SARS Home

CDC Telebriefing Transcript

CDC Update on Severe Acute Respiratory Syndrome (SARS)

May 8, 2003

DR. GERBERDING: Thank you for being here for another update on SARS. Today, I'm going to review some of the information in today's Morbidity and Mortality Weekly Report which has two articles of concern to SARS, one, an update on the status of the investigation in Singapore which provides some very important perspective on lessons learned there, that may be very well applied to other countries, including this one, and then a second article that just describes the current status of the situation in the United States.

Today, WHO is reporting 6,838 cases, 495 deaths in 28 countries, plus 63 probable cases in the United States, including cases among 61 travelers, one health care worker and one household contact that we have described previously.

In the MMWR today ,we provide information about the countries that the 61 travelers had visited prior to the onset of SARS. Those countries include mainland China, Hong Kong, Singapore, Hanoi, Toronto, and 13 individuals who'd visited more than one country en route.

We've had no new United States cases reported in the last 24 hours.

We are very pleased today to be able to announce that we are making the reagent for one of the important laboratory tests available to our state and local laboratory partners. The reagent for the ELISA test, which is the antibody test that we use to create a laboratory-confirmed case of SARS, will be made available, and the states have already developed a great deal of experience with this kind of test.

It's been used for other infectious diseases but this time we have the specific compounds necessary to apply it to SARS. This test will allow us to determine, at the end of the 21-day clinical course, whether or not the patient has developed an antibody to the SARS coronavirus, and if an antibody has been developed, it's a very strong sign that they had coronavirus infection and they are a true case.

If there is no antibody at the end of 21 days, we can't conclude that there isn't SARS, but it makes it less likely, and we're working with our state partners to determine at what point we can reliably rule out the diagnosis of SARS and remove these individuals from the case list.

CDC is also continuing its process of advising travelers to Hong Kong, Toronto and Taiwan--excuse me--Hong Kong, Taiwan and mainland China--let me say that again--Hong Kong, Taiwan and mainland China, about the importance of avoiding unnecessary travel to those regions.

We are also generically alerting travelers to all countries that have ongoing SARS, to be aware of places where SARS could be transmitted and to take steps to protect themselves, which would include primarily not going to health care settings.

Now in today's MMWR, we do discuss, in some detail, the outbreak in Singapore, and there are a couple of important aspects to this epidemic that have important lessons for us.

First and foremost among them is the concept that some individuals are super spreaders. The report describes five individuals who were the source of transmission to a very large number of other people. In fact, overall, these five people infected approximately 144 other individuals.

So we are defining a super spreader as someone who has infected more than 10 people through direct exposure during the course of an outbreak.

Most of the exposed people were exposed in the health care setting.

The other side of this, however, I think is also very important, and that is 81 percent of the people with SARS in Singapore did not infect anyone else as far as we know. So most people don't transmit the infection. Some people appear to be very efficient or effective transmitters. Why there is a difference between those who don't transmit and why some are transmitting with a high degree of efficiency is a question that we don't have an answer to yet.

One explanation may simply be that the people transmitting had a long period of contact when their contacts were not using the appropriate infection control prevention measures, but there may be other factors. Perhaps they had more virus. Perhaps they were more ill or had more coughing. We have a lot to learn about exactly how to account for these super spreaders, and we'll be sure to keep you apprised about this as we go forward.

CDC has investigation teams in Singapore and we continue to work with the government officials there to contain the epidemic. As you know, we have not had any additional unlinked transmission cases in the community of Singapore and that's why there's no longer a travel advisory to that country. But they have still remaining, some hospitalized patients, and so they are continuing their vigilance.

They're continuing to quarantine exposed persons in the community until they are outside their 10-day incubation period. In this report, there was suggestion that the average incubation period was about six and a half days.

WHO has looked at the data on incubation periods for all of the countries reporting to WHO and has concluded that 10 days still represents the best estimate of the maximum period of incubation.

So we are continuing to use 10 days as our period of risk after someone's been exposed to a patient with SARS, and as we go forward, if we learn new information to change that, we of course will work with WHO and others to adjust our guidance accordingly.

I think the last big picture thing to present today is sort of our perspective on where we are today.

We recognize that there are concerns continuing about the possibility of importing SARS, particularly from China and Taiwan, and perhaps Hong Kong, although we are still increasing our optimism about the prospects for containment in Hong Kong.

Our alerting process to incoming travelers continues but that's one in a whole series of steps that are protecting Americans from exposure to SARS.

First of all, the countries that I've mentioned, Hong Kong, Taiwan and mainland China, are implementing extremely aggressive quarantine procedures in their countries. Tens of thousands of people are in quarantine and that is a very important step to protecting everyone from exposure to SARS.

Second, these countries are screening departing passengers for symptoms of SARS or for exposure to SARS.

Third, airline crews are on the lookout for people on planes and ships that have--passengers who have illness.

Fourth, these flights are being met by our quarantine officers at U.S. ports of entry and if there's any concern about an ill passenger, the passenger is being evaluated, and if there's still concern, detained until further information or isolation is indicated.

Finally, all arriving passengers are receiving the health alert to alert them to the importance of seeking medical care if they develop any symptoms.

So there's a whole series of guidance that's in place to protect people and to identify at the earliest possible moment an incubating SARS patient.

We will continue to aggressively take these steps and our situation here currently is that this approach seems to be working.

We know that many returning travelers are volunteering information about their health status and that has probably been our best line of defense overall.

But following that, our health care delivery system has participated in appropriate isolation and early measures to prevent spread.

We are continuing that degree of vigilance and we will continue that prospectively, until such time that SARS is contained everywhere.

So let me just take questions and I'll start with a question from here in the room. Go ahead.

QUESTION: Dr. Gerberding, a couple of points here. What's the timeframe between exposure to SARS and the evidence of symptoms of SARS, and are there any steps being taken to identify possible super spreaders and prevent them from coming into the United States?

DR. GERBERDING: The question you ask first really is the question: What is the incubation period? What is the time from the exposure to the virus and the time in which your symptoms appear? And that period of time is 10 days.

Our information so far indicates that people are not infectious during their incubation period until they develop symptoms of the disease.

That's why we make a big point of recommending that at the earliest sign of any symptom, people make contact with their health care provider, alert them that they have been a traveler, have reason to be concerned about SARS, so that the system can implement the infection control precautions before they get there and then get medically evaluated in person.

So the 10-day period of time is the window, and if you traveled, say, to mainland China, and it's been more than 10 days ago and you haven't become ill, your chances of having SARS from the information that we have are essentially zero, and that's why we use that as our cutoff.

If there are exceptions to that, we haven't discovered them yet, so--and I think WHO is in agreement with us from their perspective as well.

The kinds of measures taken to identify super spreaders right now are retrospective. We can't tell, up front, who's going to be infectious and who isn't.

As I said, in the five individuals that were reported in today's MMWR, three of them had other medical conditions that increased the severity of their illness, but also might have confused SARS with some other medical condition and led to a delay in the implementation of infection control or isolation precautions.

So we do have to remind people that vigilance in the implementation of infection control, if you have any suspicion, it is important, even if there's an alternative diagnosis that might also come into play.

I'll take a question from the telephone please.

MODERATOR: Ladies and gentlemen, if you wish to ask a question, please press the star followed by the 1 on your touch-button phone. You may remove yourself from queue at any time by pressing the star followed by the 2. If you are using speaker phone, please pick up the handset before pressing the numbers. Once again, if you have a question, please press the star followed by the 1 at this time.

Our first question comes from the line of Seth Bornstein from Knight Ridder. Please go ahead with your question.

QUESTION: Yes, Dr. Gerberding. In terms of the Singapore, have you extrapolated that to some of the other hot spots in terms of super-spreaders? There have been reports of super-spreaders throughout Hong Kong and Beijing. Is there any relationship between the super-spreaders you've seen in MMWR report in Singapore and those in other places? And can you sort of give us a feeling on the other places on what percentage of the spread in the other places seems to be from super-spreaders.

DR. GERBERDING: We are aware that at least by observation there are reports of super-spreaders, and probably the first one that was recognized was the individual who was a resident in a hotel in Hong Kong for just a 24-hour period of time while ill, before that individual was admitted to the hospital. And that was the initial chain of transmission in that hotel that set up infection in travelers, who exported the infection to so many other parts of the world.

For me personally the first concern about a highly infectious patient arose in the American businessman who was a patient in Hanoi in mid-March, and the transmission to a large proportion of the health care personnel who took care of that patient. Of course, at that time it was not recognized to be an infectious disease, or certainly hadn't even coined the name, SARS, at the early part of that exposure situation.

So in those early cases, the super-spreading was primarily due to the fact that the disease was not recognized, and it was not recognized to be an infectious disease. That still remains probably the most likely explanation of what is a super-spreader, and that is that the person who simply has a large amount of contact with people when they are not using the appropriate containment or infection control precautions.

There's a diagram, and I know that those on the telephone can't see this, but in MMWR, there's a figure that shows how these five super-spreaders set up such large chains of transmission. And I think the picture is worth a thousand words in terms of really demonstrating graphically how a chain of transmission can cascade from a single point source.

And this is part of the reason why we continue to send the message as aggressively as we can here in this country, that we have to remain vigilant. Because if we were unfortunate enough to have someone with unrecognized SARS, or be admitted to a hospital, or to be present in an environment where they could expose many other people, we too could have a cascade of transmission established. We are certainly not immune to that.

And that is probably the most important lesson that we learned from the Singapore experience.

QUESTION: I guess--

DR. GERBERDING: Can I take another telephone question, please.

MODERATOR: Thank you. Our next question comes from the line of Jonathan Knight with Nature Magazine. Please go ahead.

QUESTION: Hi Dr. Gerberding. Thanks for having the press conference.

My question has to do with the CDC's patent application on the SARS coronavirus. And I'm wondering if the purpose is to ensure that SARS research can proceed unimpeded, as you suggested on Tuesday. I was wondering if you could describe how a SARS virus patent in private hands is not in the best interests of public health? Is it that DNA sequence patents throw up barriers to disease research in general? Or is it a special case in this case?

DR. GERBERDING: I think one concern is that depending on who held the patent, that it could potentially lock out competitors from being able to participate in the patent, or products of that patent. And so our decision was that first of all we would try to make as much information available in the public domain as we possibly could. And then secondly, if there is going to be a patent issued that we would apply for it, so that we could ensure that open access as we went forward.

We also have had more than 32 requests for either the virus or for segments of the virus to facilitate applications in the private sector, particularly for diagnostic tests, or for potentially antiviral development, and even vaccine development. We are very cautious about ensuring that people applying for products of the coronavirus are first of all able to have safe containment of the virus and appropriate bio-safety level facilities. But also that these are appropriate recipients of the virus who are trusted partners and will be responsible and safe handlers of the virus.

So far, we have completed biomedical license agreements with 17 of the 32 people who have applied and have made the products that have been requested available to those individuals. So, I'm just mentioning that because I think it's an example of our attempt to move this into the private sector and to do everything we can to promote vaccine development, and antiviral development, as well as diagnostic testing.

In addition to the private sector, of course we have made appropriate reagents and materials available to the NIH and to the NIH collaborating investigators, so that they can also engage in the science and development process.

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

QUESTION: Thank you, doctor.

A couple of questions. First of all, [Inaudible] department announcement of forced confinement being an option indicate a new level threat that you guys are seeing for super-spreaders entering this country potentially?

The other question is can you talk to the death rate, and the information that came out about the higher death rate in the elderly versus, you know the WHO report.

And thirdly, a New York Times article yesterday indicated some scar tissue in one of the patients. And is there any information on long-term effects that some patients who have recovered from SARS, what they might foresee as some long-term problems?

DR. GERBERDING: Thank you.

The quarantine process--and first of all let me again remind people of the vocabulary. Isolation is the procedure that applies to people who are infectious and ill with a potentially communicable disease. Quarantine is the procedure that applies to people who have been exposed to a disease, but are not currently sick or infected, potentially at risk for acquiring the disease and then transmitting it to others.

Our quarantine authority at the federal level, for example, at a border or a point of entry, includes both voluntary isolation and quarantine, as well as mandatory or required isolation and quarantine. Almost all isolation and quarantine activities that have happened in the last several decades have been entirely voluntary. But early in the course of SARS, we had a situation where an individual presented at a port of entry ill, and was under assessment for possible SARS. We did not have the authority to detain that person for assessment if they had decided to not comply with our voluntary requests.

And indeed that particular individual decided not to comply with the voluntary request. And so they left the airport and it took us a great deal of effort, and specifically a great deal of health authorities to track that person and identify their contacts. And then the state, who did have some authority, was able to intervene and be sure that there wasn't transmission.

But that taught us the lesson that SARS needed to be added to the list of conditions where, if absolutely necessary, we could impose a required isolation or quarantine act. That's why the President acted so quickly to execute the executive order for adding SARS to the list of quarantinable diseases.

We don't expect to have to use that authority very often. But what you read about in the New York Times was a clarification that if this act is considered, the CDC quarantine officers have the right to board planes, and assess passengers and so forth. But if a required detention is necessary, and needs to be enforced, the law enforcement component of the response resides in the customs inspectors.

And so the New York Times was reporting the fact that the customs inspectors, as they always have had the authority for detaining quarantines or isolated patients, was going to have the authority to do that for SARS.

So it really was nothing more than a clarification of an authority. And it was because of the reorganization of the Department of Homeland Security that there was some question about was that still applicable under the new organizational framework. And of course it was.

So we are already executing a memorandum of understanding with the Department of Homeland Security to make sure that we have engaged in a reciprocal arrangement to collaborate in those rare cases where such a step would ever be necessary.

Your second question was about the death rate, or the mortality rate from SARS. And I know there's been a great deal of interest in the fact that the death rate seems to be increasing in various countries, and that yesterday the WHO has reported an increase in the overall mortality rate from various methods of calculation that they've been using.

I'm not going to go into all of the specific details of why it isn't a straightforward process to simply know what the death rate is from a new infection disease. But there are a couple of reasons that I think we can all understand.

One is: As an epidemic is evolving, it takes time before we know whether or not a patient is going to recover, or a patient is going to die. So, for example, today we have 100 new cases of a new infectious disease. Today the death rate is zero. If tomorrow morning five people die, the death rate is 5 percent. And tomorrow afternoon if we have 100 new cases, then the death rate is 2.5 percent. So there is always a catching-up phenomenon as new patients come in to the denominator of the equation. It takes time before we know the people and the enumerator are either going to die, they're going to recover, or they're going to be in a period of time where we don't know their outcome.

So the simplest way to report a mortality rate is to simply add up all of the cases and add up all of the deaths and put that as a proportion. And for the reason I kind of just explained, because of the time lag in determining outcome, that's not really the most reliable method. We've been saying all along, "Expect the death rate to go up as we see the outcome or the conclusion of some of these sicker patients over time."

Another factor is that when you add up all of the cases and calculate the death rate, you're mixing apples and oranges together. We know that if your particular country has a lot of elderly people involved in your outbreak, the death rate is higher in elderly people, so your country is going to show a higher death rate. If your epidemic involves mainly health care workers, who are generally pretty healthy people, they will probably have a better survival from the exposure, and your death rate will appear lower.

So when we mix everything together, we've sort of got a conglomeration of a lot of different populations of people. The correct way for handing that is to stratify death by the factors of interest. For example, separately report what is the mortality rate for older people, what is the mortality rate for younger people, and so forth. And as we get more information in from all of the countries who are reporting cases, we'll be able to improve the precision of those estimates.

The last aspect of this really relates to the fact that some reports are including only a subset of the total number of patients. For example, the Lancet Report that was described earlier this week reported a higher death rate in Hong Kong than we had seen previously. But that report included patients who were admitted to the hospital with SARS.

Naturally, the people in the hospital are sicker than the people who are recovering or being cared for at home, so not surprisingly, the death rate may be higher if your sample includes a subset of the true picture.

So there are a lot of reasons why these numbers are changing. I think the important message, first of all, is that all deaths are important and matter to us as public health officials, and certainly to us as citizens of the global community who have empathy and concern for the affected people.

But also we have a lot to learn about the final outcome and the factors that do determine how well people survive this illness.

Most people do survive, I think that is still true, and we have not had any fatal cases in the United States and that's also a wonderful experience for us from the domestic picture; but we have had American citizens who have died from SARS in other countries and, you know, this is certainly not a situation where Americans are in any way immune.

So we will continue to provide an update and more precise mortality figures as we go forward.

SARS tissue in the lungs of SARS patients. The diseases in the patients who have pneumonia continue to unravel or we continue to learn more about it. We know that most patients with the severe pneumonia have a condition called acute respiratory distress syndrome.

If you looked at the lung tissue from someone with acute respiratory distress, or ARDS, what you would see under the microscope is just lung tissue that's basically destroyed. There's nothing left of it and you don't really notice anything specific. The pathologists call that DAD, or diffuse alveolar damage.

So that is really what the lungs of the autopsy specimens look like when the patients die.

When patients recover, they probably have a condition that was headed in that direction but, fortunately, their immune system was able to ward off the virus. But when you see how much damage can occur, it's not at all surprising that you would see some scar tissue or some residual damage from the condition in the less-severe form.

Whether or not that will ultimately improve or not remains to be seen, but in other infectious diseases, often the scar tissue does not completely resolve.

Patients may not have any residual clinical impact but on the microscope you can see the difference and there is of course the spectrum there as well.

The bottom line here is we need to do the long-term follow-up studies of the individuals who recover from the pneumonia to really understand what is their pulmonary function and how does it change or improve over time.

Let me take a telephone question, please.

MODERATOR: Thank you. Our next question comes from the line of Paul Shin from New York Daily News. Please go ahead with your question.

QUESTION: Thanks for taking my call, Dr. Gerberding.

Dr. Hughes mentioned, in early April, that the CDC is looking for a cohort of Americans who stayed at the Metropole Hotel, at the same time as an index patient. Have you begun the study? Have you been able to find a large enough sample and have you been able to derive an attack rate from this?

DR. GERBERDING: I'll let Dr. Hughes give you the updated perspective on that study. That is still ongoing.

Dr. Hughes.

DR. HUGHES: Hello. I'm Dr. James Hughes. I'm director of the National Center For Infectious Diseases here. Thank you for asking about that important ongoing special investigation. That's one of a number that we're involved in. We do have a list of the names and the addresses of over a hundred people who stayed at that hotel.

We are working with state and local public health partners around the country to follow up on those patients, to get information to determine whether or not they became ill and to get laboratory specimens.

So bear with us on that. That study's not completed yet. Thank you.

DR. GERBERDING: May I have a question from someone here in the room. No. Go to the telephone. Telephone question?

MODERATOR: Thank you. Our next question comes from the line of Elizabeth Kaledin from CBS News. Please go ahead with your question.

QUESTION: Hi, Dr. Gerberding. I'm just wondering. You know, you profiled travel histories of the patients in the United States. Is there anything else about those patients you can tell us in terms of their ethnic profiles? Sex, age, anything like that?

DR. GERBERDING: We had reported an earlier description of the race, ethnicity and age groups of the U.S. patients in conjunction with an MMWR that reported on individuals in several other countries as well, and we'll probably be publishing an update on that soon. So the data are available but we haven't kept it in an ongoing way, as a part of the regular MMWR report.

Periodically, we'll be updating it, and we are making plans also to publish some joint descriptions of a larger population of patients with some of our partners. So we will have it but we haven't made it continuously updated.

I'll take another telephone question.

MODERATOR: Our next question comes from the line of Jennifer Warner with WebMD. Please go ahead with your question.

QUESTION: Thank you, Dr. Gerberding. Could you comment on the report that's coming out tonight the Lancet about more evidence of a mutation of the SARS coronavirus. I understand it is common for them to mutate but is this rate of mutation anything that is concerning or surprising, and how will this impact the development of treatments and vaccines, possibly, for the SARS virus?

DR. GERBERDING: I'm not going to comment specifically on that article but as we have said, as soon as we recognized that this was probably an illness caused by a coronavirus, these viruses are expected to evolve over time. That is the nature of the particular type of positive trend in RNA virus that we're dealing with, and so the challenge is to determine whether or not there is a relationship between the evolution of the virus and the clinical presentation of the patient or the severity of illness among individuals, and that kind of work at this point is speculative.

We need to have a great deal more sequence information and a great deal more understanding of the other confounding factors before we could draw any conclusions about that.

I have a question here in the room.

QUESTION: Thank you, Dr. Gerberding. Betsy McKay from The Wall Street Journal. A question about the diagnostic test -- the laboratory tests that have been done so far on the samples that we've received, would you be able to tell us how many samples you have received here and what the turnaround time is roughly for the tests you have done.

One reason I'm asking is that for two weeks now there's only been six laboratory-confirmed tests. I'm wondering why that might be. Are there just not that many people with SARS, or is there some sort of backlog with the tests?

DR. GERBERDING: The problem is not a problem of backlog. The problem is that we aren't reporting the status of the test result until the patient's 21st day or greater sample has come in, and so we have to get the samples from the patient, get them here to CDC and then pair them up with their first sample. So this takes time, and the biggest lag is generally in getting the samples from the individuals, especially since most of these people are completely well now and aren't particularly eager to come back in and have their blood drawn, and so there is always some time lag in that regard.

We also are testing not just the U.S. patients. We are participating in laboratory evaluation of international samples. So we are doing a great deal of testing in our laboratories. At the same time that we're testing the samples from the various collaborating parts of the world, we are evaluating our tests and calibrating our tests and optimizing our test methodology.

So, you know, it isn't just something we could pick up off the shelf and immediately optimize. There's been a great deal of quality control work going on.

For the PCR test, the next test that we'll be making available, in order to have a positive control for that test since it specifically looks for pieces of the virus, genetic material, we have to create positive controls.

We don't want to send virus out to laboratories for positive control, so we're sending a genetically-engineered piece of the virus that we know has the target sequence contained in it, and we have to manufacture that, and so that is a process that obviously takes some time, and when we're getting ready to scale up for the kind of volume that we're dealing with.

So test development is a work in progress. It's not an event, it's a process, and I know it seems like it's taking a while here, but from our frame of reference, given how long it typically has taken to develop diagnostic tests, I still think this has got to be the fastest test development process that I'm aware of.

I don't know, Jim, if you've seen anything go faster than this; but it would be hard to imagine. So we're pretty pleased with the progress that's being made and I think our laboratory scientists have really maintained their high standards of excellence. But it is still very significant to us that we can make the first test available to the States in such a rapid timeframe.

Do I have another question from the telephone?

MODERATOR: Yes. Our next question comes from the line of John Lauerman with Bloomberg News. Please go ahead with your question.

QUESTION: First, I was wondering if you'd just reiterate the WHO numbers because I don't see them up on the site yet and I would like to get them.

And second, I wanted to also ask about the rate of mutation. The editorial, also in the Lancet, that says that if the virus is mutating slowly, it's a double-edged sword because it's less likely to become resistant to drugs but it's also less likely to mutate into a benign infection.

I was wondering if you'd comment on that.

DR. GERBERDING: Yes, the WHO is reporting 6,838 patients other than those in the U.S. and that patient population has experienced so far 495 deaths, and without counting the U.S., involving two countries.

The U.S. is reporting 63 probably cases today and 265 suspect cases.

The rate of mutation of course remains to be determined. Darwinian biologists or an evolutionary biologist would expect that any living organism evolves and changes over time, and that there is a trade-off between the virulence of the organism and the transmissibility of the organism.

Organisms do not have a vested interest in having high mortality rates because that means that they end up not being able to be transmitted to anyone.

On the other hand, organisms don't necessarily benefit from creating conditions where the person doesn't get sick enough to cough or sneeze and transfer the virus from one person to another.

So as nature selects, for any pathogen there are a variety of balancing factors that come into play, and I think it's far too early to speculate on whether the rate of change here will result in a benign virus or whether or not the major problem will be drug resistance.

I think our experience with pathogens so far has been that what we see clinically and epidemiologically tends to favor evolution to drug resistance, and certainly not an attenuation of pathogenicity over time. So we are not optimistic that evolution will be kind to us in this case.

Do I have a question here?

QUESTION: Dr. Gerberding, just a point of clarification. We have gotten reports that there were 503 total deaths worldwide from SARS, from the WHO. Now those are different than the numbers you've just said. Is there a--do you know where that discrepancy comes from?

DR. GERBERDING: Do you know the discrepancy?

DR. HUGHES: We appreciate your ongoing interest in these numbers. We did not have access to today's numbers when we came down here. The WHO had not posted them as of shortly before 2:00 o'clock. I think they must have by now. So the numbers that Dr. Gerberding gave you were actually WHO's numbers from yesterday and the U.S. numbers were from today.

DR. GERBERDING: Thank you. Time lag. A question from the telephone, please.

MODERATOR: Thank you. Our next question comes from the line of Anita Manning with USA Today. Please go ahead with your question.

QUESTION: Hi. Thanks very much. Dr. Gerberding, why has it taken the U.S. so long to report the source of the probable cases here in the U.S.?, and what I mean by "sources," what countries they came from. Why is it taking so long to report that to WHO?

Has there been some resistance to give that information?

DR. GERBERDING: I don't think there's been any resistance here. One of the things that we're really struggling with is the differences in case definitions from various countries, both in the probable category as in the suspect category, and you know in the U.S., we made this very conscious decision to cast the widest possible net and capture as many people as we could who could possibly have SARS, so that we were implementing the infection control precautions.

The other issue for us is that SARS is not a disease that is required to be reported to CDC, so our whole ability to obtain information about SARS patients depends on the collaboration that we have with state and local health authorities whose interest is certainly in protecting the public's health, but, in many cases, their interest is also in protecting the confidentiality of individuals.

Some of our case patients come from very small communities and if we provide information that details their explicit travel history or the location of their flights, and so on and so forth, it's basically identifying information.

So we are always balancing the concern we have for individual privacy with the important public health information that WHO obviously needs to have to make sure that the entire international community is made aware of cases.

As you can see from the list of individuals that we presented today in the MMWR, there's really very little to be learned from our countries of origin, since these are the places the WHO is already highly aware of. If we had a case of SARS in an unusual location or an exceptional situation, we would certainly alert the global community about any concern that we had that was of public health importance.

So for us it's a balancing act and now that our numbers are a little higher, the information becomes less identifying, and we have the confidence from our state and local partners that this isn't a reasonable time to begin to make this kind of information more public.

So part of our issue is confidentiality and part of it is related to that, is the relatively small numbers of patients that we've had here.

Do I have another question from the telephone?

MODERATOR: Yes. Our next question comes from the line of Maggie Fox with Reuters News. Please go ahead with your question.

QUESTION: Hi. Thanks very much. I wanted to ask about the whole question of immune system versus actual viral damage to the lungs.

I know you don't want to comment on this unpublished Lancet report or the embargoed Lancet report, but there's a suggestion that immune response is responsible for the damage, and in the meantime there's lots of companies who are "making hay" off the fact that they have immune-affecting drugs.

And I have a second question which is about spitting. Nobody's raised this issue but I know there have been campaigns in China in the past to stop people from spitting, and is that a potential mechanism for transmitting SARS?

DR. GERBERDING: The pathogenesis of the SARS pneumonia is still incompletely defined. The best hypothesis is that there's a combination of viral infection, direct infection of the virus in the lung tissue, and then a phase of immunologic response.

That may then be followed by that third and highly fatal phase of the acute respiratory distress syndrome which is really the end stage of a profound inflammation in the lungs, that we see in a minority of these patients.

To predict at this point in time whether or not an anti-viral treatment or an anti-immune treatment or an immune globulin treatment is appropriate intervention is at best, at this point in time, a very speculative, if not risky endeavor.

We need to evaluate these therapies in animal models and we need to more carefully define what really is the mechanism of infection and alveolar damage.

The NIH has already developed some protocols at their clinical centers so they can get very detailed evaluation of the immunology and pathogenesis of the illness.

WE are also working with our collaborators in Hong Kong. I spoke with one of the health officials in Hong Kong, the other night, to try to understand what they were doing to assess treatments and interventions, and I think this is far too early in the game for us to put patients at risk with speculative therapy.

So the first step from the CDC perspective is let's get the science out in front of the clinical decision making and if we have hints or leads for what looks to be promising, that's the appropriate point to initiate an investigative study.

I think you had a second question. Oh, it was about spitting.

I have not heard any evidence to suggest that spitting has been a source of transmission but spitting would fall into the category of droplet dissemination and so I think we would be concerned that if someone was spitting and the spit came in contact with someone else's mucous membranes, then that would not be a desirable outcome.

So while we have not issued any specific guidance against spitting at the CDC, I think it's a common sense personal hygiene measure and we would generically discourage it.

Any other question from someone in the room? I'll take one last question from a reporter on the telephone.

MODERATOR: Our last question comes from the line of Barbara Carroll with NewsMax Media. Please go ahead.

QUESTION: Thank you, Dr. Gerberding. Can you tell us more about the life of the virus on surfaces. We've been sort of reading a little bit of this and that. Can you give us something more to go on?

DR. GERBERDING: The life of the virus on surfaces is a subject of interest for two reasons.

One, it pertains to us defining what is the best way for disinfection of surfaces for decontamination procedures and hygiene procedures, but it also pertains to potential modes of transmission through contaminated objects, et cetera.

The science of the experiments looking at longevity in the environment on surfaces is a very difficult science to draw conclusions from because the methods are extremely variable.

However, the experiments that have been done so far really indicate that you certainly can recover coronaviruses from surfaces for at least 24 hours after they've been placed there.

We knew that from the beginning. That's why we recommended the importance of hand hygiene and contact precautions in health care settings.

But a confusing issue for many people is that finding a virus on a surface does not necessarily mean that surface has anything at all to do with transmitting the virus from one person to another, and if you think back to the early days of HIV infection, we had a lot of data coming out indicating that HIV could survive on tabletops for prolonged periods of time, but in fact tabletops were not a mode of transmitting HIV from one person to another.

So we need to distinguish between the theoretical observations from what we understand about how the diseases has actually been transmitted.

One other point about this. These experiments typically are done by taking very high concentrations of virus and spiking that material into a solution, and when you start out with a very large amount of virus, and certainly more than we would probably expect to see in a patient, then it's even more likely that we're going to be able to recover that virus from that same surface at later points in time.

So there is a lot of work to b done here in terms of the role of the environment and the role of objects in transmission.

For now our guidance holds. Hand hygiene, hand washing, and for health care workers airborne droplet and contact precautions in the health care environment.

I wanted to just end today with the context that we are always vigilant about the importance of early detection and recognition of SARS patients, but we also want to have the right balance between the minimization of the disease and minimization of the inconvenience and harm to individuals and events in our society. We are taking, I think, the appropriate measures at this point in time in this country to protect us against SARS.

Our system is very highly engaged in doing this but we are also seeing reports and concerns about restriction of people coming into this country for various reasons, whether it's for school events or for business events, and so on and so forth, and I wanted to be clear that the CDC recommendation on this issue is the same as the WHO recommendation on this issue and that is that we are basing our recommendations on science.

We are taking what we believe to be the appropriate public health measures through our health alerting process, plus all the things I described that are going on in the countries of origin, and we currently are not recommending any changes in or any advice to people to avoid coming into the country if they've been in areas where SARS is being transmitted.

We are alerting those individuals of the importance of seeking medical attention if they acquire any symptoms in the next ten days, and today I just completed a phone conversation with the dean of the school of public health and we will be developing some specific guidance that will pertain to our academic communities and potentially similar communities where large groups of people are aggregating for events like graduation.

So please stay tuned to the CDC Web site and as we have more information and guidance for you, we will be making it available in that form as we go forward.

Thank you.

MODERATOR: Ladies and gentlemen, that does conclude today's conference for today. Thank you for your participation and for using AT&T Executive Teleconference. You may now disconnect.

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