruise ships that sail into U.S. ports with foreign itineraries. In 2002, up until December 2nd, we received reports of 21 outbreaks on 17 cruise ships that met the case definition of an outbreak of acute gastroenteritis.
And for the purposes of our surveillance system, we define an outbreak as acute gastroenteritis among either 3 percent of passengers or 3 percent of crew. And we define gastroenteritis as 3 or more episodes of loose stools in a 24-hour period, or vomiting with one additional symptom, such as abdominal pain, cramps, headache, myalgia, fever. It's important to note that this case definition was expanded in 2001, and this differs from surveillance that was conducted from 2000 and earlier.
So our MMWR describes 5 of the norovirus outbreaks that occurred during July 1st to December 2nd. Of the 21, 9 of those were confirmed to be associated with norovirus. Of the 5 outbreaks the percentages of passengers who were ill with gastroenteritis ranged between 5 percent of passengers and 41 percent among the 5 ships. And the crew illness ranged between 1.5 percent and 5.3 percent. Of those five vessels, three of them voluntarily withdrew the vessel from service for one cruise in order to aggressively sanitize and disinfect their vessels. This MMWR emphasizes the fact that it's very easy for Noroviruses to be transmitted from person to person, especially in a closed environment such as a cruise ship, which can often result in large-scale outbreaks.
And we emphasize that ships need to practice basic food and water sanitation measures as well as control efforts through prompt disinfection of the vessels. We also recommend isolation of ill crew and whenever it's possible passengers for 72 hours after their clinical symptoms disappear.
And as well we recommend suitable disinfectants for efforts to eliminate
If you want to see the details, you'll be able to see the MMWR report on the web, and details of individual cruise ship outbreaks will be available there of the five that I describe.
So that's it for the MMWR.
Bernadette, would you like me to move on to the ADAPM article?
CDC MODERATOR: Yes, please. And after that I'll give them some
information as to how to reference and I'll locate all of what you discuss.
The surveillance definition was slightly different before we implemented an electronic reporting system. So the definition of a case of gastroenteritis was narrower for this particular study. And in this study we obtained data from individual ship inspections from 1990 through 2000, and in this study we wanted to evaluate outbreaks over time. And we defined an outbreak as the same as in the MMWR, where at least 3 percent of passengers and crew are ill with diarrhea.
And for the purpose of this analysis, in order no compare with previous published data, we restricted our analysis to outbreaks on cruisers that had at least 100 passengers aboard, in order to reduce the possibility of inflated attack rates, and also we limited cruises to three to fifteen days in duration.
What we found was that there was a steady decline in the incidents of outbreak-related illnesses among passengers, compared with previous studies in previous years. And the data show that between 1986 and 1993 as was reported by Denise Koo in JAMA, there were 1.4 outbreaks per 1,000 cruises. In our study we found between 1990 and 1995 the actual absolute number of outbreaks increased to 6.27 outbreaks per 1,000 cruises. And between 1996 and 2000 that settled at 3.7 outbreaks per 1,000 cruises.
However, in order to factor in the number of passengers at sea and also control for cruise length, we use a denominator of 100,000 passenger days. And when we actually factor in those two elements, what we found was compared with previous years, there was a steady decline in outbreak-related illnesses per 100,000 passenger days. So compared with 1975 to 1979, there were approximately 27 outbreak-related illnesses per 100,000 passenger days. That fell in the period 1980 to 1985 to 8 outbreak-related illnesses per 100,000 passenger days.
Denise Koo reported in 1986 to 1993 6 outbreak-related illnesses per 100,000 passenger days. And in our study, the outbreak-related illnesses per 100,000 passenger days. And between '96 and 2000 3.5 outbreak-related illnesses per 100,000 passenger days.
So for over the ten-year period there was a steady decline. And because 2002 is not finished yet, we'll be calculating those data for the last two years, using our new surveillance system.
So I think that summarizes the outbreak-related data.
CDC MODERATOR: Okay, thank you very much, Dr. Cramer. Dr. Cramer's findings will be available on our website on the vessel sanitation page, in addition to the update that Mr. Forney provided of the cruise ship data. Her findings will be published in April of 2003 in the American Journal of Preventive Medicine. The findings also will be available later this month on the Journal's website. For additional information about that, you can contact their editorial office at area code (619) 594-7344.
Today, her findings, as I said, as to what we reference will be available this afternoon, we're hoping within the hour at the CDC website. Let me give you that web address at this point. It is www.cdc.gov/nceh/vsp. That is the vessel sanitation page. And again, as I said, her findings will be available.
We're now going to open it up for questions. If there are any additional questions beyond what we are able to cover today, please feel free later this afternoon to call the CDC Press Office at (404) 639-3286. Kim will now take questions.
AT&T MODERATOR: And if you wish to ask a question, please press the '1' on your touchtone phone. You'll hear a tone indicating you've been placed in queue. You may remove yourself from queue at any time by pressing the pound key. If you're using a speaker phone, please pick up your hand set before pressing the number.
And we do have over half a dozen questions in queue. So if you could please limit yourself to one question.
We'll go with Miriam Fulcum with CNN. Please go ahead.
QUESTION: Hi. This is for both doctors. I notice that this MMWR mentions the Alaskan cases which we really haven't heard much about in the media, and you mentioned the 200 and I think it was 69 folks on the Oceana. Can you give me a frame of reference? What's a normal amount of GI incidences on a cruise that has 1,800 to 2,400 passengers on? Just so we know, have something to compare this to. And can you just give me a little bit more detail as to how the amount of Norwalk-like virus increases and decreases over the years?
CDC MODERATOR: Dr. Cramer?
DR. CRAMER: This is Elaine Cramer.
I think the issue of the rise and fall of norovirus is better addressed by Dr. Widdowson. But in terms of the baseline incidence of diarrheal disease, which is really what you're getting at--I also include those data in this publication with the American Journal of Preventive Medicine. And what we did was we actually calculated background incidence rates. And for an average cruise of the size you described we're looking at--depending on the itinerary, but approximately 2 cases among passengers per 7-day cruise.
AT&T MODERATOR: And our next question is from Denise Grady with the New York Times.
QUESTION: Thank you. I'm looking at the MMWR report on Cruise Ship C. And I see that there is mention made here of a possible link to food, lunch served at embarkation. Now, we've been hearing all along that there were not--it was thought there weren't links to food or water served on the ship, people were bringing it on person to person. This seems to be different. So could you address that, please?
CDC MODERATOR: Dr. Cramer?
DR. CRAMER: Yes. When we do analysis looking at risk factors, we use odds ratios in order to calculate the odds of illness associated with individual risk factors. In the cruise ship that you describe, it's true the odds ratio was 2.4 in association between illness among passengers and lunch that was served at the embarkation buffet. It's difficult to know what that represents. It's certainly possible that there was an infected food handler, or that there was a food item that could be implicated. However, all we could do with this particular association was implicate a meal. We were not able to be more specific than that.
CDC MODERATOR: All right. May we have our next question, please?
AT&T MODERATOR: Certainly. Susan Candiotti with CNN. Please go ahead.
QUESTION: Thank you. Unless I missed it, you gave us the numbers so far for this year the number of outbreaks. How does that specifically compare to the previous year and to what do you attribute any increase or decline for that matter?
DR. CRAMER: Last year in 2001, by using the same surveillance method, electronic reporting system, we detected 7 outbreaks using the same inclusion criteria, and 4 of those were confirmed positive as norovirus. It looks as though there has been a change between 2001 and 2002, but two points to not make a trend, and so it's difficult to know whether that is in fact a trend. And what we'll really have to do is use denominator data. In other words, calculate rates using 100,000 passenger days in order to really affect a comparison. And we will be doing that.
To the second part of your question, certainly this year it's possible that what we're seeing is a true increase in the number of outbreaks, and we won't know whether--once we factor in the increase in number of ships at sea and the increase in passenger embarkations, whether that disappears, but it's also possible that with our new more sensitive surveillance system, with an expanded case definition, that we're detecting more outbreaks. And also we have more advanced laboratory techniques. We have more sensitive immunoassays, and that certainly helps us to identify outbreaks as norovirus, where in the past we could not do so specifically.
AT&T MODERATOR: And our next question is from Tom Watkins with CNN.
QUESTION: There seems to be some disagreement among cruise ship owners as to whether it's necessary to take a ship out of service for a few days to stop an outbreak from continuing in a second voyage. Does CDC have any recommendations on that?
CDC MODERATOR: Dave, would you like to respond?
MR. FORNEY: Yes, sure. We do not have any specific recommendations on exactly when it's appropriate to take a ship out of service. We take into account the length of the cruise, somewhat the itinerary. We look at the epi curve throughout the duration of a cruise. And all those would be factored in as far as the cleaning and disinfection protocols and how well those are being carried out. All that will be factored in to making that decision.
AT&T MODERATOR: And our next question is from Diana Watkins of WTBJ. Please go ahead. Diana Watkins, your line is open.
Okay, we'll move on to Robert Johnson with the Orlando Sentinel. Please go ahead.
QUESTION: If Dave Forney could try to address this question. Dave, with respect to the Disney Magic, and if I understood you, the 25 passengers on that vessel that have been taken ill this week, could you describe your reaction to that number? Are you disappointed, surprised? Is there still more work to be done? Could you put it concisely on how you feel about the current situation there? You gave them a clean bill of health on Saturday, and I guess maybe the best way to say it is, do they still have a clean bill of health?
MR. FORNEY: They do. And I think, I mean we've been in contact with the Disney staff on a daily basis. Again, reiterating what disinfection protocols are doing and how it's being monitored on board the vessel. We're also looking at the information provided by those passengers who are ill. And in this case, clearly there were 4 or 5 passengers who actually disclosed as being ill the day they got on the ship. Disney is trying to screen passengers before they get there and before they get on the ship, but the only way you can screen a passenger is to ask them whether or not they're currently ill or have been ill in the last couple days.
So ideally, yes, we would like to say that there is no illness. We would like to say that for every vessel that's out there, but we know from our data that people do get ill, and they do present on the ship ill when they get there, and I think that has some influence on the Disney numbers for this week.
AT&T MODERATOR: And our next question is from Thomas Staghorse [ph] with the Sun Sentinel. Please go ahead.
QUESTION: There's apparently been an outbreak of this Norwalk-type virus in Toronto. In a story that ran earlier this week, the chief of the microbiology department at the University of Toronto was suggesting that the virus may have mutated and that it may somehow be better able to transfer from person to person. Is CDC looking at that possibility? Is there any evidence of it?
CDC MODERATOR: Dr. Widdowson, would you like to address that?
DR. WIDDOWSON: Yes, of course. What we see with this virus is there are many, many different strains within the group of noroviruses, and certainly we seem to see--in the past we seem to see one strain that will predominate for a time of being, for a temporary period, and then will seem to fade away again. Now, quite why that happens, we don't actually know. Some people are looking at seeing specifically what the differences in the sequence, what difference in the (?) fingerprinting mean in terms of a structural device, and it may mean that it can be more transmissible, but (?) a bit of an open question.
CDC MODERATOR: All right, thank you.
AT&T MODERATOR: Our next question is from Jane Ingel with the LA Times. Please go ahead.
QUESTION: Hello. This can be addressed by Dr. Cramer I believe, and it's--and it is--I see various percents defined as an outbreak on your website and in some of the other CDC material. Sometimes I see 3 percent. Sometimes I see 2 percent also. And I wonder which one is the right one and why we may see more than one figure on the website?
And related to this, Dr. Cramer had mentioned that there had been--that there had been revisions in the definitions of outbreaks over time that might affect these stats, and I wonder if she could explain that a bit more.
DR. CRAMER: Yes. Prior to 2001 we had a narrower definition of what we called gastroenteritis. We limited our definition to strictly diarrhea, which is 3 or more episodes of loose stools in a 24-hour period. But gastroenteritis can also be characterized by vomiting and additional symptoms. And we often see--certainly with norovirus we see a great number of passengers who experience vomiting as well as diarrhea.
And so in order to improve sensitivity of detection, we expanded the definition, and in numbers at the beginning of 2001 when we implemented our new electronic reporting system, which has now been in place for almost 2 years, and so now the definition is expanded slightly to not just diarrhea with 3 or more episodes of loose stools, but that as well as vomiting--it could be that or vomiting, plus one additional symptom such as abdominal cramps, headache, myalgia, which is muscle aches, or fever.
And what you see when you see 2 percent or 3 percent--I understand the confusion--2 percent is our very sensitive trigger to commence a dialogue with the vessel about what their experience is, and make contact with the infirmary and find out the characterization of illness and to provide assistance and collaborate with the cruise line and cruise ship in order to try and characterize what they have on board and intervene early on and effect public health action.
At 3 percent, that's our definition of an outbreak. So 2 percent is the start of a dialogue and 3 percent is an outbreak. But an outbreak, usually proportions is somewhat limited. In other words, it's really a springboard to individualizing our approach. So for instance, you could imagine on a vessel that only has 100 passengers, 3 percent is 3 people who are ill, and so it's not always appropriate to respond in exactly the same way each time.
AT&T MODERATOR: Our next question is from John Lowerman with Bloomberg News.
QUESTION: Yes, thanks for taking my question. I have a question for Dr. Cramer. It sounds as though you're looking at these--I don't know if you want to call them trends--infections in two ways, both as a percentage of the number of cruises that take place and a percentage of the number of passenger, you passenger days. And is this something that you're still not sure which is the better measure of whether this is more of a problem than it used to be, or whether there is actually--do you have any idea of which of these is a better measure of whether this is a more significant problem than before? I don't know if that's clear enough for you.
MS. CRAMER: I can work with it.
Well, actually no. When we do statistics, we like to control for things that make comparison difficult. In other words, we like to be able to compare data in a valid and sound scientific way. And so this is why we use denominators. And whether we use a denominator of 100,000 passenger days or outbreaks per 1,000 cruises, I suppose it's a different way of looking at the data. But I don't think that one method is more revealing than another.
This is pretty standard and we've been using these types of denominators since the program began in the mid-70s.
CDC MODERATOR: Our next question is from Larry O'Neil with Metro Network. Please go ahead.
QUESTION: Yes. Mr. Forney, I'm wondering judging by the numbers then that you read off earlier, would you consider that most of this outbreak, as we call it, has passed, and that the worst is over. And how quickly could something like this ramp up again, the way we see these numbers that we saw two weeks ago.
MR. FORNEY: Well, we would hope on a daily basis to say there are no outbreaks and the outbreak is over. But we can't predict that any more than we could predict the number of outbreaks we've had in the last month. I mean they came up very, very rapidly. So there is really no way for us to predict. Although I think that as sensitive as our surveillance is, the surveillance on board the vessels is probably even more sensitive now, and also the awareness among passengers.
So I think we'll find if anybody is feeling ill at all, it will be reported to the medical staff onboard the ship, and we'll have even a more sensitive indication of what's going on.
CDC MODERATOR: We have a question from Carolyn Brown with Cruise Critic.
QUESTION: Yes. Hi. The question I have is, there was an incident I guess Tuesday in which a cruise ship anchored at St. Martin, and the officials there were leery of letting passengers on shore. And I just wanted to ask--I'm not sure who the right person is--how are the Caribbean Islands handling this, and will passengers on cruise ships likely be forced to stay on board? I know there was a Cozumel and a Grand Caymen problem with Disney way in the beginning. But this one is the Oceana. I don't know if I make any sense. But anyway I just wanted to address that.
MR. FORNEY: Sure, I'll be glad to address that. Specific to the Oceana in St. Martin, there was a reluctance initially by the Port Health Authority to understand the nature and extent of the illness onboard the Oceana. And the initial Port Health had to go up to a much higher level within the government for a decision on whether or not the ship would be allowed to disembark passengers.
At the same time there were many other ships there. So the only way that the Oceana could have brought off passengers to the shore was an anchoring out and tendering the passengers in, and they physically did not have time to be able to wait for a decision from one of the government officials and then release the passengers and tender them into town and back. So they elected to pull up anchor and sail on.
We have had multiple discussions with various Port Health officials in the Caribbean. Many were concerned because all they had heard was that there was this mysterious illness onboard the vessels. We've tried to explain again what the illness has been and how common the illness is, with an estimated 2 million cases in the U.S. and in situations where I've talked directly with the Port Health Authorities. After they understood that is has not become an issue.
CDC MODERATOR: We have a question from Mark Kaufman with the Washington Post.
QUESTION: Yes. You had given some rough comparisons in terms of trends on the number of outbreaks in cruises. But you also described the number of passengers affected per 1,000, but those numbers seem to end in the year 2000. Do you have any early estimate as to whether or not that number will also be changing? Is there a trend in that, in addition to the trend in the actual number of outbreaks?
MS. CRAMER: You're right. Our analysis of outbreak-related illnesses using a dominator of 100,000 passenger days ends at 2000. Those are the data that will be published in the American Journal of Medicine.
We haven't yet finished our analyses using the same denominators for 2001 and 2002 because this year is not over yet. And certainly I won't speculate as what that trend will look like in comparison. We only know at this point in time what the absolute numbers of outbreaks are, and it may or may not reflect an increase in outbreaks per 10 million passenger days or per 100,000 passenger days, once we factor in cruise length and passenger loads.
CDC MODERATOR: And our next question is a follow-up from Susan Candioti with CNN.
QUESTION: Thank you very much.
Well, this St. Martin business I had not heard about. Have you heard about this from any other cruise ships that were presumably sick or well, for that matter.
And number two, I know you're trying to limit us to one, but one answer prompts another question: You've talked about sick cruise ships. What about how this compares to the Norwalk virus on land.
And finally, what is that we are supposed to tell people. I know this is a three-parter. Do you take a cruise or not, because I know I am asked on a daily basis by people out on the street, "What's going on? Should we be going on these cruises?" They're concerned about whether there's something odd about this Norwalk virus and/or other gastrointestinal illness outbreaks on cruise ships.
CDC MODERATOR: Dave, could you address our first, and the third part of her question? And Dr. Widdowson weigh in on the reference to the issues surrounding land? Hello?
DR. Widdowson: That's fine for me.
CDC MODERATOR: Mr. Forney?
MR. FORNEY: I'm sorry. I was being good and had my mike muted.
The first question was, as far as any other problems with cruise ships in the Caribbean. You know, I have not heard of any. I mean we have dealt with Disney on this, and we dealt with the Oceana the day before yesterday on this. And I have not heard of any other concerns or issues raised by the other cruise lines. Number one.
Number two. Is it safe to go on cruise ships? I will reiterate what I've
said all along. And I think it is absolutely safe to go on the cruises. We
have continued to work very closely with the industry in monitoring illness.
I think people need to realize, again, we're dealing at least confirmed in a
couple cases with
But also people need to realize that gastrointestinal illness is not a reportable illness in the U.S. Whereas for the cruise ships, they have to report, by law, every single case of GI illness that meets the case definition on a cruise. And they must do that every time they come to a U.S. port. They must file that report even if he number is zero. So we're capturing 100 percent of what they report, and, as we have stated, the reporting criteria is very, very sensitive.
So there is a bias there, just because they have to report it, and we capture the information. But all the investigations we have done to date have clearly pointed to this person-to-person contact. We do know that people are still boarding ships, that become ill on the first day or present on the first or second day of the cruise, and then failed to disclose that, "Well, yes I was sick before I left home and got on the ship."
I think we would all understand that because people plan to go on these cruises for a long time, but as a public health official I think that these people contribute to the problem.
And Dr. Widdowson, you may want to address again some of the land base site.
DR. Widdowson: Yes. But I can sort of [inaudible]. I mean I think it's critical to emphasize the fact that cruise ships are not weird in any way, and nor is the virus or even a strain of the virus that we're seeing on these cruise ships weird in any way. As Dave mentioned, the Noroviruses are probably the most common cause of gastroenteritis. I think it was 2 million cases that were there, so that's 2 million cases annually in the U.S.
And we don't have a routine surveillance system for them. And when we do have them, well we do have a surveillance system such as the VSP's cruise ship surveillance, we find a lot of it. So a large part of what we're seeing now is because we're looking for it.
But the other thing is that Noroviruses we know from epidemiology not only are they extremely common but they're also very capricious. And you get these sort of outbursts and outbreaks in different settings on land as well. Certainly the [inaudible] at the moment have had several problems with hospitals being closed, as a previous caller mentioned in Toronto, the UK also, and there are some reports at the moment in the U.S.
I stress anecdotally that nursing homes may be having an increase. But because we don't have a surveillance system, we can't tell.
CDC MODERATOR: We have a question from Jane Engle with the LA Times.
QUESTION: Yes. Thank you. This could be for either Dr. Cramer or Dr. Widdowson.
In looking at the figures on the percentage rate of outbreak passengers versus crew, I noticed that it seems pretty consistently the infection rate among crews seems to be substantially lower than that of the passengers. And I wonder if you could address why that might be so.
CDC MODERATOR: Dr. Cramer?
MS. CRAMER: I think it's a good question. And there are a couple of possibilities. One is that illness may very well circulate among crew that is either undetected or asymptomatic. Or it's possible that there are dysincentives for crew to present to the infirmary with illness. And so we're not really sure.
And the other possibility is in fact that passengers are more susceptible than crew members. Mark, do you want to say anything about that?
MR. FORNEY: Well, Elaine, let me say something real quick on that too.
CDC MODERATOR: That's Dave Forney.
MR. FORNEY: Yes, this is Dave Forney. Thank you. In the early days of some of these outbreaks on the ships, we actually looked at the crew members who were becoming ill, what type of work they did. And we found specifically on the Rhinedam and in the early days of the Amsterdam, that crew members who became ill tended to be crew members who had jobs that put the in a lot of contact with passengers. And the crew members who were down in the ships, who really did not have any contact with passengers were much less likely to become ill. Which is, again, one of the things that tended to support our conclusion that this was predominantly a passenger problem, and it was probably being passed from passengers to crew.
MS. CRAMER: We also found, however, that when we surveyed all of the crews, that there were a significant number who had not reported to the infirmary, although they were required to by virtue of being employed by the vessels.
AT&T MODERATOR: And at this time we don't have any further questions.
CDC MODERATOR: All right. Thank you very much, Kim. Just a few housekeeping matters before we conclude.
First, let me give you the spelling of each of our participants names as well as their titles. Mr. Forney, again that's D-a-v-e, F-o-r-n-e-y. He again is Chief of CDC's Vessel Sanitation Program. Elaine Cramer, that's E-l-a-i-n-e, Cramer, C-r-a-m-e-r. Again she is a medical epidemiologist with CDC's vessel sanitation program. And finally, Mark Elaine Widdowson. That's M-a-r-c dash A-l-a-i-n, last name Widdowson, and I hope I'm correct here, doctor, W-i-d-d-o-w-s-o-n. He also is a medical epidemiologist with the CDC.
I would like to finally make everyone aware that of the two locations on our website where both the surveillance numbers that Dr. Cramer has referenced is located, in addition to today's update from Mr. Forney, if you go to our website again at cdc.gov/nceh, that is for the National Center for Environmental Health/VSP for Vessel Sanitation Program. The first link, the update of outbreak investigations will provide you the details that Mr. Forney provided. In addition, the surveillance numbers that Dr. Cramer referenced, if you look to the VSP content link, the disease surveillance and outbreak investigations link will contain the information. As she said earlier, her findings will be published in April of 2003 in the American Journal of Preventive Medicine. Later this month, her findings will be posted on their website. If you have questions for the American Journal of Preventive Medicine, they can be contacted at (619) 594-7344.
And finally, are there are any wrap-up messages or information you'd like to provide, Mr. Forney?
MR. FORNEY: I think we've pretty much covered it, Bernadette. Thank you.
CDC MODERATOR: Okay. Well I'd like to thank everyone for their participation. Upon conclusion of this call, if there are any further issues that need to be addressed, again please contact us at the media relations office at (404) 639-3286. And again, thank you very much for joining us this afternoon.
This page last updated December 12, 2002
Department of Health and Human Services