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CDC Telebriefing Transcript

Update on West Nile Virus Investigation

September 19, 2002

CDC MODERATOR: Thank you very much for joining us. This is Lisa Swenarski, director of media relations at the CDC.

Today we have three speakers on the call in addition to two people who are also available for questions. Let me introduce them. Dr. Lyle Petersen, CDC West Nile virus expert; Dr. Jesse Goodman, deputy director, FDA's Center for Biologics Evaluation and Research. We also have Dr. Jim Sejvar, medical epidemiologist with CDC, who will be speaking about MMWR article, "Acute Flaccid Paralysis Syndrome Associated with West Nile Virus Infection."

In addition, we have two people available for questions: Dr. Ed Thompson, state health officer, Mississippi Department of Health; and Remy Aronoff, deputy director of HRSA's Office of Special Programs. Thank you.

We will turn it over to Dr. Lyle Petersen for his opening statement.

DR. PETERSEN: Thank you. As of yesterday, the number of West Nile virus cases reported to CDC has reached 1,641, with 80 deaths. Note that in the MMWR article this week, the article states that there were 72 deaths. The correct number is actually 80. All of these counts will be updated later today.

With the addition of North Carolina reporting its first case, 36 states and the District of Columbia have reported human cases of West Nile virus in 2002. By far the majority of infections have been the result of mosquito bites carrying the West Nile virus. However, in a small number of cases, it appears transmission occurred by way of transplanted organs and blood transfusions, either together or separately.

We are reporting today two investigations of recipients of organs and blood products, four investigations of transfusions recipients, and one investigation of a West Nile virus sero-negative person with fever and encephalopathy, who received a potentially contaminated unit of blood.

One investigation in Georgia demonstrates that West Nile virus transmission can occur via organ transplantation. In another investigation in Mississippi, the isolation of live West Nile virus from a blood product indicates that the virus can survive in some blood components, and probably can be transmitted by transfusion.

CDC continues its investigation of these cases and is actively seeking information on any possible other cases that may follow similar patterns.

CDC MODERATOR: Thank you. Dr. Goodman?

DR. GOODMAN: Thank you. Good afternoon. You just heard Dr. Petersen's update on some of the ongoing investigations. And I think you've heard that, at this time, the results are not totally conclusive with respect to blood-borne transmission through transfusion.

However, we really believe that, given the results of these recent investigations, it is most prudent to assume that blood-borne transmission likely has occurred, at least in some of these instances.

While critical studies continue and others are initiated to assess both these cases and the true risk of West Nile virus in different donor populations, several actions are being taken by us and our partners.

First, as Lyle has mentioned in the past, reporting of cases of West Nile virus in the setting of recent transfusion or transplantation is being encouraged, and any indade [ph] blood products that could pose a risk or potential risk to others have been and will continue to be withdrawn.

Second, in one of the cases--probably the case with the strongest evidence suggesting transfusion transmission--there was a history of an illness developing soon after the donor donated blood. Given this, FDA is working with blood banks and will provide guidance on the solicitation of information on illnesses occurring after blood donation and the appropriate actions to investigate and act on such information, including possible product withdrawal--again, to protect others.

Third, FDA really believes that since this transmission by transfusion is likely, it is likely also that we will need to move rapidly toward testing of donor blood, at least in areas and during time periods when West Nile virus transmission actively occurs. It's important to recognize that while no validated test for this purposes is currently available, while screening of large numbers of samples is something that we can't just implement overnight, we are urgently interacting with and meeting with partners in the blood-banking community, the diagnostic testing industry, along with laboratories such as CDC's and other public health labs who have tests that could potentially be adapted to the blood screening setting.

What we're trying to do here is to jump-start and facilitate this process so that we can get a test available as soon as possible to screen blood, if that is needed. In doing this, FDA can utilize its regulatory authority to allow use and evaluation of a screening test in a public health setting even before it meets those requirements for licensure.

Finally, there is another technology, called pathogen inactivation, which involves treatment of blood and blood products to kill potential infecting agents. This is a promising tool which FDA recently held a workshop on, that could potentially be used in our armamentarium as we address West Nile virus threat. FDA is and has been working with manufacturers to evaluate the potential effectiveness and safety of this strategy, and will continue to discuss this specifically with respect to West Nile virus.

So I think that it is important to say that while the investigations are ongoing, we believe there's sufficient evidence, when you put it all together, to say that there is likely a risk, that it is likely that at least some of the reported cases may be related to transmission by blood and, certainly in the one case, transmission through organ transplantation.

It is important, as always, to keep a risk, even a poorly understood risk, in perspective. As we have said, there are approximately 4.5 million people in the United States who receive blood products each year, and both blood and blood products and organ transplantation are often life-saving, or life-enhancing. For people who need a transfusion or transplant, our current knowledge suggests that the potential benefits will outweigh the risks, including the risk of West Nile virus infection.

However, we also think--and we have striven with our partners to share as much information as we have available, and we think people do need to be aware of this potential risk and should discuss it and their medical treatment with their physicians, including potential alternatives.

The FDA and its partners will continue to do everything possible to determine the degree of this risk and will find and take all available steps to reduce it. And we will continue to update the public as new information becomes available.

Finally, it's important to say that blood donation is safe. And the FDA and all of its Public Health Service partners encourage donation of blood by well individuals. Thanks.

CDC MODERATOR: Thank you, Dr. Goodman.

And now, Dr. Jim Sejvar will speak on his article, "Acute Flaccid Paralysis Syndrome Associated with West Nile Virus Infection."

DR. SEJVAR: Thank you. My name is Dr. Jim Sejvar, and I'm a medical epidemiologist for the National Center for Infectious Diseases.

I'd like to summarize for you the article published in today's MMWR, entitled "Acute Flaccid Paralysis Syndrome Associated with West Nile Virus Infection, Mississippi and Louisiana, July and August 2002."

Many patients with West Nile virus infection who develop acute weakness are diagnosed with a condition called Guillain-Barre syndrome, and receive treatments including intravenous immune globulin and plasmapheresis, which could have adverse side effects. Our study suggests that many of these people may in fact have an illness similar to acute polio, which is not helped by these treatments. And if they are receiving treatment for Guillain-Barre syndrome, it could possibly do more harm than good.

In areas where West Nile virus transmission is occurring, patients who develop weakness that is asymmetric, does not involve sensory changes, and have lots of white blood cells in there cerebrospinal fluid may have a poliomyelitis-like syndrome. Physicians need to consider and test for West Nile virus and also need to strongly consider performing tests to differentiate Guillain-Barre syndrome from the other causes of weakness before initiating therapy.

CDC MODERATOR: Thank you. And now we're ready for questions. First question, please.

AT&T MODERATOR: Seth Borenstein, with Knight-Ridder.

QUESTION: Yes. Dr. Goodman, when you're talking about speeding up both the pathogen inactivation and the diagnostic testing systems, has there actually been a decision to--how close are you to a decision to say go ahead with the use of tests and use of pathogen inactivation? Are we talking weeks on a decision, weeks on use of a test? If you could give me some kind of time scale here.

DR. GOODMAN: Well, I'll try my best. It's a difficult and important question.

First of all, we want to act at a point here, even though we have what is fairly preliminary information. But we believe that to wait until we have proof on additional cases, to wait for data from population-based studies before moving blood-screening testing forward would be a mistake. So while I would say that at this moment we need more data to make a decision whether such screening would need to be initiated and where, we think, based on the evidence we've seen so far, that it is likely that it will be needed. And therefore, we are proceeding as if it will be. Of course, we will assess that as additional evidence comes in.

In terms of when it is available or when it could be available, I think it is important to point out, as I mentioned, that it's not something one can take overnight from a small-scale research or public health laboratory setting, where it's used for the diagnosis of disease, to a very large-scale distributed setting where it is used to screen tens of thousands or hundreds of thousands of units of blood.

So we do not have an answer right now as to exactly how long it will take, but we want it to take as little time as possible.

On the pathogen inactivation question, that--I'd say there the technologies are in existence. I think, again, as we evaluate the continuing nature of information about West Nile transmission by blood and the data that we're encouraging from the manufacturers of these technologies to show us how effective they could be for this, we will work with them to determine what the appropriate usages of those would be.

So those discussions are both ongoing. FDA is planning a number of meetings to consider these issues in the near future.

CDC MODERATOR: Thank you. Next question, please.

AT&T MODERATOR: Adam Marcus, HealthScout.

QUESTION: I have this question for Dr. Sejvar. I'm wondering if there's any information on how long the polio-like syndrome lasts.

DR. SEJVAR: At this point, we really can't say accurately. What I can say is that the cases that we have been observing have been ill for about--between a month and a half and two months, and they have shown very little improvement. It's something that we're going to have to continue to follow, however.

CDC MODERATOR: Next question, please.

AT&T MODERATOR: Marilyn Marccione, Milwaukee Journal.

QUESTION: A follow-up to Jim on the same issue. Can you talk at all about the pattern with other flaviviruses that produce acute flaccid paralysis, how long that has been known to last; and also other sporadic reports of this with West Nile?

DR. SEJVAR: An acute flaccid paralysis very similar to what we have been observing has been observed with other flaviviruses, including Japanese encephalitis. And in fact, there have been case reports in the past of West Nile virus causing this type of syndrome. Unfortunately, I don't have information as to how long this paralysis lasts, even in these cases.

CDC MODERATOR: Thank you. Next question?

AT&T MODERATOR: A.J. Hostetler, Richmond Times.

QUESTION: Hi, good morning--or rather, good afternoon. I'd like to follow up on some of the questions regarding the screening. Dr. Goodman, will this follow the pattern that we saw with AIDS and hepatitis on nucleic acid testing? Would the FDA want a large pooling sample at first and the moving toward testing individual donations?

DR. GOODMAN: Well, this is the subject of discussions that are ongoing both internally and that we're going to engage our partners with. I think there is a lot that we've learned from the very effective initiation of nucleic acid testing for those diseases, that we'd like to apply to this to, hopefully, make it go faster.

One of the issues, which I think you may be interested in and hinting at, is that it does appear that the levels of this virus in the blood are far lower than those for those other disease that are tested, and therefore the demands for this test to be sensitive are higher. And these are the issues that, as we assess the technologies and try to work with the various parties to get them translated into practice, we're going to need to consider. And the pooling issue, do you test multiple samples together, is very directly related to that, because obviously, as you mix multiple samples together, to some degree your sensitivity for any individual sample within there can decrease.

So this is precisely what we're working to determine right now, which is the most appropriate strategy to get us there quickly, but quickly in a way that works and protects the public.

CDC MODERATOR: Thank you. Next question, please.

AT&T OPERATOR: Thank you. Our next question comes from John Pope with the New Orleans Times-Picayune. Please go ahead.

QUESTION: Thank you. I have two small questions--one on the acute flaccid paralysis. Is there any way for a doctor to tell at the outset if someone who may have West Nile, whether that person is likely to go into acute flaccid paralysis?

DR. SEJVAR: At this point--are you asking--can you state the question again?

QUESTION: Sure. I'm just wondering if this condition that you've spotted in the state where I work is something that might be tied--if you have enough cases yet to be able to tell what type of person who comes down with the West Nile infection might be more likely to develop acute flaccid paralysis. Is there some way that a clinician could know from the get-go?

DR. SEJVAR: At this point we have not identified any particular risk factors which would indicate the development of this condition. It does seem to occur rather quickly after the onset of illness, however.

QUESTION: A tiny question. It's my understanding now that as far as transfusion- and transplantation-related cases, that the test now for the virus is actually a test for the antibody to the virus. How--assuming that's true, how long--let's say a person is bitten by a mosquito and then goes in--and feels fine and donates blood, is there a period during which this infected person could well be passing on infected blood without knowing it before the antibody test could pick it up?

DR. GOODMAN : Absolutely, and that's the key [inaudible] here. We believe and CDC scientists also believe that the time when the virus is in the blood is very early after the mosquito bite and at a time before antibody even develops, so that the current antibody tests, at least, are unlikely to identify all individuals who might be infected [inaudible] just wait for that noise to subside.

So what we believe is the more promising technique, unless one of the parties we're bringing in can show us a highly sensitive early kind of antibody detection assay--which we would be doubtful of based on what we know about this disease, but we believe that the most likely way to rule out a donor carrying infectious virus would be to detect the nucleic acid, the virus itself in a sample. That presents a bit more of a challenge on--you know, because these assays are more difficult to do, more technically demanding. On the other hand, as mentioned, this is a route that has been taken to tremendously improve the safety of our blood supply for other virus pathogens.


Next question, please?

AT&T OPERATOR: Thank you. Our next question comes from Miriam Felco (ph) with CNN. Please go ahead.

QUESTION: Hi. I have a couple of questions. I want to make sure that the blood donation cases, I'm reading them right. We know four people got West Nile virus from the organ donor in Georgia. We know a different person may have gotten the virus from a different organ donor. And then we also know that one person got West Nile virus after receiving infected blood--that would be the 24-year-old woman--and that there are six more cases under investigation. Do I have that right?

DR. PETERSEN: Yeah. There--right now, just to recap what we have presented here, there is--let me make sure that I have--give you the facts right.

There are two cases that involve potential organ transmission. The first case is the one in Georgia, which we've previously reported on in which there's four West Nile virus-positive recipients. There's a second case involving a potential organ transplantation. However, that person has also received multiple blood transfusion in--transfusions in addition to the organ. So we're still trying to work on that case to figure out whether it's organ--it's the organ, it's the transfusions, or it's a mosquito bite.

There are four other investigations that involve potential blood transfusion, one of which is this 24-year-old. In addition, there is a rather unusual situation where we've identified a donor who is Taq Man or PCR positive, indicating the donor had evidence of viral genetic material in the blood at the time of donation that was transfused into a person who developed encephalitis two days later.

So far the testing of that person has not revealed West Nile virus, so we don't know the cause of that person's encephalitis, nor do we know that the encephalitis was related to the transfusion.

QUESTION: So the reason why I mentioned six cases was because that one organ donor might have gotten it from the blood. So you've got--I think I've got it right.

Now, regarding the blood testing, I've got two little questions. The blood testing--right now you're saying that the nucleic acid test would be much better but you don't have that yet. Would it make sense to use what you do have, the antibody test, until you have a better test to see--to do whatever you can to make sure that the blood that's being given to people is not--does not have the West Nile Virus? And then for Dr. Petersen, a few weeks ago you had said the peak for the West Nile virus was expected to be end of August, beginning of September. From what I'm seeing watching these case reports, it doesn't seem like we've peaked yet, but I would like you to tell me. Have we peaked yet? Do you think we have? Or is there still a lot more time we're looking at having this disease--or people infected with this disease.

CDC MODERATOR: Dr. Goodman, do you want to take the first question?

DR. GOODMAN: Yes. That's a good question, and it's certainly on the table, and we are going to discuss that with the various diagnostics experts in our meeting.

The one point I would make is that at least the current experience of laboratories that work actively in investigating West Nile disease--and Lyle may wish to comment. But the current experience is that when individuals have antibody, at that time it is very difficult to detect virus in their blood. So we would be skeptical that at least the antibody assays that have been widely available would identify and protect the public from a variety of potential transmissions.

Now, having said that, one of the things that we are doing is--in the CDC laboratory and potentially others, in cases--and, of course, right now there is only the one that is--where the evidence is very strong, but the others are under investigation. But in cases like that, we can look at those pre-donation blood samples and see if, in addition to finding virus by nucleic acid testing, there is any evidence of antibody production at that time. And maybe Lyle would like to comment on the results of that in that one individual.

DR. PETERSEN: Right. The best study case we have--there's actually two cases right now that are noteworthy with this regard. The first case is the case of the Georgia organ donor. At the time of--that the organs were taken, there was evidence of virus in the blood in that organ donor. However, the antibody tests were negative.

In the investigation of--regarding the young woman in Mississippi, the donor--those donors were also antibody-negative but showed evidence of virus in their blood. So we think that the antibody test is not going to be very sensitive for picking up early infection, as Dr. Goodman has mentioned.

There's a couple other caveats here, too, and that is that what we're measuring is IgM antibody in these tests which detect acute infection. However, the IgM antibody test may remain positive for a long period of time, perhaps more than a year or two. The fact that there are many people in the U.S. that have been infected this year, perhaps up to a couple hundred thousand, would suggest that many people will have this antibody in their blood but be perfectly safe as blood donors. In fact, people with the antibody in their blood may be the safest donors with respect to this since these people have already been infected and have recovered, for the most part, and, therefore, are immune from acute infection.

CDC MODERATOR: Dr. Petersen, do you want to answer her second question on the peak of--

DR. PETERSEN: Yes. When we talk about the statistics, you have to keep in mind that there is a slight delay between the time of onset of the symptoms and the time they're reported and show up in the statistics. And that is because sometimes it takes the patient several days to go to the doctor, or even weeks to go to the doctor. The doctor has to get the test. The test has to be run and then the case has to be reported. So there's a slight delay. So even though the infection may have peaked in certain parts of the country, more cases will still continue to be reported.

Now, the best evidence we have right now suggests that in the Southern United States the epidemic has probably peaked and is on the down side. However, a significant number of infections are still occurring, and people have to be vigilant to avoid mosquito bites.

In the Northern United States, it's still too early to determine whether the epidemic has, in fact, peaked. We would expect based on historical data, looking back at the St. Louis encephalitis outbreaks in the past, that the epidemic will peak sometime in mid-September in the North Central United States.


Next question, please?

AT&T OPERATOR: [inaudible] comes from the line of Anita Manning, USA Today. Please go ahead.

QUESTION: Hi. Thank you very much. I have questions about the AST findings, and one of them is: What are anterior horn cells? And the other is about--you had mentioned the treatment for GBS, mistaken treatment is harmful, and yet you've also said that it--that these cases occur really early. So I don't know how a doctor can make the determination. Maybe you can explain that to me.

DR. PETERSEN: Yes. Anterior horn cells are the--the nerve cells that most directly allow the muscles to move. They're known as the lower motor neurons. The motor--they're the nerve cells in the spinal cord that help with movement.

Now, the second part of your question was what?

QUESTION: It wasn't very well stated. I'm sorry. I guess--you had mentioned that the symptoms of paralysis occur shortly after infection, and also that treatment--if doctors see this and treat people for Guillain-Barre syndrome, that that could be more harm--harmful. And so I'm wondering, that sort of places doctors in a terrible position because they might see a patient with paralysis and how are they supposed to determine very quickly whether it's West Nile or Guillain-Barre. Is there some way of doing that?

DR. PETERSEN: What we're saying is that, in places where there's a high rate of transmission, that people who are presenting with acute weakness, that the idea that it may be due to West Nile virus needs to be taken into consideration. And before initiating treatment, the proper tests to differentiate Guillain-Barre syndrome from a poliomyelitis-like illness need to be done. And as far as the treatment, the treatment is not necessarily harmful per se, but it carries with it significant risk factors. And if a person does not need that treatment, it could potentially do more harm than good.

QUESTION: I see. Thank you very much.


Next question, please?

AT&T OPERATOR: Marian McKenna, Atlanta Journal Constitution. Please go ahead.

QUESTION: Hi. Thanks very much for doing this. I have one question for Dr. Petersen and one for Dr. Goodman, Dr. Petersen first.

Could you be a little--could you help me sort out--could you be a bit more clear? The various investigations you are talking about today, seven different investigations, the first of them involving the organ donor and the four recipients, could you associate that with the states that you discussed last week in which there were cases? Last week, you had a potential total of five cases via transfusion if you included the organ donor and the woman in Mississippi, and now you have, it looks like, seven.

DR. PETERSEN: Right. There's a case in Georgia. In this MMWR it's listed as Investigation 1. There is the case we've been talking about in Mississippi, which in the MMWR article is listed as Investigation 3. The other investigations are ongoing, including Louisiana, Mississippi, and Michigan--and North Dakota, excuse me. Those four states. And I do not want to link specific investigations to specific states at this time for these other investigations because at least one of these states has a small number of West Nile virus cases and would like to try and preserve confidentiality of that person.

QUESTION: Last week, you said that two of the cases were in Mississippi. Can you say which other state has two cases or if Mississippi has three?

DR. PETERSEN: There are two--

QUESTION: Can you give us a total--

DR. PETERSEN: There are two investigations in Louisiana and two in Mississippi.


Dr. Goodman, given that the test for nucleic acid for West Nile is going to be a while in coming, though you hope it won't be a long while, and given, as Dr. Petersen explained, that the antibody tests may not be useful except for identifying people who would be good donors as opposed to ruling out donors, do you have any plans at this point to start promoting some of the alternatives that were talked about when HIV first became identified as a problem in the blood supply such as autologous donation or blood-sparing technologies in surgery or postponing elective surgery?

DR. GOODMAN: Good and appropriate question. At this point, you know, we're in a very dynamic setting where we believe there is a risk and we're acting on it, but we, in all honesty, do not have the information yet to define how great that risk is. So I think that for individuals--we want to make blood recipients and organ recipients fully knowledgeable about what we know about the risks and with this conference they pretty much are.

But I think that for individuals, if they are concerned about this risk and if they are in a situation where their surgical procedure or whatever is highly elective, they should discuss with their physician their potential alternative and what their benefits and potential problems might be. And certainly the ones you mentioned--blood-sparing forms of surgery, blood-recovering surgery, where it is possible, storage of sufficient autologous blood to cover an elective surgical procedure--are very medically appropriate steps that one could take if one was concerned about things at this time when the risk is uncertain.

Similarly, the issue of postponing elective surgery. Again, I think that's a very individual decision now because of the fundamentally uncertain nature of our information about the degree of risk. So I think those are all valid possibilities you've brought up. I think there's too little information right now to make a general recommendation to all individuals. But we are supportive of individuals being aware of this potential risk, choosing how they wish to approach it.


Next question, please?

AT&T OPERATOR: Denise Grady, New York Times. Please go ahead.

QUESTION: Thank you. Is it known how long the virus remains in the blood? And then I'd like to ask a follow-up, please.

DR. PETERSEN: We do not know precisely how long the virus remains in blood. However, there were a number of studies done back in the 1950s where West Nile virus was injected into people for treatment of cancer, so these were not normal people that the virus was injected into. At that point it was thought that viruses causing fever could be potential cancer therapies, and that's why this was done.

Evidence to date suggests that the virus in those patients--excuse me, the data from that study indicated the virus amongst patients with mild cancers was on the order of five days. But, again, we do not know how long the virus will remain in the blood in healthy people, but it's going to be on the order of a few days.

QUESTION: Okay. Thank you.

DR. GOODMAN: I was just going to add something to that, just to mention some information that CDC has from studies, both this year and in previous years, that helps reassure us somewhat about that is the fact that, as I had mentioned earlier, when patients do have symptoms of West Nile virus at a time that they have antibody, it's been extraordinarily difficult using some of the same technologies to find virus in their blood. So these things taken together are--suggest a relatively short [inaudible] of virus in the blood.

Lyle, is that a good reflection of those studies?

DR. PETERSEN: That is correct.

CDC MODERATOR: Did you have a follow-up question?

QUESTION: Yes. My other question was generally regarding the spread, the expansion of the number of cases and the number of deaths. Is this--is there anything surprising or unexpected here, particularly with the number of deaths and the rate of the increase?

DR. PETERSEN: Well, I think any epidemic of this size is a--is surprising, but it's not totally unexpected. Going back to 1975, there was an epidemic of St. Louis encephalitis virus, which is a very closely related virus to the West Nile virus, that caused nearly 2,000 cases of meningo-encephalitis. And, in fact, this outbreak is behaving much like that 1975 St. Louis encephalitis outbreak. In fact, even some of the same neighborhoods affected in 1975 are being affected in this year with the West Nile virus. So it's not totally unexpected that this could potentially happen, and, in fact, we have been preparing for this eventuality in the last several years by setting up laboratory capacity, setting up surveillance, helping to promote prevention programs to prepare for this.


Next question, please?

AT&T OPERATOR: Joan Harris, ABC News Radio. Please go ahead. Joan Harris, your line is open.

[No response.]

AT&T OPERATOR: We'll move on. Tom Watkins, CNN. Please go ahead.

QUESTION: Can you give some more details about this, what appears to be a new syndrome? First off, is it fair to call it a new syndrome or is it just a suspected new syndrome? Secondly, how sick are these people? Can they move their arms and legs, or are they wholly paralyzed? And is their ability to breathe also depressed? Are they on ventilators? And is there any treatment that you're giving? Then, finally, what are the tests that doctors need to distinguish Guillain-Barre from whatever this new or potentially new syndrome is?

DR. PETERSEN: Okay. First I'd like to state very clearly that this is not a new syndrome. Again, flaccid paralysis has long been recognized to be a complication or an association with West Nile virus infection. What we're suggesting is that the actual cause of the weakness is something other than what has traditionally been--traditionally been suggested.

With regards to appropriate testing, for the most part physicians would want to consider first of all a lumbar puncture to look for evidence of increased white cells in the cerebrospinal fluid. They would also want to consider doing what's called an electromyography, EMG, and nerve conduction studies, which can help differentiate processes that affect the peripheral nerves from processes that affect the spinal cord. And then finally they might--they would want to consider doing imaging of the spine, again, to look for evidences of abnormalities in the spinal cord.

And at this point there is no therapy specifically for this condition. Now, again, there is therapy available for Guilliam-Barre Syndrome, and that's why it's very important to try and distinguish between these two causes.

QUESTION: And were you able to give some indication as to how sick they are? Can they move their arms, or is it just their legs that are affected? Are they able to breathe?

DR. SEJVAR: Essentially we've seen a very mixed bag. Usually again this is an asymmetric process, and by that I mean it affects one side of the body more than the other. Oftentimes it can affect only one arm or one leg. Several of the patients have indeed developed weakness of the muscles that help them breathe and have ended up on ventilatory support.

Again, I think it's a bit too early to tell about absolute prognosis, but it does seem that people who develop this weakness remain weak for quite some time.

CDC MODERATOR: Thank you. Next question, please.

AT&T OPERATOR: And that's from the line of Karen Mellon with Chicago Tribune. Please go ahead.

QUESTION: Yes. I have a question about the testing for West Nile virus in the blood and the treatments for that. Is there any cost estimate at this time for that?

DR. GOODMAN: No, there really isn't. This will depend in part on what technology is the best, whether it is an individual or pooled samples, and whether one of the existing tests can be readily adapted, and these are all things that reflect both laboratory studies and discussions that are in progress both within the government and within industry.

QUESTION: Another question if you don't mind. And it has to do with maybe putting this in perspective. There are obviously tests for HIV and other blood-borne disease to stop them from getting in the blood supply, but are there other viruses that we don't know about that may be transmitted through the blood already, or are you looking into more sophisticated testing for other diseases?

DR. GOODMAN: Well, you know, that's an excellent question. We do routinely consider, particularly with emerging diseases that can have serious outcomes in some patients like West Nile virus. We do attempt to anticipate problems and look for them, but as in infectious diseases in general and public health in general, it's not always possible to predict what the next problem will be or to potentially defend or study every single possible problem.

But I think that we are not--you know, there are a number of potential threats that we are addressing in various ways now. Examples include the theoretical risk that variant Creutzfeldt-Jakob disease, also called Mad Cow disease, could be spread in the blood. There have been no identified such cases, but FDA has taken some precautionary steps to reduce that risk.

So it think we do look at each of the known risks and try to put in place the appropriate actions or monitoring needed to protect against them.

Your question about unknown risk is a good one, and I think in the world of infectious diseases, there are always new diseases or old diseases which become manifest in new ways, and we need to keep looking out for them. One of the theoretically attractive ideas behind technologies that could inactivate potential pathogens in blood would be that if they are very robust and effective, they could offer the possibility to inactivate not only known pathogens, but unknown ones, so that's one of the potential advantages of that.

But there are, I should mention, other issues with those technologies, such as the fact that under--in the current, using the current measures of blood safety, the testing that is done, the careful evaluation of donors, et cetera, transmission of infectious diseases by blood has been extremely rare. If one then treats large numbers of units of blood to eliminate an infection from a rare unit, one has to be very sure that the effects of the treatment on those other units are not potentially harmful or don't potentially affect the quality of blood for the majority of patients that are receiving it.

And these are issues that the companies developing these techniques are very aware of, and the FDA is working very diligently to help them to evaluate those possibilities.

CDC MODERATOR: Thank you. We have time for one more question.

AT&T OPERATOR: And that will be from the line of Mark Kaufman, Washington Post. Please go ahead.

QUESTION: Yes, regarding the acute flaccid paralysis. There are 6 cases that you folks report here. Are there additional cases that are not being--you know, that are not reported in this particular file?

And similarly or--and related in a way, the--we've generally been told that the people who get quite sick from West Nile virus tend to be older or immune compromised in some way. It seems that most of these people are kind of middle-age and not necessarily sick. Is that something that is worrisome or noteworthy?

DR. SEJVAR: With respect to additional cases, indeed we suspect that more cases are occurring, and we are working on trying to identify additional cases.

With respect to sort of the age and health status of the people affected, it does seem that the--at least in the cases that we've identified, the age distribution tends to be sort of in the 40s to 50s, and that they--you know, are not severely ill to start off with. Obviously, I think we need to, you know, look at additional cases before drawing any sort of conclusion such as that.

CDC MODERATOR: Do you have a follow-up question?

QUESTION: In terms of the distribution of the cases, all of these are from Mississippi and Louisiana. Are there other cases from other parts of the country, or is that something you're aware of at this point?

DR. SEJVAR: That's something we're working to find out.

QUESTION: And also is there a predicted level of AFP from West Nile? You had said before that this was something that you were aware of as a possibility in the past, but is there a generally accepted level of AFP among West Nile people or people who have the disease?

DR. SEJVAR: Many people who develop West Nile virus do complain of weakness. In general, however, this is just kind of overall fatigue. What we're describing is actual weakness or paralysis of one or more limbs.

CDC MODERATOR: Okay. Thank you very much. And that concludes our telebriefing for today.

[End of telebriefing.]

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