CDC Telebriefing Transcript

West Nile Virus Update

September 12, 2002

CDC MODERATOR: Thank you, Brent.

And I'd like to take this opportunity to welcome all the reporters that have joined us on the call today. With us today from CDC is Dr. Lyle Petersen, the Deputy Director for Medical Science within CDC's Division of Vector-borne Infectious Diseases. Dr. Petersen will provide an opening comment. And also with us is Dr. Jesse Goodman, the Deputy Director for the Center for Biologics Evaluation and Research at the FDA, and Dr. Goodman is with us to participate in the Q&A.

So at this point I'd like to turn the call over to Dr. Petersen, who will provide an opening comment, and then we'll get to the Q&A. Thank you.

DR. PETERSEN: Thank you, Tom.

The Centers for Disease Control and Prevention continues to work with state and local health departments to help control West Nile virus. To date there have been a total of 1,201 human cases of West Nile virus infection reported to CDC from 30 states, the District of Columbia and New York City. There have been 46 fatalities reported.

CDC expects more cases of West Nile virus infection to be reported in the coming weeks as the transmission season peaks in different parts of the country. Exposure to West Nile virus through a mosquito bite is the principal means of acquiring infection.

CDC continues to urge people to take steps to protect themselves from being bitten by mosquitoes. These steps include eliminating standing water from around the home where mosquitoes are likely to breed, wearing long sleeves and pants and wearing insect repellents that contain DEET.

In addition, an investigation conducted by CDC, the Food and Drug Administration, the Health Resources and Services Administration, the American Red Cross and the Georgia and Florida Departments of Health, has confirmed transmission of West Nile virus from a single organ donor to four organ recipients. The source of the organ donor's infection remain unknown and the investigation remains in progress.

Subsequently, CDC has been informed of four other patients with West Nile virus infection diagnosed after receiving blood in the weeks before West Nile virus diagnosis. Investigations are ongoing and efforts are under way to contact donors of blood given to these patients, and other recipients of blood for these donors for follow up in West Nile virus testing.

In each instance precautionary measures have included a withdrawal of any remaining blood products obtained from the donors whose blood was given to these patients. Initial testing on some blood products from a few donors suggest that these donors might have had West Nile virus infection at the time of donation. These results are preliminary because all of the specimens available for testing in these investigations were initially processed for blood transfusion purposes which could affect test validity. Therefore, additional follow up testing and epidemiological investigation of these donors are necessary.

A large number of West Nile virus infections as a result of mosquito bite are occurring in the United States. By chance alone, some of these persons will have received blood transfusions. Recent receipt of a blood transfusion by a person with West Nile virus infection does not necessarily implicate the transfusion as the source of infection.

CDC and FDA are continuing to work in collaboration with blood collection agencies and state and local health departments to investigate whether West Nile virus can be transmitted by blood transfusion.

CDC MODERATOR: Okay. Brent, I think we're ready for questions, please.

AT&T OPERATOR: Very good. Thank you, sir.

And, ladies and gentlemen, as you just heard, at this point we'll enter into our Q&A session and we would ask that you would queue up for a question just by pressing the 1 on your phone keypad. Now, you will hear a tone indicating that you've been placed in queue. And just as a note, should your question or concern be addressed before you're called on, you may remove yourself from the queue by pressing the pound key.

And first we go to the line of Seth Borenstein (ph) with Knight-Ridder. Please go ahead.

QUESTION: Yes. Dr. Petersen, you talked about a few donors with testing of the blood products may have shown West Nile. "A few" is such an amorphous word. Can we get some specific numbers on how many--going to those four patients with West Nile virus diagnosed after receiving blood, how many blood donors are we talking about that these four received blood from? In other words, how many overall people do you need to test? And of those, how many--specifically, how many of them may have had West Nile virus in the blood from the tests that you've seen?

DR. PETERSEN: More details are provided in--in the MMWR, but I will recap the information. So far, including the blood transfusions that the organ donor received, plus these four other investigations, we're currently investigating appropriately 100 donors in total.

Investigations--of all of these investigations, we have tested available specimens from 2 of these--in two of these investigations. And one of--and both of--neither one of these investigations was the organ donor case, because there are many, many, many donors for that person, and that process is in progress.

For the two investigations that we have mostly completed, in one of them there were a total of 17 donors, of which we were able to obtain specimens at the time of donation from 15 of these. 3 of these 15 showed evidence of viral nucleic acid or the genetic material of the virus.

In another instance where there were 2 donors, neither one of these donors had evidence of viral nucleic acid or evidence of virus in those specimens.

QUESTION: Okay. Just to follow up then--and this might be more for Dr. Goodman--given what we know about the prevalence of West Nile and how--for every person who feels sick, there are probably 200 people who have it in their blood and just don't know it, have you figured out any--have you done any modeling or computer estimates to figure out in the blood supply what percentage might be--might have West Nile viral--you know, West Nile in it?

CDC MODERATOR: Dr. Goodman?

DR. GOODMAN: Well, actually, Dr. Petersen published the only study which has done this in a mathematically sophisticated way, and his study, which was published in the "Journal of Transfusion", I think last month--Lyle could amplify on it--used information from the intensity of the epidemic in 1999 in New York, and an assumption that--that the mean duration of the time that the virus was in the blood was about 6 days which was derived from all the available studies.

And they used mathematical modeling and estimated an incidence of somewhere in the realm of 1 to 2 people in 10,000 who might have viremia or virus in the blood, randomly at a time of donation.

Now, as Lyle and his colleagues said in that article, this is a model there's a lot of assumptions, on some of which would tend to make the incidency higher than it might be, and some of which could go the other way. But it was an attempt to get a feeling, and that in part, and our understanding that the virus can be in the blood for short times in asymptomatic people was what led FDA to issue an alert on August 17th about this possibility, and at least to have a high level of caution in endemic areas about the symptomatic people.

But in answer to your question, you know, the gene amplification result that Lyle mentioned in one of the donors--excuse me--in donors from one of these West Nile patients was fairly surprising, and, you know, based on at least CDC and other understanding of the dynamics of the epidemic and of the time that virus was in the blood were unexpected. And I think those are among the many reasons why there's an ongoing investigation using other testing methodologies in these cases, to try to get a fuller picture of this.

And just to reiterate what Lyle had said, in none of these cases at this time is it considered proven that transfusion transmitted the virus. But let me turn that around and say that, you know, at FDA, we are very concerned about this. So is CDC. We regard some of these findings as suspicious but in need of further study and confirmation. In general we're preparing as if this could turn out the be a real problem and hoping that it will not be, but we believe it's always better to be prepared in such a circumstance and to collect as much data as we can. And that's ongoing.

I don't know, Lyle, if you would like to add to that or give your perspective on possible risk?

DR. PETERSEN: As Dr. Goodman mentioned, that I had actually done the modeling, and the modeling that showed the potential risk would be about 2 per 10,000 donors. But this--again, this was modeling done under the conditions of the epicenter in Queens in New York in 1999, where there was a substantial West Nile virus outbreak.

We have no way to assess whether those numbers like on this modeling exercise produced a valid number or not. We think it probably is in the right ballpark. But places where there's less West Nile activity than an epicenter in Queens in New York in 1999 would be expected to have less of a risk.

And so I think the bottom line behind this is that there is a potential problem. We are investigating it. We are concerned about it. But for the average person, if they need a transfusion, the benefits of getting that transfusion are going to far outweigh--excuse me--far outweigh any risk of getting that transfusion, including the risk of getting West Nile virus.

CDC MODERATOR: Next question, please.

AT&T OPERATOR: Very good, sir. Thank you. And next the Fox News Channel's Steve Brown. Please go ahead.

QUESTION: Thank you very much. This question may be more epidemiologic than perhaps is necessary, but I have a question in regards to geography, where these cases are, the four investigations involving the suspected blood transfusion, and also the cases involving the organ donations. Could you give us an idea of geography that we're talking about? We're kind of concerned about this in the Upper Midwest because there seems to be a great, high concentration of cases here in the Illinois and Ohio areas. So we're trying to find out if these are also somehow perhaps related.

DR. PETERSEN: Right. The investigations right now involve a number of states. Among the states that we're most actively looking at and associated with these particular possible transfusion-related transmissions are North Dakota, Louisiana, Mississippi, and Georgia.

QUESTION: In regards to the organ donation cases, are those also mainly in the South?

DR. PETERSEN: That's the one that we're concerned with mainly in Georgia, although that donor had received products from--excuse me, that organ donor had received blood transfusions from donors from a whole number of states, and we're currently trying to track those back at this current time.

QUESTION: One follow-up, and again about geography. Is there a theory as to why it is so many of these cases are happening in Illinois? Currently, the State of Illinois reports 314 cases, and I believe it is 16 deaths--excuse me, 13 deaths currently. Is there a reason why so many of these cases seem to be centered in Illinois? That would make approximately a quarter of the cases or something approaching near a third of the deaths all happening in this state. Is there a theory as to why?

DR. PETERSEN: Well, I don't think we know the answer to that for sure. People have been trying to study these kinds of epidemics for years and have never come up with a very good explanation to my reckoning of why these epidemics occur in certain places in one year and other places in another year.

Now, if you look back at St. Louis encephalitis, which is a related virus to West Nile virus--and St. Louis encephalitis has been here in the U.S. for years. In 1975 there was a very large outbreak of St. Louis encephalitis virus that involved nearly 2,000 cases of encephalitis, and this was a multi-state outbreak that occurred throughout the entire Midwest. And states like Illinois and Ohio and states in the Upper Midwest were very heavily affected.

We kept this in mind very early on when we began to recognize that there was--there could potentially be a very large West Nile virus epidemic going on in the Midwest this year. And that is one of the reasons why we gave supplemental funding to Illinois and surrounding states very early on because we recognized that there was a pattern, a potential for a big outbreak in the Upper Midwest based on historical data from St. Louis encephalitis virus.

AT&T OPERATOR: Next question from Robert Bazell (ph) with NBC. Please go ahead.

QUESTION: Have you gone back and looked at all the other reported cases this year to see who else, if anyone else, if any of them had a transfusion?

DR. PETERSEN: No, we have not, and this is a discussion that we are currently undertaking right now. What we may consider doing is maybe looking in selected areas and doing a more systematic look. Right now what we have done--and as you can see from reading the MMWR, we are asking physicians who have potential cases to report them to local health authorities so they can get in touch with us and FDA so we can investigate these cases.

DR. GOODMAN: Lyle, Jesse here. Could I make one comment?

I think, again, we're taking these very seriously. We're very, very concerned. We are trying to take some actions to be prepared if this does turn out to be a significant public health issue in terms of transfusion transmission. But one thing that I think is important to keep in mind without trying to minimize the importance of these investigations is that, for instance, in these cases that have been reported to the CDC, again, at this time all of those individuals had known opportunity for exposure by a normal route.

Another point in terms of the kind of retrospective look at West Nile patients to see if they got a transfusion, some of the same characteristics that make people have West Nile disease and symptoms and much higher risk of that, such as age, possibly other medical illnesses, are also the same things that lead to a higher likelihood that somebody may have received transfusion.

So that doesn't rule any of this out at all, but it means that in evaluating reports and situations, we need to keep that in mind. That's really, you know, what we call looking at confounding possibilities when you do epidemiologic studies.

One other point that sort of stems from that is that in a way we're--there's certain kinds of information or case reports which, if they developed, would be much stronger evidence to support the idea that there could be a significant problem. And that could be, for instance, if a case developed in a recipient of a blood product who was in an area where there was no known natural transmission or if, as in the organ donor, cases developed in multiple co-recipients of blood materials from a single donor.

So part of the purpose of CDC ratcheting up the alert and wanting the public to be aware, you know, rather than panicking people or scaring them about a risk right now that we don't know very much about and where our knowledge is evolving, it's also to increase awareness so if there is a risk here we can identify it as soon as possible.

CDC MODERATOR: Next question, please.

AT&T OPERATOR: Certainly, sir, and thank you, Mr. Bazell.

Next we go to the Washington Post, David Brown, please go ahead.

QUESTION: Yes, Dr. Petersen, in your introductory remarks, you suggested that these--the findings of, you know, viral material might--you didn't really explain it in detail, but might be false positives, they may be an artifact of the preparation of the blood. Can you go into that, explain that a little bit more fully? And, presumably, that's the Mississippi case that Dr. Thompson talked about last week. And, also, if we can get a full identification of Dr. Goodman, including his first name, I got on a minute or two late and didn't catch that.

DR. PETERSEN: Why don't we start with the ID of Dr. Goodman, and then I'll go on to the other question.

CDC MODERATOR: It's Dr. Jesse Goodman, who is the Deputy Director for the Center for Biologics Evaluation and Research at the Food and Drug Administration.

Lyle?

DR. PETERSEN: Okay. Let me just say what this test is. It's a test called the polymerase chain reaction assay, and it's a particular--it's a quantitative test to look at the viral genetic material. The test is extremely specific for detecting West Nile virus.

What the test measures, as I said, was viral genetic material, so it does not measure whether there was live virus in a sample. It just says there's genetic material but we don't know whether the virus was alive or dead.

Now, this test, along--as with any laboratory test, there are a certain number of tests that are false positives or false negatives. We do not know what the sensitivity or specificity of these tests are in the types of samples that we are testing. These samples were collected under conditions suitable for blood banking; for example, anticoagulant was put in them. And we don't know what the effect of that anticoagulant is on these assays.

And so--and part of the problem is that there's very limited amounts of retained specimen that are left over in these specimens, so it's really impossible to do every single laboratory test that we would want to do to try and confirm the results in these particular specimens.

So I think what these results really do suggest is that there was viral genetic material there. We do not know whether the virus was alive or dead, and we also do not know if these are false positive tests.

QUESTION: Okay. Well, I understand that the operating characteristics of the test in this sort of material is not fully known. But I guess--is there any reason to believe that these are false positives? You know, does the anticoagulant frequently get contaminated with, you know, virus from--with genetic material from, you know, vector-borne viruses? I wouldn't think so.

DR. PETERSEN: It would be unlikely. I think our take on this is that these results are highly suggestive there was viral genetic material in these samples, though we cannot say with 100 percent certainty.

QUESTION: Okay. Are these--is this the Mississippi case, the 17--

DR. PETERSEN: Yes, it is.

QUESTION: Thank you.

CDC MODERATOR: And thank you, Mr. Brown.

Next in queue is Anita Manning with the USA Today. Please go ahead.

QUESTION: Hi. Thank you. Dr. Goodman, you have made reference a couple of times to the fact that FDA is preparing just in case it does turn out that the virus is in the blood supply. And I'm wondering if you could be specific about how you can prepare for that and what's going on.

And the other question that I have is for Dr. Petersen, and it's about the epidemiological curve of this epidemic. I mean, have we peaked? Do you know yet? Or is it still too soon to say? And I will put you back on mute. Thank you.

DR. GOODMAN: Well, thanks for the question. It's a very perceptive question because it is difficult at this point to define precisely what steps we might need to take, so I want to be very clear about that. That will depend on the information developed in these investigations.

In addition, to better understand that we are working closely with CDC and the blood community to rapidly implement some additional studies that might help us determine the frequency, if any, of viremia out there among blood donors and the then possibility and efficiency that that could transmit infection. Some of those studies may be able to be implemented and get some results in rather a short time frame. Others may be more sophisticated and get better information but take longer.

The one thing we are doing to get ready is working very hard to get whatever information we can from these cases of possible transmission and then looking a little more broadly to get an understanding of, if there is a problem, what the dimensions might be.

Now, what can we then do? Well, number one is we can--there are two kinds of interventions or possibly three that one could consider if a problem is demonstrated to be going on and there is a need for enhanced public health protection or safety measures for the blood supply. If that need developed, one would be if one could develop, could define--and this is where we would want to work closely with CDC and the state to see if this were even possible. But if one could define populations of donors that are specifically at the highest risk of potentially having been exposed to and have a short period of virus in the blood from West Nile, one could potentially exclude certain individuals for those time periods in those geographic areas from donating.

This is something that needs more discussion and modeling, whether that could be effective, and if so, how effective. But that is one kind of intervention that could be complicated--excuse me, contemplated were there a need to arise. Okay.

Another one which has been discussed much, both, you know, within the public health and blood system and with the media, is, again, were this to be a significant public health threat to the blood supply, one could consider specific testing of donor samples for presence of virus. This is done, as you're aware, routinely for several of the viruses that have been identified to be important transfusion-transmitted diseases like HIV and hepatitis C.

So in terms of that, that's not something that can happen overnight. CDC, several of the state labs, and others have developed tests to detect small amounts of West Nile virus in specimens and have used those primarily in clinical diagnosis and in public health laboratories. These are being used for specimens where there's a high likelihood of finding this because they're patients suspected of having disease.

But the basic technologies are similar to technologies that are now in place to detect very small amounts of HIV or hepatitis C in our blood supply, and if a need develops, we are hopeful and we would certainly do everything we can to assist in translation of technologies that are really used now in the research or public health setting to whatever the need might be more broadly.

Now, in terms of what we're doing along these lines, we are already making efforts to bring together folks who have these tests in various developmental stages with people who are experienced at implementation of blood screening, whether it's the medical diagnostics industry or the blood industry and community. So we--although the need to do this has not been identified yet, we are trying to jump-start that in the eventuality that it were needed.

Finally, one other comment about screening. Blood supply, similar to screening donors, is that it is possible that that could be targeted if there were a time or a place of need on, again, the donors perceived where there might be the most risk of West Nile infection, or if you could identify a kind of blood recipient who was at risk of getting disease, one could potentially, if capabilities were limited early on, at least screen materials intended for those uses. But we wouldn't want to do that unless we knew who was truly at risk.

So, again, to recap, a very evolving situation. We're not sure yet that there is a risk. It's biologically plausible. We're concerned about these reports, so we do want to prepare as if this is a problem and get the ball moving on all of these fronts while we're getting more knowledge and information. And that's the situation.

CDC MODERATOR: I think, Anita, the second part of your question was about the epidemic peaking in different areas. is that correct?

QUESTION: Yes, that's right. Thank you, Tom.

CDC MODERATOR: Lyle?

DR. PETERSEN: We have some--our data suggests that the epidemic has peaked in the Southern United States, although transmission is certainly still ongoing and people need to take precautions.

In the Northern United States, we do not have evidence yet that the epidemic has peaked.

We would expect, based on data from the 1975 St. Louis encephalitis outbreak, that the epidemic in the North-Central United States will peak sometime in the next week or two.

CDC MODERATOR: Next question, please.

AT&T OPERATOR: Certainly. Thank you, Ms. Manning.

Next we go to Paul Monese (ph) with WCBS-TV. Please go ahead.

QUESTION: Dr. Goodman, I know that there's been great concern about scaring people in terms of dissuading them from donating blood. How practical would it be to hold the blood out for a couple of weeks while it was being tested and then put it back into the supply chain?

DR. GOODMAN: Okay. Well, you know, two points here. One is you mentioned donating blood, and I think it's very important--and we have made these points before from both FDA and CDC and the Department of Health and Human Services--you know, that donating blood is a completely safe procedure. You don't--in this country with modern blood collection methods, you don't get a disease from donating blood. And so, to the extent--and right now, in fact, in this country blood supplies are low. The reserve margin is low, and when you consider some of the more major issues of our time--threat of terrorism, et cetera--plus the much more positive thing, how patients benefit from transfusions and transplants, you know, we really do want to encourage people to donate. That voluntary donation system is one of the things that keeps America's blood supply the safest in the world right now, and that's important to state.

In terms of your question of whether you could hold blood out and test it, right now the capabilities to test tens of thousands, hundreds of thousands, millions of units of blood are not there. If this is needed, the ideal approach would be to transfer some of these technologies now in use in small numbers of samples at diagnostic and public health labs into a situation where there is enough validation that these tests will perform properly, where they can be used more broadly. And in that case, as is done with HIV and hepatitis, there's not--they can be done very rapidly, and there's not a need for holding the blood out for long periods of time.

But, you know, as this situation evolves, if there were a much more significant problem, I think we would have to explore any and all options as to how to deal with it. I mean, clearly, we do want to keep blood extremely safe.

QUESTION: Is one option--am I still on the line?

DR. GOODMAN: Yes.

QUESTION: Is one option actually not accepting new blood for a period of time, perhaps until the first frost or something along those lines in areas where this is quite significant in terms of the infection level?

DR. GOODMAN: Well, I don't want to put anything off the table, but as I had said earlier, I think if the dimensions of this problem appear significant--and that's an if. There is an ongoing investigation here and, as stated, there are at this time no proven cases. But if that appeared--dimensions appeared serious and we could localize and locate at-risk donors within geographic areas, I think that would definitely be an option whether to exclude those donors for a time or if we were able to ramp it up to test in those kinds of areas. That's an absolutely credible point if there's a problem.

One thing that I'll just add on because I forgot to mention it before, but another technology that FDA has been working with industry to try to bring along is what is called pathogen inactivation where there are treatments that can be used on blood products to reduce or eliminate infectious agents such as a virus like this that might be there.

These are still in the research stage, but, again, some of them are very promising. And if this turned out to be a major problem with a major risk, one could explore a potential role for these in those areas. But these are not without issues because you do want to remember that for the overwhelming majority of people who get blood, you know--and here I mean, you know, the risk from the common infectious diseases, you know, can be as low for HIV and hepatitis as close to one in a million. For the overwhelming majority of people, even if West Nile is a problem, the blood that they get is extremely safe and offers no problem.

So if we are--if we do contemplate doing things which may through a treatment change the characteristics of that blood that's transfused, we want to be sure that not only have we eliminated risk for that rare patient who might get transmitted a virus like West Nile, but we haven't at the same time caused any risk for the overwhelming majority of people who do well with a blood transfusion now.

Those are the kind of complex risk/benefit assessments that FDA works with sponsors and manufacturers to make all the time. But I'm just bringing it up because, again, this is a dynamic situation, and whether it's perhaps well into the future, that's another exciting tool that's in the armamentarium, potentially at least.

QUESTION: Dr. Goodman, if I can ask one follow-up here and then I'll let someone else get on. I'm just wondering where does it stand right now in terms of the random blood sampling that you had mentioned, I believe it was last week. You were considering randomly testing blood around the country for the presence of virus.

DR. GOODMAN: We--CDC has the lead on that, and we're working with them and others to try to get that going in short order. So there was, for instance, a long phone call yesterday discussing the logistics of getting some of these studies up and running. The blood organizations have indicated a willingness to be very helpful on this. It may sound simple. It's not always the simplest thing in the world to do this. We want to be sure that if we do it, the data is usable and interpretable. But I think that the--you know, I'm hoping that those studies, at least some, can be initiated in a very short time frame. I'll let Lyle perhaps comment on that.

DR. PETERSEN: Yes, we would like to initiate these kinds of studies as soon as possible, and, in fact, discussions are going on as we speak about doing that with some of my other colleagues in the blood banking organizations.

CDC MODERATOR: Next question, please.

AT&T OPERATOR: Certainly. Let's go to the Atlanta Journal Constitution's Maryn McKenna. Please go ahead.

QUESTION: Hi. Thanks very much for doing this. I want to say at the start that I cannot mute the phone I'm on, so if the noise of my keyboard is a big problem, go ahead and mute me. But I do have a follow-up so please don't lose me.

First, Dr. Petersen, some clarifications. You have four transfusion recipients aside from the organ donor who appear to have some degree of West Nile virus that may be associated with the transfusions. One of them is the previously mentioned Mississippi case. Is the Georgia case one or the two organ recipients in Georgia, or is it someone totally separate from the organ donations? And could you discuss the condition of these four recipients and whether any of them had previous underlying health problems that would have made them more vulnerable?

DR. PETERSEN: The Georgia person is the investigation going on with the organ transplant donor. So the other four are in other areas. There are two in Mississippi, one in Louisiana, and one in North Dakota.

Now, as far as the health status of the recipients, let me just think about this for a second.

All three of these--or three out of the four had previous chronic diseases. One out of the four was a previously healthy person.

CDC MODERATOR: Ma'am, your follow-up?

QUESTION: I need to--am I back on the line?

AT&T OPERATOR: Yes, please, go ahead, ma'am.

QUESTION: Okay. Thank you. Sorry. You made the point that all these people live in areas where there is ongoing transmission of West Nile virus through the normal means of a mosquito bite. Can you explain how you'll be able to sort out in the lab whether the infections that have shown up in these transfusion recipients came from a transfusion or came from a mosquito bite before or after the transfusion, given that there's only one strain of virus circulating in the country?

DR. PETERSEN: That is an excellent question, and you have struck at the heart of the problem. There is no single laboratory test that's going to tell you whether the person got it from a mosquito bite or from a transfusion. So unless something highly unusual happens, like a transfusion recipient in an area where West Nile virus transmission is not occurring, let's say, Washington State or something, or some place, it's going to be very difficult to sort out natural mosquito infection from transfusion infection.

And so what's going to have to happen here is that we are going to have to do a number of investigations in a number of people to try and see if we can fit together some common epidemiological thread among all of these in order to make a case for West Nile virus transmission via blood transfusion or not. And so a number of investigations are going to have to be done.

It's sort of like in this case it's not going to be a black and white situation. It's going to be like a court of law where you have to get enough evidence that the preponderance of evidence suggests that this is occurring, and that's the process we're currently doing.

CDC MODERATOR: Next question, please.

AT&T OPERATOR: And thank you, Ms. McKenna.

We'll go to Diana Gonzalez with WTVJ. Please go ahead.

QUESTION: I actually have a follow-up to the question you just answered. For example, one of the cases of the four possibly transfusion-related cases is in North Dakota where there seems to be not that much viral activity, only four cases reported. Is that case of particular concern to you?

DR. PETERSEN: This is a person--first of all, there is West Nile virus transmission going on in North Dakota. There may be fewer cases in North Dakota simply because there's fewer people to get exposed. But we don't know that for sure.

But what we do know regarding this case is that we have ample evidence that there was West Nile virus transmission going on in the vicinity where this person lived. So it is highly likely that this person as exposed to mosquitoes that could have had West Nile virus infection.

QUESTION: Okay. I also have a question for Dr. Goodman, and that is that he keeps saying that they're taking preparations in case they figure out that it's a significant health threat. Can you give us a time frame as to when you will know whether this indeed is a significant health threat to the blood supply?

DR. GOODMAN: I would like to say we would like to know very soon, but due to a number of the complexities that you have heard about in terms of determining the cause of some of these infections, this may be, you know, more difficult than we think.

We're kind of on a little bit of a rollercoaster here, all of us who are involved in this. People are working very hard to obtain samples from these cases, to obtain additional data, to get other studies in gear. And it could be that we receive data within the next few days that tells us that some of these results to date are not likely to indicate in these cases transmission or are the opposite. And that could, you know, sort of change the universe and the feeling for us here about risk. But I think in fairness, it's not a situation that we control. We don't know enough about the biology and transmission of West Nile virus to reach--to reach a conclusion right now. This is evolving as we speak. We're all actively seeking out as much new information as possible. CDC is working to set up additional studies and to investigate these cases very hard. And what I'm really saying is that we want to be as positioned as possible to deal with any risk in the best way that we can, and I think that's a fair statement. We are not--you know, humans don't always control everything, and we're putting the best science and the best people, and working with some, you know, very helpful and cooperative folks in the states in the blood community to try to answer precisely the question you have as quickly as it can be answered.

CDC MODERATOR: Brent, how many more questions are in queue, please?

AT&T OPERATOR: At this point, sir, we have 3 participants that are all follow-up questions.

CDC MODERATOR: Okay. We'll take those 3 and then we'll stop. So next question, please.

AT&T OPERATOR: Very good, sir. Thank you.

And let's go to David Brown once again with the Washington Post. Please go ahead.

QUESTION: Dr. Petersen, could you just give the kind of basic, you know, facts that reporters always want? For instance, the case in which you looked at two samples, donor samples, and neither of them showed virus. Was that in Mississippi? Is it the recipient or the person that has West Nile virus possibly from a transfusion in Mississippi a man or a woman, you know, a little bit about the Dakota person, Louisiana person, you know, just the kind of basic stuff that we want.

DR. PETERSEN: Yes. I'm sorry. I think I'm going to frustrate you here because there are real issues of confidentiality and I do not want to go into the specifics of any one of these cases.

AT&T OPERATOR: And thank you, Mr. Brown.

Our next follow up comes from Maryn McKenna (ph), once again in Atlanta. Please go ahead.

QUESTION: Hi. Thanks for letting me follow up.

Dr. Petersen, I wanted to go back to something you said earlier, which was that the organ donor who had received a number of transfusions, turns out to have gotten blood from a number of states, and because of the complexity of that, you have sort of put that part of the investigation aside.

Following up on that, are you--is the CDC or is the FDA asking any questions about whether it's wise to keep moving donated blood across state lines in light of these investigations?

DR. PETERSEN: Yes. Thank you for asking this question. I think you're misinterpreting what I said. It's not that we've put the investigation aside. We're actively doing this investigation in conjunction with the Red Cross and state health departments. But what I am saying is because there are so many people involved, involving so many different states, that it's going to take a while to just track down that many donors and that many recipients of products made from those donors. It's mainly a logistical problem simply because this person got a tremendous number of transfusions.

QUESTION: Didn't mean to suggest that you weren't still investigating, just I thought you said--

DR. PETERSEN: No, no. We have gone back and we have been able to track down all of the donors, at least know who they were and also track down who are all the recipients of those donors. But what the complexity is, is actually going out there and finding all these people, and getting repeat blood tests on them and talking to them, getting questions about their health. That's mainly a logistical issue. And again, that's not necessarily related to where they came from, it's just the sheer number.

QUESTION: I appreciate the clarification. Sorry for misunderstanding. But I don't think that changes my question, which is that we had an organ donor here in Georgia who received blood apparently from a number of areas. So given that, does that cause you to think or the FDA to think at all about the movement of donated blood across state lines, given that the intensity of viral transmission may be different in some geographic areas than in others?

DR. PETERSEN: Yes. I would like to defer this question to Dr. Goodman.

QUESTION: Okay.

DR. GOODMAN: I think it's a good question, and it's connected to some of the kind of what-ifs that we discussed earlier. I think if--you know, just to recap, in that case in Georgia with the organ donor, we are concerned about the possibility that a transfusion may have been involved, but that's still under investigation. So we just need to be clear about that, and that was another individual with natural exposure.

But your question is a good one, and I think if there is a problem with transmission through the blood supply, and if we can identify areas that are at highest risk of having donors who might be infected without knowing it, even for a very short period of time, you know, one strategy could be to not--I wouldn't put it at not cross state lines, but, you know, consider whether those people for that period of time shouldn't be donors. So if they're a problem, that could be a strategy.

Now, in terms of implementing that strategy or the kind of strategy you're saying about importation of blood, there are a number of issues. One of them was raised by Dr. Petersen's initial update to you on epidemiology, that the disease, I think he said 41 states. et cetera, so the practicality of doing that in a simple way.

And then the other issue is that again if this is going on, there is a risk to people of potentially not being able to have blood, and depending on the risk and nature of this possible infection, I think it would be better if we could deal with it without creating a new risk that people don't have blood.

So I think that it has to be on the table as to whether if there are particularly high risk donors or areas, and transmission turns out to be a problem, such a measure should be considered, but it wouldn't be ideal for the reasons I'm saying. But if the risk is huge or turns out to be huge, I think we have to consider every measure we can then for intervention.

CDC MODERATOR: Brent, let's make this our last question, please.

AT&T OPERATOR: Indeed, sir, thank you.

And thank you, Ms. McKenna.

Our final question comes from Seth Borenstein once again with Knight-Ridder. Please go ahead.

QUESTION: Thanks so much, and it's a two-part question to finish it up. First--and both for Dr. Goodman. First, is there in your mind a threshold that in terms of the number of units that can be more conclusively tracked to blood transfusion, the number of infections? In other words, can you share with us what is sort of your threshold to make you kick in one of these three options you talked about earlier?

And then the other question I had is very early you mentioned that the gene amplification results from one of those blood transfusion cases as fairly surprising. Was that because of the number, the amount of West Nile virus, or what was fairly surprising about that?

DR. GOODMAN: Okay. Your first question was on threshold, and I think that given that we're dealing with evidence of varying degrees of strength and very complex clinical and public health situations, it wouldn't be very helpful or accurate for me to state a threshold. What I will say, you know, for instance there might be certain kinds of cases that only a couple could occur that would really raise concern. There might be others where the causation is not clear, where there were all these natural opportunities for infection, where the laboratory testing is unclear, that one might interpret differently.

So I think Lyle's analogy of putting together all the evidence like one might do in a trial, is not a bad one, and that we're going to weigh all the evidence from any sources, whether they're these case investigations which have a lot of difficulty in interpretation, or whether they're larger studies, or whether there are new things that come to light. We're going to weigh all that and try to do what's best to protect the health of the American people in real time.

What was the second question?

QUESTION: The second question was about--early on in response to my very first question, you talked about fairly surprising results from one of the blood transfusion recipients in the gene amplification. And I'm wondering was that in terms of the amount of virus--

DR. GOODMAN: No. Again, I would like to turn that over to Lyle, but, you know, I would say that based on the kind of intensity of transmission in areas, the very small percentage of people that after an epidemic seem to have acquired West Nile, studies that have been done looking for the nucleic acids in patients with active disease. All of those things would make you very surprised that in a small number of presumably randomly selected people, you would have that number of positives. They weren't of a level that was unexpected. I want to second that to my knowledge the tests were very carefully done.

But, you know, one of the reasons we're concerned about those results would be that, you know, they--there could be something different about those donors. It could be something that happened to those specimens that makes the results invalid. There are many alternative explanations, but we want to keep our minds also open to it could be that the disease transmission or whatever that is going on is different than what everybody thought, and that's one of the reasons for trying to, in the very near future, get more information outside of just these case studies where it's so difficult to always control the quality of the information.

I also want to just say that although we want to look at the whole picture of evidence, with blood we are pretty much on a precautionary model. If we have a high level of concern, there are situations where you may take certain steps without necessarily requiring proof like we would in a criminal court. So again, this is a moving target. We're looking at the evidence day to day.

We're having public discussions, including recently both CDC and FDA participated in presentations to both the Secretaries, Public Health Service, Advisory Committee on Blood Safety and Availability, and then today to FDA Blood Products Advisory Committee, and we're going to share information and seek input and try to make the best decisions in a difficult situation.

AT&T OPERATOR: And thank you, Mr. Borenstein.

With that, doctors, and Mr. Skinner, I'll turn the call back to you.

CDC MODERATOR: I just would like to remind everybody, probably if they received a notice about the media briefing, they've also received the MMWR, but all of the case counts, as well as a description of the investigation of blood transfusion recipients with West Nile virus infections is chronicled in the MMWR which is available to everybody, CDC's Morbidity and Mortality Weekly Report. And if you have not received a copy of that, you can call 404-639-3286 to receive that. [Report can be found at http://www.cdc.gov/mmwr/mmwr_wk.html].

Thank you every for joining us.

[End of telebriefing.]

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