SARS Home

CDC Telebriefing Transcript

SARS: Genetic Sequencing of Coronavirus

April 10, 2003

DR. JULIE GERBERDING, CDC DIRECTOR: I'm going to continue with our regular updates on the SARS situation. There are folks who are calling in on the phone so we'll rotate back and forth from the reporters who are here in the room and the reporters who are on the phone.

For my opening remarks, I'm going to focus on basically the update on what's happening internationally and domestically as well as the articles that were published today on the Internet version of the New England Journal of Medicine that described the virology, progress that we've made so far.

As of today, the WHO is reporting 2,627 cases of SARS, plus we have 166 cases in the United States from 30 states, that are under investigation.

Domestically, we have 60 cases that have been hospitalized, ever. We have four individuals who are currently hospitalized. We have a total of 33 out of the 166 people who have ever had pneumonia, and we've had one person who's required ventilation, and to date, no deaths associated with SARS in the United States.

We have been working really hard to try to keep you up to date on the information as it emerges and I just want to take a minute to, first of all, appreciate the interest that the media has had in this issue but also to acknowledge some of the response that CDC has been making.

We have received over 13,000 inquiries about SARS from around the country on our hotline. We have conducted an international satellite video conference for clinicians, globally, that included CDC experts, WHO experts, as well as clinicians from Asia, and that video conference has been accessed by more than 40,000 clinicians, internationally, to help get the word out about SARS.

We've also received numerous consultations from clinicians, domestically, on our clinician hotline and continue to monitor the very high number of Web hits that we're getting on our Internet.

So we are still working hard to try to get this information out and, again, I just appreciate that the interest that the media has shown and the assistance that you're giving us in getting the story out straight.

There are some very specific issues that are of concern to CDC right now. One is that we are hearing reports, internationally, about some stigmatization that's occurring among people in the Asian community.

It's very important that people appreciate that this is a respiratory illness caused by a virus, probably a new virus, and is a disease that is an infection of great medical consequence but it is not a disease that is in any way related to being Asian or to the fact that Asia happened to be the place where we first recognized cases.

So we want to ask people's support and help in appreciating how difficult this is for the affected people and how we really need to take the high road here and recognize that this is a time when all of our communities need support and empathy, not stigma or bias or shunning that has been reported in some international press.

In part to address that, CDC has established a community outreach team and we are working with various communities, in particular the Asian community, to understand what are the issues, what are the best ways of providing information to the community and languages, and formats that are accessible to the individuals who are concerned or affected by this problem, and we will be continuing to work aggressively to provide factual information and hopefully reduce some of the stigma that could evolve.

We are very concerned today about reports of suspected SARS cases that may be related to community transmission in Florida. The Florida health department as well as the local health departments in the involved communities have been doing an excellent job of assessing these situations.

One situation, in particular, involved a person who traveled to Asia and developed an illness consistent with SARS. In the very early phases of that illness, the individual did go to work, and during the active monitoring of contacts that the Florida health department is conducting, an individual in the workplace who has respiratory illness was identified. So that worker is now on the list of suspected SARS patients but it's far too early to indicate whether any of these individuals actually has SARS.

There's certainly no indication of spread beyond that point and the health department is aggressively taking the appropriate steps to make sure that they have communicated with all of the exposed people or potentially exposed people, and are doing the right things to contain any addition spread, should this indeed turn out to be SARS. But it's far too early to say that at the moment.

We are also taking steps today to enhance the guidance for contacts of SARS patients. So later today you will see posted specific information for schools and for workplaces to ensure that should an individual with SARS inadvertently go to the school or go to a workplace, that we have the appropriate steps in place to manage those events, and we will be working with state health officers today, and consulting with them on our regular conference calls, to get input about how to implement a more active monitoring system for contacts of SARS patients, so that we will know not only passively, if a contact develops any illness, but we will proactively be monitoring them or asking them to participate in a monitoring program where their symptoms can be recognized at the earliest possible moment, so that they have very little chance of spreading this infection to anyone else.

In the New England Journal today, the CDC group as well as other laboratory groups are reporting on the advances made in the coronavirus assessment and the virology of case patients.

I want to emphasize that this is still an evolving story and while we are increasingly confident that we are dealing with a new coronavirus, we cannot yet say that this is the definitive cause of SARS.

We had a consultation with experts in virology and in clinical medicine to determine what would it take to say yes, this coronavirus is indeed the cause of SARS, and there are two additional steps that must be fulfilled before we could make that claim.

First of all, we need to unequivocally demonstrate the coronavirus in the affected tissue, i.e., in the lung of patients with the disease, in areas where we would also see inflammation or pneumonia. We've seen the virus in tissue and we've seen evidence of pneumonia but we need to see them both together in the same specimen to really show that the virus is geographically associated with infection.

The second important aspect to prove definitive relationship is that we must have an animal model where we inoculate the coronavirus into an animal, the animal gets sick and develops pneumonia, and then we isolate coronavirus from the affected tissue in that animal model.

CDC has provided our strength of coronavirus to investigators in The Netherlands. They are actively pursuing this animal model and we await, with great interest, their results, to see whether or not this will be a successful introduction and really proof of causality.

When we have that information we of course will be making it available to you.

I think that will be the last formal remark I'll make at this time, but I will open this up to questions and I'd like to start with a question from the telephone, please.

MODERATOR: Ladies and gentlemen, if you do wish to ask a question, please press the one on your touchtone phone.

DR. GERBERDING: Okay. Then we'll just go ahead and take a question from the reporters here. You need the microphone.

QUESTION: I read that the World Health Organization is concerned about the possibility of transmitting SARS through the blood supply.

What can you say about the level of concern of that, and of course the search to develop a test, if it can be transmitted that way?

DR. GERBERDING: Thank you. We have no evidence, at the moment, that this is in any way a blood-borne infection, but any time there's a new viral infection or patients are as sick as these patients, I would have to be concerned about at least a temporary period of time where the virus could be in the blood.

So CDC is working with FDA and the blood banking industry to develop some sensible guidance about deferring donation among people who have traveled to affected areas and could be in an incubation period, and I anticipate that those guidances will be out very soon.

Now, can I have a question from the phone, please?

MODERATOR: Yes. We have a question from the line of Laurie Garrett with Newsday. Please go ahead.

QUESTION: Yes, good afternoon. Quick question. In terms of looking for an animal model, are any of the labs that are going to be working on that, the Amsterdam lab or anyplace else, likely to have and be able to run experiments on Asian species of pigs, and in particular unusual pigs, like the Vietnamese miniature pig and the Chinese guinea pig, and so on?

DR. GERBERDING: Thank you, Laurie. I think right now the focus is on simply fulfilling any animal model criteria for infection. But I think what you are really getting to is the question of where did the virus come from and is this a virus that could have jumped species, so being able to establish infection in an animal model might be a clue to that. I think we're more likely to get at that answer by looking at the virus sequences as the genome emerges, and also identifying animals in Guangdong Province or in other areas where the earliest cases occurred so that we can see if we can locate related Corona virus in any animals species in the region.

Question over here?

QUESTION: Hi, Dr. Gerberding. Thanks for doing this. I have two questions, one relating to Florida. I'm glad you were able to elaborate a little bit more on this co-worker incident, because the Florida Health Department yesterday threw that out and said that's yet another definition of close contact but there was not information.

But given that somebody in the workplace did get sick and that the child in Florida also was in school while he was having slight symptoms--he had a slight cough--doesn't that raise the concern that people are being exposed and don't know it, and what are the guidances going to be that you're putting on the website later today?

And then the other question I have is, you have an updated case definition on the website talking about airport transit as the criteria for being a possible suspected SARS case. Could you elaborate what that means, too?

DR. GERBERDING: Let me speak to the first issue about the definition of community exposure or community transmission. We know, and have known since we first heard about this problem, that most of the individuals involved in acquiring disease from contacts are either health care workers or close family members. And that has certainly been the pattern in the United States, where up until these Florida cases emerged we had seen three cases in health care workers and five cases in close household contacts.

We are most concerned from a public health perspective about spread unlinked to known cases of SARS. And when we see an unexplained case popping up in a school or an unexplained case of SARS popping up in a workplace, that's when we become concerned that our containment efforts have failed and that we are not able to contain this from a public health perspective. We are not seeing that in Florida or anywhere else in the United States at this time. The cases that are under investigation area all linked to a traveler and are within the confines of what we would consider to be related transmission outbreaks.

So first of all, we have no proof that any of these patients have SARS at this point. They haven't been tested and there's a lot of work that needs to be done. If you read the articles in the New England Journal, I think you would appreciate that increasingly it looks like we've done exactly what we wanted to do. We've cast a very broad net around the SARS patients and we're including on our suspected list many patients who don't seem to have evidence of SARS. So as we go forward, we will have a more specific definition that will probably make some of this investigation a lot faster and relieve a lot of anxiety in the community right now.

Nevertheless, look at the globe. We see that it is possible for this virus very quickly to spread under certain circumstances, and whether that is because there are modes of transmission, such as the airborne route, that we haven't identified or documented well yet or because some people are particularly efficient transmitters, we need to be prepared here for the possibility that we will have spread outside of the close family or the health care workers. And that's why we are taking steps today to enhance our monitoring of contacts and to be more inclusive of who is in the contact compartment and to be more proactive about, rather than asking the individual people to contact their clinician if they develop any kind of an illness, that we are going to work with our health departments so that we contact the contacts and check in with them at periodic intervals to identify their health status.

I think this is for us right now in this country a very sensible way for being more aggressive about containment and still keeping in mind the epidemiology as it's unfolding here.

QUESTION: What does airport transit mean? When you list it on the website, what are you talking about? If I'm in the airport with a planeload of passengers returning from the area, am I an airport transit?

DR. GERBERDING: We have concerns that in areas of the world where this disease is being transmitted in the community, that any exposure in a congregant environment could potentially pose a health hazard. And if you are a passenger traveling from an unaffected part of the world, but you go through an airport in a country like, say, Hong Kong, where disease is being transmitted, it's possible that you would come in contact with someone who is infectious. And so we are considering that as a potential exposure as well learn more about how this disease is being spread.

May I take a question from the telephone, please?

MODERATOR: Yes, we have a question from the line of Jeremy Manier with the Chicago Tribune. Please go ahead.

QUESTION: Thanks very much for doing this. Another question about the sequencing which you alluded to a minute ago. How far along is that? I guess it's fairly far along, if not largely done by now. How soon will that be made public to researchers? And also, have other Corona viruses been sequenced entirely so you can compare this to them to see, you know, what it's most closely related to and where it might have come from?

DR. GERBERDING: Thank you. In the New England Journal today there are--the publications include the molecular assessment of the group of viruses that this Corona virus belongs to, compared to the known groups of Corona virus. This sequencing is based just on a component of the polymerase gene. Obviously, we want the whole genome sequence. The laboratories at CDC as well as other laboratories within the collaborating network are very far along on this. We at CDC has made the philosophic decision that when we have the genome and we've validated that we have it right, we're going to make it available in the public domain so that other scientists can use it.

We recognize that there is always controversy about publicizing genetic sequences, and we will of course confer with others to make sure that this is an appropriate step. But our initial philosophy is that the more open and transparent we make the science here, the faster we'll be able to get to a solution.

Yes, over here?

QUESTION: I wanted to go back to Diana's question, if we could, on the blood supply. Is there any way to trace back people who donated blood to see if they had traveled to Asia, and are you recommending to the Red Cross, if that's possible, that they pull that blood off the shelves? And how far back would you go on that?

DR. GERBERDING: I think we need to step back away from this issue and recognize that what we're doing right now is an extra precaution. They have absolutely no evidence in Asia or anywhere that the blood supply has been a source of transmission of Corona virus, and in general that is probably unlikely, although we want to be absolutely sure. We have seen this happen, for example, with West Nile, where we did find evidence that the blood could be a vector under certain circumstances.

So we are not initiating look-back investigations at this point in time. There is no indication clinically or epidemiologically that that's appropriate or necessary. But again, we have an open mind and we will take the necessary steps if the evidence leads us in that direction.

I'll take a telephone question, please.

MODERATOR: Yes, we have a question from the line of Stephen Smith with the Boston Globe. Please go ahead.

QUESTION: Hi, Dr. Gerberding. Good afternoon. I was hoping that you might elaborate a bit further on the issue of community transmission and discuss what you think some of the differences are that have resulted in limited community transmission, or no--as you're defining it--community transmission in the United States; whereas in other settings there has been community transmission experienced. Is it a matter of, essentially, bulk of cases, that there has not been a sufficient number of cases in the United States to result in that sort of transmission? Do you think it has something to do with the variability of the virus? What is your thinking at this point?

DR. GERBERDING: What I'm going to do is speculate, because we don't know the explanation. And one explanation may just simply be we're having very good luck here. But we do have the advantage of recognizing SARS later than many of the other countries where cases first appeared until our public health system and our clinician system, or medical system, have been able to very quickly implement appropriate isolation precautions when we do have suspect cases. I think that's a sign that our public health system is doing what it should be doing; that is, detecting and isolating in very short order.

It's also possible that we've been lucky in the sense that we haven't had here any of the patients who are especially infectious. Again, this is just hypothesis, but there does seem to be a suggestion, looking at the Asian experience and perhaps the Canadian experience, that some patients are particularly efficient at transmitting this virus, for whatever reason, and we haven't had patients in that category here.

And finally, as I emphasize over and over again, we have cast a very broad net here in trying to identify anybody who could possibly have this illness so that we are over-isolating, over-diagnosing, and probably overdoing the whole effort to achieve containment because we would rather make sure that we have everybody who could possibly be a SARS patient in isolation. And as we get more experience with the diagnostic tests or the antibody tests that we have available to us, I think we'll narrow our case list and then we'll have a much better evidence base for understanding the true tendency for transmission and the true numerator and denominator of the frequency that this is occurring.

I should also mention concerns about the potential for transmission without symptoms. This does not appear to be a major component of spread so far, but now that we have these diagnostic tests or these potential tools for epidemiologic purposes, we'll be able to check and see if people are carrying the virus in the absence of having any symptoms. And that may also help shed some light on how this is being spread.

May I take a question from a reporter here?

QUESTION: [Off-microphone, inaudible.]

DR. GERBERDING: Thank you. The sequence is certainly an important aspect of developing a vaccine if we're going to make a molecularly based vaccine. But the fastest way to get from where we are now to a first-generation vaccine is to do the old-fashioned methodology, which is basically growing the virus in a certified cell line, killing it, and then inoculating an animal to see if it offers protection against exposure.

In the best-case scenario, if everything goes well and we have a good system for growing the virus and we have a good animal model for demonstrating that it works, we're still at least a year out from any kind of investigational vaccine.

In terms of antiviral treatment, we're continuing the process in conjunction with our collaborators in the Department of Defense at the U.S. Army Disease Research Institute, and we are disappointed that the early results suggest that Ribavirin is not active in the screening system that they're using. That was reported in today's MMWR. But there are other compounds under evaluation there. And pharmaceutical companies, through the work of Secretary Thompson and the FDA, have certainly agreed to make anything they have on the shelf or anything in the pipeline available for screening in these systems. So if there's something out there that has antiviral activity, I anticipate we'll be able to find it, and that could lead to a treatment. But it's a ways off, and I don't think we should hang our hat that that's going to be the way we contain the problem, at least in the stage we're in right now.

QUESTION: [Off-microphone] But right now, [inaudible].

DR. GERBERDING: Right now, for individual

patients the treatment remains symptomatic, and in addition, sometimes broader spectrum antimicrobial therapy in case they have a completely unrelated illness and could benefit from antibiotics or anti-virals for an alternative diagnosis.

A telephone question, please.

MODERATOR: Thank you. You have a question from the line of Larry Altman with New York Times. Please go ahead.

QUESTION: Yes. Two questions, Dr. Gerberding. First, could you clarify the distinction between your definition of community and the World Health Organization's definition of community because the World Health Organization says their definition is anything other than an imported case is a community case, and the second question is can you highlight the specifics of what is new in your guidelines from today.

QUESTION: Thank you. Yeah, I think there's a lot of definitional issues that are causing confusion. It's probably better not to rely on these jargon terms and instead talk about what exactly it is that we're trying to accomplish and where we need to focus our attention.

We have defined a linked case of transmission as a person who is a traveler from an involved area, who is a SARS case, and then either close household contact, or a health care worker who's taking care of that individual, as being tightly linked to the case.

When you move outside of that immediate environment and you see transmission outside of the home or outside of the health care setting, where we get concerned about transmission in the community and there, additional public health measures may be required, and so that is where we are focusing our new guidance.

What we will be recommending is dependent, in part, on the input that we receive from our state health officers this afternoon.

I was pleased, when I spoke with Dr. Awanabi [ph] from Florida, health officer for the State of Florida, that they are already utilizing some proactive monitoring of contacts in that state. So it looks like this approach may be feasible and as soon as we understand what our health officers are doing and what seems to be working, we will try to formalize that and put the best practice out as a means of enhancing our assessment and early detection of potential symptomatic people.

I'll take a question over here.

QUESTION: Thank you. Doctor, a first question about how the CDC is handling the numerous calls that it's getting, I understand 1500 a day or something like that, how are you dealing with that kind of overload?, and also we've also had a report here that at least one of the cases here in Atlanta, metro Atlanta, was in fact not a SARS case. We just got that from the state health department.

Your concern about having, since the symptoms are so common, your concern about having so many false cases that may arise out of this?

DR. GERBERDING: Well, first, let me say that a false case is a good thing from our standpoint, cause we would rather err on the side of overinclusion than underinclusion, and this has happened several times in the last few weeks and we fully expect this to continue as we use this broad case definition.

With respect to how we are handling the communication challenges that we bring, Dr. Vicki Freimuth  is here today, and largely her emergency communications system has been activated. This is a communications system that we established in response to the lessons we learned in the anthrax attacks and is a organized, cross-discipline communication plan here, at CDC, that allows us to have teams of people who are approaching the needs of individual target audiences.

So we have a group of people who are focusing on the communication needs of clinicians, a group who are focusing on the Internet, a group who are focusing on health officers, and so forth, trying to anticipate and learn from our constituents what their true communication needs are. So there's a lot of outreach going on.

With respect to how we are handling the volume of public inquires, we have established a contract with an organization that is available to provide this kind of information to the public on a not quite 24-hour-a-day basis, but over a long period of time each day, and we constantly provide them with the latest information in a format that allows it to be easily transmitted to the public.

But, in addition, we learn from them. We pay attention to the calls that we are receiving, so that we can identify what are the communication gaps between what we've got out there and what people are asking about, and we work really hard to fill them.

I'll take a question from the telephone, please.

MODERATOR: Yes. We have a question from the line of Jennifer Warner with WebMD. Please go ahead.

QUESTION: Yes. Dr. Gerberding, looking at the New England Journal articles, could you address some of the mention in there of the presence of the coronavirus in the stool of the patients during convalescence, and the possibility that that virus might be transmitted during that route, and there was also some talk about, related to roaches in the apartment complex in Hong Kong, and tell us what that might mean about how the virus is being spread.

DR. GERBERDING: Well, first of all, the epidemiologic evidence, to date, still continues to support the hypothesis that the primary means of transmitting this virus is face to face contact.

Finding PCR evidence of virus in the stool may mean that the virus is in the stool, or it could also mean that the genetic material from the virus is present there. That's two very different possibilities.

The coronavirus family, in animals, often does cause a diarrheal illness, and so it's not impossible that the virus is in fact directly affecting the intestinal tract, and some of our early clinical reports did describe diarrhea or gastrointestinal symptoms. But I think that we have a lot of work to do before we can interpret the presence in stool, and we have no direct or indirect evidence, at this point, that the fecal, oral route, or any other relationship with fecal material, either through cockroaches or sanitary conditions is playing a role in transmission.

That is something that is being investigated in Hong Kong and we look forward to learning more about where this hypothesis was generated.

I'll take a question here in the front.

QUESTION: Can you talk about the significance of the virus being active in the viro cells and also if this virus came from animals or from a recombination of human viruses? Do we know whether it might mutate more?

DR. GERBERDING: Thank you. When we have an unknown situation like an unknown illness, and we're looking for a virus, the scientists inoculate a large number of different kinds of cell lines to try to see if it will grow in anything. In this case the virus did not grow in the things that typically show virus growth but it did grow in this particular viro cell line, which is a cell line derived from monkey cells.

What's interesting about the viro cell line is that it does not have interferon. Interferon is a compound that often inhibits virus growth as part of the natural immune system against viruses, and so that suggests that maybe cells that lack interferon are permissive to the growth of coronavirus, and for whatever reason, we are lucky that the virus did grow in that cell line and that certainly gives us a headstart on being able to produce it in larger quantities for the research and the vaccine development work that will need to go on in the future.

With respect to your second question about either recombination of human viruses or cross-species transformation of the virus, this is a single-stranded RNA virus, so it's wobbly, and by that I mean when it reproduces, it's not necessarily a 100 percent capable of creating an exact clone.

There are very high likelihoods of small genetic changes each time a virus like this divides, and so we would be surprised if we didn't see ongoing evolution in this family of viruses, over time.

Of course of all the different genetic variants that can be created, many may not be virulent, many may not be efficiently transmitted, so it's just impossible to predict what the future may hold. But it is something that obviously will be important to monitor, over time, as this moves throughout the population and particularly as we move toward vaccine development or antiviral treatment.

I'll take a question from the phone, please.

MODERATOR: Yes. We have a question from the line of Jennifer Culman [ph] with KYW TV. Please go ahead.

QUESTION: Hi. Yes; thank you. You had talked, a couple days ago, about diagnostic tests may be getting out to the state level. What's the status of that? Are you moving any closer to that?

DR. GERBERDING: It's very important to distinguish between tests that are licensed diagnostic tests and tests that CDC creates in a public health emergency for epidemiologic purposes or to enhance our understanding of an emerging health problem.

Right now, we have three tests that show a high degree of promise for this particular outbreak and it's possible that any one, or all of these tests could be developed as licensed diagnostic tests in the near future.

But what we have right now is a PCR test which is useful in identifying virus material in the respiratory secretions of patients. The advantage of this test is that it would be positive early in the course of illness.

We also have two different antibody tests. The advantage of the antibody tests is they're generally easier to do, even in developing countries than a PCR test, but the results in a given patient may not be positive until several days have passed after the onset of infection cause the antibody measures the body's response to infection.

These tests right now are being used epidemiologically at CDC. In today's MMWR, we report on the distribution of test results to states that are taking care of a small number of SARS patients, positive test results were provided there, and I think this will be important in epidemiologic evaluation as well as hopefully to the individuals.

But we are having to go through several additional steps before the tests can be widely available in every laboratory or even every laboratory in the Public Health System.

Those steps include, number one, optimizing the methodology so you get the same result every time you do the tests, and we are very far along in that.

Number two, we have to make the reagent. For example, for the PCR test we have to make the priers, and that takes some time, to get enough of the primers produced, in a volume that's great enough to allow widespread distribution.

Thirdly, we have to develop a method that works for every kind of equipment that laboratories might be using.

For example, there are several different equipments that do PCR testing and the protocol has to be optimized for all of them, and then finally, we have to send blind samples out to individuals in the laboratories so that they don't know what the result is in advance, and we can test their proficiency and help validate that they're getting the same results that we are.

We think by the end of next week, we will have all of the protocols developed and we'll be well on our way to producing the reagents, and probably by two weeks we'll have distributed this test methodology to at least many of the laboratories, if not all of the laboratories in the Public Health System.

Independent of that, the FDA is working with us to make sure that we are doing all the things we need to do to be able to license this test and the big issue there is we just have to do it on a lot of control test specimens, a lot of cases that we know have SARS, and then a lot of cases in between, and that really takes some time.

So we're doing it very fast and I know it seems like it's taking a long time, but keep in mind that this is really just 30 days since CDC activated it's emergency response center and began to receive virus specimen.

So this is actually an amazing achievement that our laboratories and other international laboratories are even this far along right now.

I'll take a question over here.

QUESTION: Dr. Gerberding, thank you for doing this. I have two questions. One is on the New York Times report saying that a doctor in Beijing, [Chinese name], [inaudible] even in his hospital are 100 patients suspected with SARS cases. I was wondering if WHO team or CDC experts will do further investigation in Beijing area?

And the second question is WHO's report, it mentioned about possible case in a rural area of China. Will any effort on that?

DR. GERBERDING: Thank you. The WHO team is still in China and they are still working very hard. Their efforts, right now ,have been concentrated in the Guangdong Province.

I think there's great interest in understanding the epidemiology and the disease patterns in other provinces but I don't have today's report from China, so I can't really give you any specific information.

We're all interested, we're all worried, and we hope we'll be able to get some enlightenment soon.

I'll take a phone question, please.

MODERATOR: Yes. We have a question from the line of Elizabeth Cohen with CNN. Please go ahead.

QUESTION: Hi, Dr. Gerberding. Last night, at the elementary school that's attended by the six-year-old boy in Florida who's believed to have SARS, there was a meeting for parents, and the parents were asking the same basic question over and over again, which is this child, the index child, was at the school with symptoms. He's gone, but what if he infected another child who's now asymptomatic but is infecting other children?

They were sort of worried about a kind of chain of transmission. What would you have said to the parents, if you were there last night?

DR. GERBERDING: The first thing I would have said is that I can understand full well why they are concerned. This is still a very new and a very frightening situation and it is alarming to feel like a child in a school system could potentially have exposed your child.

So I would really first try to communicate my empathy, as I try to do with all the people who are dealing with this, and in terms of the risk, the objective risk of spread, I would try to acknowledge what we know so far, and what we know so far is that it is people who are symptomatic who seem to be the ones who are transmitting the infection, and we are not seeing spread from people without symptoms in any of the places, even where we have very good monitoring.

So what we know so far is that asymptomatic people don't seem to be transmitting it but we have to acknowledge some uncertainty and that's why the school and the local health department are taking steps to make sure that there is a monitoring program and that the children in that school are under close observation.

We will also, as I said, work to address this with some additional guidance that we hope to be able to promulgate later today, and we'll be working with the health officers there to make sure that we haven't left any stones unturned.

I'll take a question from a reporter here in the room.

QUESTION: What have you learned from your CDC colleague in Canada, in regards specifically to community transmission? They seem to be having a growing problem there of folks not participating in the voluntary program, report of a student leaving to take a test and then the entire class has to stay home because of that.

And then the other question I have--and I'm sorry to keep going back to the airport transit--from what you described earlier, would that mean that flight attendants should be a little more concerned, or they might need a little more protection?

DR. GERBERDING: With the situation in Canada, I would first of all encourage you to talk with the health officers there because we respect the hard work that they're doing and they really would have the detailed answers to your question.

But I would say that as of this morning at least, our information was that the cases in Canada are still limited to contacts in homes and in health care settings.

What's happened is as people have become ill with SARS they've gone to new hospitals and set up some tendency for transmission to health care workers in the new situation. But they are not seeing unexplained transmission in schools or out of the two groups that I just mentioned there.

With respect to the safety of air travel and concerns of flight attendants, again, we understand how concerning this would be for travelers and crews on these modes of transportation ,and are working with the international union that represents flight attendants as well as other organizations, to make sure that, first of all, we've given people the information they really need to understand what is a risk and what isn't a risk, but also that they have the information they need to protect themselves.

We are also creating a video that will be shown on airlines. It's about a two-minute video that will be available to international flights. It's actually been produced and we're in the process of reviewing it and translating it into the appropriate languages, but this video will be available on airlines to help remind passengers about SARS, what they need to be concerned about, what they don't need to be concerned about.

So we appreciate that there's concern and we're working with WHO and others to try to address it in a sensible way.

I think I can take one last question from the phone, please.

MODERATOR: Yes. We have a question from the line of John Norman with Bloomberg News. Please go ahead.

QUESTION: Hi. Thanks for taking my question. Could you talk about how the state that we're at now with diagnostics, with this test, how does this change things?

For instance, will this change--the state that we're at, will it change the count of patients in any way? Will it change treatment, prevention, in any way? Or are we really, in terms of diagnosis, are we at the same stage that we were yesterday?

DR. GERBERDING: I think we're a little closer to being able to have more specificity about the diagnosis of SARS but we're a long way from being able to do that with the same kind of reliability that we have with regular licensed diagnostic tests.

Now keep in mind, we still have not proven that this coronavirus is the cause or that it's the only cause of SARS, so that alone gives us some room for inaccuracy in what we're doing.

But we also I think have made a great deal of progress and have tested more and more samples now, so we're beginning to get a sense that in the people who have the most classic presentation of severe SARS, who have had the travel history that we're concerned about, these tests are positive, and so that is bringing us much closer to an understanding of what the link is.

We also have people on our suspected SARS list who we include because they technically meet the case definition, but probably in the minds of most clinicians and most epidemiologists, they're not likely to actually be SARS, and we're hoping that the tests results in those people will be negative and that will give us more confidence.

It's an indirect way of saying we've got a lot more to learn but we remain optimistic, and let me thank you for you attendance today and for helping us get this information out and as we learn more we'll tell you more. Thank you.

MODERATOR: Thank you, ladies and gentlemen, that does conclude our conference for today. Thank you for your participation and for using A&T Executive Teleconference. You may now disconnect.

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