CDC Telebriefing Transcript

West Nile Virus Update

September 5, 2002

MS. SWENARSKI: Thank you very much for all of your patience and for joining us this late in the day. We rescheduled for 6 o'clock because we really wanted to give you all the information we had, and we thought new information was coming in today and wanted you to have that.

Today our speaker is Dr. Lyle Petersen, West Nile virus expert here at CDC; and then also on the line we have people available for questions: Dr. Ed Thompson, the state health officer from Mississippi; and Dr. Steven Wiersma, from the Florida Health Department.

Dr. Petersen?

DR. PETERSEN: Good afternoon.

The Centers for Disease Control and Prevention continues to work with state and local health departments to control West Nile virus. To date, there have been a total of 854 human cases of West Nile virus infection reported to CDC from 28 states, the District of Columbia, and New York City. There have been 43* [*CORRECTION] fatalities reported.

CDC expects many more cases of West Nile virus 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 mosquitos. 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, the agency continues to work with the Food and Drug Administration, Health Resources and Services Administration, and the Georgia and Florida departments of health to investigate a cluster of cases of West Nile virus through transplantation of organs from one donor.

So far, three people who received organs from a single donor have been diagnosed with encephalitis due to West Nile virus. One has died, and the other two are recovering in the hospital. Also, today, a fourth organ recipient has tested positive by the Florida Department of Health Bureau of Laboratories and has been diagnosed with West Nile fever, a milder form of the infection.

CDC is also investigation the case of West Nile virus infection in a Mississippi resident diagnosed nearly four weeks after receipt of multiple units of blood associated with a surgical procedure. The patient reported having been bitten by mosquitoes on numerous occasions prior to hospitalization. However, as a precaution, remaining blood products from donors of blood to the patient have been voluntarily withdrawn from use. Preparations are under way to contact donors of blood given to the patient so testing for West Nile virus can be done. Similarly, recipients of blood components from these donors will also be contacted and tested for West Nile virus.

A large number of West Nile virus infections as a result of a 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 will be working with states reporting cases similar to the one in Mississippi to learn more about the likelihood of West Nile virus transmission through blood.

We're ready to take questions.

MS. SWENARSKI: Okay, first question, please.

AT&T FACILITATOR: Our first question is from the line of Marin McKenna from the Atlanta Journal-Constitution.

QUESTION: Hi. Thanks for doing this. Dr. Petersen, could you be a bit more specific about the circumstances around the woman in Mississippi? How was it that her infection was recognized? She supposedly received--this is an obstetrical procedure, she received numerous units of blood. Do you know how many donors and what the status is of tracking down those blood products on the donors? And then I have a follow-up.

DR. PETERSEN: Maybe I might refer this do Dr. Thompson.

DR. THOMPSON: Sure. I'll tell you what we're prepared to confirm at this point. We do have a patient who was diagnosed based on investigation of symptoms consistent with West Nile disease as having West Nile disease. The patient does meet the criteria under the surveillance case definition for West Nile disease, for a confirmed case of West Nile disease.

In the course of investigating that patient, it was then learned that the individual had received multiple units of blood and blood products in connection with the previous medical procedure. So the case was identified because the individual presented with signs and symptoms consistent with West Nile disease.

QUESTION: Dr. Thompson, do you have any sense yet--I understand that it's being said that this person also had had mosquito bites, but on the assumption that transfusions might be implicated, do you have any sense yet of how many units, how many donors? Do you have a handle on where other units from those donors are and whether there are any other recipients of units from those donors?

DR. THOMPSON: We are in the process, working with the FDA, with CDC, and with the blood bank involved, in the process of notifying all of the donors and also notifying any recipients of products from any of those donors. And I think it was pointed out by Dr. Petersen, as a precaution any remaining products that came from any of the donors connected with this case were recalled and will not be used.

Understand, we have no data connecting this individual with an infected donor. We are simply investigating that possibility because of the temporal relationship of the receipt of the blood products with the onset of West Nile disease. The individual does reside in the area of the state in which multiple human cases of West Nile virus have been identified, there's extensive mosquito activity, and there is a history of mosquito exposure. So it is not by any means a foregone conclusion that this is a transfusion-related case. We simply do not know whether it was or was not at this time. The investigation is ongoing.

AT&T FACILITATOR: The next question is from the line of Anita Manning with USA Today.

QUESTION: Thanks very much. My question, though, is with these new developments, does this not sort of underscore the likelihood or the prob--however you want to say it, that mosquitoes are not the only source of transmission and that what was once theoretical has now inched a little more toward reality in terms of other modes of transmission of this virus? And then I also have a follow-up question.

DR. PETERSEN: Okay. The one point I would like to emphasize is that mosquitoes, by far, are the mode of transmission of West Nile virus. There is absolutely no proof at this point that West Nile virus transmission by blood donation has occurred in the United States or else. This still remains a theoretical possibility. Because it is a theoretical possibility, we are investigating these cases to see if West Nile virus transmission in blood transfusion has occurred and the degree that it might be occurring. But we still think this will be a very rare event to occur.

What we have concluded, or come to a strong--I think a good conclusion here, the fact that we have four organ recipients who have West Nile virus from a single donor would implicate the fact that organ donation, or receipt of organs could potentially be a mode of acquisition of West Nile virus. However, as I emphasized, we still do not know about blood transfusion. It still remains a theoretical possibility at this point in time.

MS. SWENARSKI: Do you have a follow-up, Anita.

QUESTION: Yes, and actually it's a different sort of question. Can you tell me--you mentioned at the beginning the number of cases and the number of states. Can you tell me, have new states reported today? Has West Nile virus moved into any new states?

DR. PETERSEN: There are no new states that are reporting West Nile virus that I know of today. There are--I do not have my list from yesterday, but I'm not aware of new states.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: Is from Diedtra Henderson from the Denver Post.

QUESTION: Could you please, if you're able, tell me a little bit more about the timing of the Mississippi resident's--the exact sequence, when the surgical procedure happened, when the symptoms--you know, attach a date to what you know so far, please?

MS. SWENARSKI: Dr. Thompson?

DR. THOMPSON: The information that we have is that the identification of West Nile virus in the laboratory occurred approximately four weeks after the receipt of the blood products. However, the onset of symptoms was somewhat earlier than that, and the onset of symptoms was within the time frame that encompasses the incubation period for West Nile virus. So it is possible, based on those temporal relationships, that a transfusion might have been the source. This has, however, not been established and we only know that it is temporally consistent. But we have as strong evidence--as for anything else--that it is mosquito-borne as we do for transfusion association at this point in time.

QUESTION: May I ask a follow-up please? Are there any other risk factors for this particular person in Mississippi, any compromised immune system or age?

DR. THOMPSON: We're aware of no unusual risk factors in this circumstance.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: And we move on to Paul Moniz [?] with CBS-TV.

QUESTION: I'm wondering again regarding the Mississippi woman if you can give us more specific--I understand confidentiality is an issue here, but her age and the type of obstetric procedure that she was undergoing?

DR. THOMPSON: You understand correctly. Medical confidentiality is an issue. That's all the information I can give you specifically about the individual.

QUESTION: Follow-up question, if I may. Regarding the organ recipient, or I should say the organ donor in Georgia. It was talked about last time that the woman, the accident victim may have received as many as--multiple units of blood from 60 or more people and that 12 other people may have actually received that blood, too. Are those numbers still consistent, or have there been increases?

DR. PETERSEN: These are the numbers. These numbers are still consistent.

MS. SWENARSKI: Thank you. And if I could just tell the operator, we are expecting Dr. Jesse Goodman from the FDA to call in as well on the host line. Next question, please.

AT&T FACILITATOR: Is from Laurie Garrett from Newsday News.

QUESTION: Yes, I'm wondering if you folks go along with the calculus that was derived by New York City Health Department based on their study of the 1999 outbreak here, estimating a ratio of asymptomatic viremic cases to diagnosed to be roughly in the neighborhood of, what was it, 140:1. Whatever it was--pulling it up right now. But anyway, based on my calculation of it, that would mean more than 100,000 Americans have become infected with West Nile virus this summer. Do you think that algorithm makes sense? Would you think 100,000 sounds a reasonable guesstimate?

DR. PETERSEN: It is true that there's been several studies that have all been very consistent that have shown that for every 150 West Nile virus infections, approximately 1 results on a severe case of West Nile virus infection, meaning meningitis or encephalitis. So you are correct about this 150:1 ratio.

Now, as I mentioned earlier, there have 854 cases with West Nile virus infection reported to the CDC this year. Most of those do have encephalitis or meningitis, but some do not. And we're in the process of working with state health departments to determine the exact clinical characteristics of these 854 people. But from what we know, approximately 80 percent or so do have--of these cases reported to us, do have encephalitis and meningitis. And that is because we're specifically doing surveillance, looking for more severe disease.

Given the 854 people, and let's say that 80 percent of them have West Nile virus, encephalitis, or meningitis, and each one of these could represent 150 or more cases of West Nile virus infection, this would imply that tens of thousands of people have actually been infected with the virus this year.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: And it is from Ann Carrns, from The Wall Street Journal.

QUESTION: Hi, thanks very much. Can you comment--now we've got all four recipients from the single organ donor testing positive for West Nile. So can you say at this point that--have you effectively ruled out the mosquito bite option here? What are the odds that all four of them could have gotten it from a mosquito bite?

DR. PETERSEN: I would say at this point in time the evidence very strongly suggests that these transmissions occurred via organ transplantation. I do think that mosquito bite for these four persons is very likely at this point in time.

QUESTION: Okay. And can I just ask a housekeeping question here? The recipient who died, who tested positive for West Nile, is it correct to say the cause of death was West Nile encephalitis, or did he die from some other cause and happened to be infected with West Nile?

DR. PETERSEN: That is a determination by the patient's physician. What I can tell you is, is that on autopsy of this patient there was large amounts of West Nile virus seen in this person's brain.

AT&T FACILITATOR: The next question is from David Brown, from the Washington Post.

QUESTION: Yes, hi. I'm going to try this again with Dr. Thompson, and then I have also a question for Dr. Petersen.

Can you give us--I think it's unlikely we're going to be able to identify this person if you say that she's in her 20s, she got three units of blood, and she lives in the Delta or the coast or--you know. So can you just give us a little bit more sense of the details of this case?

DR. THOMPSON: I took my Hippocratic oath very seriously. Medical confidentiality precludes us releasing that degree of detail about the individual. I'm sorry, but I can't tell you more.

QUESTION: Won't it appear in MMWR in a couple of weeks in even more detail?

DR. THOMPSON: I don't know. Not from us.

QUESTION: Well, okay.

MS. SWENARSKI: And you had a question for Dr. Petersen?

QUESTION: Yeah, my other question for Dr. Petersen is, is it known whether after infection you have lifetime immunity or long-term immunity from reinfection?

DR. PETERSEN: The available evidence to date suggests that once somebody is infected, they will have long-term immunity. Whether they have lifetime immunity or not, nobody knows. But epidemiological studies done in endemic areas in the Old World do suggest that immunity is long-term. Related viruses, such as Japanese encephalitis virus and yellow fever virus, once persons get infected with those viruses, they do have lifelong immunity, so it's a pretty good suggestion that that would be the case here as well.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: Next we have Alysia Lane, with NBC-6 Miami.

QUESTION: Yes, based on the fact that we're here in Miami, that 71-year-old patient, can we confirm which hospital the transplant was done in and if it was the same as the other Miami-Dade resident?

MS. SWENARSKI: Dr. Wiersma?

DR. WIERSMA: All we're able to say at this time is that this transplant was done in a Jacksonville hospital. We're not specifying which hospital. But the patient was a resident of--is a resident of Miami-Dade County.

QUESTION: Okay. And my second question is with regard to testing and, obviously, trying to prevent this and the spread of it through other means such as blood donations or, you know, or any kind of transplants, what kind of testing--can you talk to us a little bit about the testing procedures and if they're going to be changing as a result of what's going on?

DR. WIERSMA: You're talking about the broader issues, and CDC will address those.

DR. PETERSEN: Yeah, about the testing procedures for transplant with respect to what, West Nile virus specifically?

QUESTION: Yes, because now we're discussing it being spread through other means possibly, aside from mosquitoes. So now what happens--I mean, are people that are taking blood transfusions or getting transplants, is there a cause for concern for those people, or is any new testing procedure going to go on now because of this?

DR. PETERSEN: I would like to emphasize that we do not know how the organ donor got West Nile virus infection. We do not know if that donor got it via mosquito bite or via transfusion. And this is why we're doing this investigation. So I think it's a bit too early to speculate on what kind of testing would be necessary in the future.

AT&T FACILITATOR: Next we have Colin Grey [?], with WIOD Miami.

QUESTION: For Dr. Petersen, the question is can you give us a prognosis for the 71-year-old patient who has just been diagnose with West Nile, the transplant patient?

DR. PETERSEN: This is the Florida patient?

QUESTION: Yes, mm-hm.

DR. PETERSEN: Dr. Wiersma?

DR. WIERSMA: What we can say is that the patient is recuperating with family, because she's out of hospital. We can't say any more than that.

AT&T FACILITATOR: [inaudible]. Please go ahead.

QUESTION: Thank you very much for taking my question. What I'm wondering is--and maybe this is a question for FDA, but would it be possible to do random samples to find out how widespread the virus is within the blood supply, if indeed it is widespread throughout the blood supply.

DR. PETERSEN: Is Dr. Goodman on the line at all?

DR. GOODMAN: Yeah, I'm on now. Yeah, that's a very good question, and we are discussing with CDC ways to try to accrue additional information as to if--whether West Nile virus is present in asymptomatic blood donors, and if so, what the frequency of that would be. The CDC modeling suggests it would be at an extremely low frequency because of the very short period during which individuals appear to have virus in their blood. But nonetheless, we believe that these recent concerns that have been raised certainly mean that we want to rapidly implement some clinical research in an effort to help define the problem better. So that's one approach to doing that, and we'll work with CDC to try to move those kinds of studies forward. And also, incidentally, the blood industry has indicated a willingness to participate in any needed studies.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: Next we have Dr. Sean Kenniff with WFOR CBS-Miami. [No response]

We'll move on to the next question, Bill Scanlon, with Rocky Mountain News.

QUESTION: Yes. If a person gets a mosquito bite, doesn't have any symptoms, donates blood, is the fact that he has no symptoms and has presumably suppressed that West Nile virus, is that good news to the recipient? Is it possible that that successful suppression will transfer to the person receiving blood, or is the person receiving blood, you know, for one reason or another just likely to receive--to get symptoms of West Nile?

DR. PETERSEN: You know, let me rephrase this a little bit. After infection with the virus, certain people will develop symptoms. Probably everybody will develop some kind of viremia, although we don't know that for sure. That means they may develop some virus that's present in their blood. Presumably people who are asymptomatic, who have not developed symptoms after West Nile virus, would have lower levels of virus in their blood for a shorter duration, or may not develop virus in their blood at all. But we don't have any good data to show that.

People who may be more likely to develop symptoms may be more likely to have virus in their blood, and possibly for longer duration, although there's obviously no really good data on this since nobody's going to do an experiment infecting humans with West Nile virus on purpose to measure this.

So what actually happens in humans is unclear with relationship to their symptoms. The one thing I would like to emphasize, though, is blood centers screen people for the presence of virus--I mean, for the presence of fever and any kind of illness, and exclude them from donating. So that would tend to eliminate people that may potentially have been exposed to the virus and may have the virus in their blood. It will reduce some of them, anyway.

QUESTION: Just to follow up, anything new from the Fort Collins lab on these tests of the people down in Georgia and Florida?

DR. PETERSEN: No new news yet.

AT&T FACILITATOR: Next is Miriam Falco with CNN.

QUESTION: Hi. Thank you for doing this again. I've got two questions. Number one, it's quite a jump from the almost-700 number to 854 human cases. Are there any places you would characterize as hotspots outside of Louisiana? And also, you mentioned the mosquito bite that the Mississippi patient had which could be the source, or the blood could be the source. Do you know if the mosquito bites were before or after, and how would you even be able to determine what the possible source of the West Nile infection is?

DR. PETERSEN: Well, it's impossible to know when the patient became exposed to mosquito bites. I mean, she--or potentially exposed to a infected mosquito. She lives in an area where there are many mosquitoes, and she reports having been bitten mosquitoes multiple times. She was unclear about the timing of any potential exposure to the virus, although we would say--probably would say that she was potentially exposed to the virus anytime while she was at home.

The only possible way to prove whether transfusion-related transmission did occur would be to find virus in leftover blood from those donations, or to show that a co-recipient of one of the products, from the same donor, had been also infected. Lesser evidence would be to show that one of the blood donors has West Nile virus antibody and thus could have potentially been infected at the time of donation.

Now, if all of the donors were negative for West Nile virus antibody at this point in time would suggest that the infection was acquired by a mosquito bite.

MS. SWENARSKI: Next question, please?

QUESTION: Wait a second, what about my first question?

MS. SWENARSKI: Can you repeat?

QUESTION: The other areas with--hotspots with a high incidence.

DR. PETERSEN: Right now, there--a large number of cases have been reported from Illinois--211 cases as of today. And that probably, next to Louisiana, that is the state with the largest number of cases. And we know that their case counts have been increasing in recent days.

MS. SWENARSKI: Thank you. Next question, please.

AT&T FACILITATOR: Tina Hessman, with St. Louis Post-Dispatch.

QUESTION: Hi. I was actually wondering about the way that you are reporting the number of cases. Yesterday you only counted 122 of Illinois' now-217 cases. Has there been a move to include preliminary cases, or are those all confirmed cases by CDC?

DR. PETERSEN: These have all been confirmed by the state health department and reported to CDC.

Just a bit of a correction--there were 211 cases reported to CDC from Illinois as of today. And I do not have the number from yesterday, but I believe it is around 150 or 160.

Now, the one thing regarding these large numbers of cases that may be coming in on a single day from a state, that is due to the fact that the states often do their testing on certain days, so a large number of results will come back on a certain day.

QUESTION: Then I have a follow-up. This is a completely different topic. I was wondering if we've found evidence of West Nile virus in mosquito species other than the Culex mosquitoes, and if those other mosquitoes are potential sources of transmission of the virus.

DR. PETERSEN: There are a large number of mosquito species that have been shown to be infected with the West Nile virus. In fact, there's been over 30 mosquito species to date. Some of those have been shown in the laboratory to be competent vectors for mosquito virus transmission--for West Nile virus transmission. But what is done in the laboratory doesn't necessarily mean what's important out in nature. So we still don't know exactly which mosquitoes in any given area are most important for transmitting the infection.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: Susan Lewis [sp], with Bottom Line Personnel.

QUESTION: Yes, I'm trying to get a handle on an apples-to-apples comparison of this year to last year. I had written that there were 66 cases last year, but I sense that some of it is reporting issues. Can you give me a sense of just what's going on?

DR. PETERSEN: In what sense?

QUESTION: In terms of the infections. Is it that last year the reporting was different, or is it actually a tenfold increase so far in the number of cases?

DR. PETERSEN: There is a massive increase in West Nile virus activity this year compared to previous years, over a wider geographic area. We've seen this, and it's not simply due to reporting artifact. Reporting in the U.S. has been excellent since the virus was first identified in the U.S. And this represents a true increase in human cases. The human data are corroborated by other data as well, such as dead bird reports and high proportions of mosquitoes in a number of cities having West Nile virus infection.

So we know that there's a lot of West Nile virus being circulated in nature and a concomitant increase in human cases.

QUESTION: So you would expect that it would go up next year, too, depending on weather, perhaps?

DR. PETERSEN: I cannot predict the future, but the one thing I would like to emphasize is, is that West Nile virus is an epidemic disease. So we would expect a pattern to occur like St. Louis encephalitis, which is a related virus that's present--has been present in the United States for years. And with St. Louis encephalitis, sporadic cases occur here and there every year, sometimes that are small outbreaks and occasionally there are very large ones.

For example, in 1975 there was a St. Louis epidemic in the Midwest that involved nearly 2,000 cases of encephalitis. We would expect over time that West Nile virus would behave in the same way, where you find a few cases one year, small outbreaks another year, and an occasional large epidemic, such as what's occurring this year. This has been the pattern that the West Nile virus has had in the Old World, where it has been endemic for many years.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: Laura Meckler, with Associated Press.

QUESTION: Thank you. Based on the patterns that you've seen in previous years or with similar diseases, how many total cases do you expect still this year? And do you expect that they're going to continue to show up even after the summer ends and possibly into the winter? And I have a follow-up.

DR. PETERSEN: I cannot predict how many West Nile virus cases will occur for the rest of the year. What I will say is, is that, historically, around the last week of August and the first week of September has been the peak of the epidemic. So we would expect in the upcoming weeks a lot more cases to occur, but this number begin to wane as September ends and October begins and the cooler weather comes.

It's hard to predict when transmission will stop. For example, last year we were surprised that we had West Nile virus cases occurring in New England in December. And that was because there was an exceptionally warm fall last year. Historically, mosquito-borne diseases can occur all year round in the Southern United States--Florida and Louisiana, for example. Although the number of cases that occur in the winter is obviously smaller, but they can occur all year round in those states. We would expect West Nile virus to be no different from, let's say, St. Louis encephalitis virus.

QUESTION: The other question is just a clarification on the organ donor who provided the--who you're investigating now. Were there two blood tests taken, or do you have two different samples of blood from that woman's stay in the hospital; and is there a difference in its West Nile? In other words, do you have a sample from early in her stay that does not show West Nile, that would suggest she got it while she was in the hospital? I heard something along these lines.

And also, Dr. Petersen, could you spell your name and give us your title?

DR. PETERSEN: It's Lyle, L-y-l-e, Petersen, P-e-t-e-r-s-e-n, and I'm the deputy director for the Division of Vector-Borne Infectious Diseases.

Could you repeat the question again, please?

MS. SWENARSKI: Operator, we didn't answer the previous question. We need to go back to the last caller.

QUESTION: Hello?

MS. SWENARSKI: Is that Laura? Can you repeat your question?

QUESTION: Yes. Do you have two samples of blood from the organ donor that would suggest she might have acquired the infection during her hospital stay?

DR. PETERSEN: Yes, we do. We have a sample of blood before any transfusions were given, and we have a sample of blood at the time the organ harvesting took place. The sample of blood that was taken before the transfusion did not have evidence of West Nile virus.

Now, I'd like to emphasize that that does not rule out the fact that she could have had a mosquito-borne virus--I mean, mosquito-borne infection, excuse--because she could have been infected with the virus by a mosquito before hospitalization and it just happened to be that she developed virus in her blood during her hospitalization.

Now, the only thing finding--if a positive sample was found before the transfusions, that would indicate that it was a mosquito-borne infection. But the fact that a positive sample before the transfusions was not found and the sample was in fact negative does not rule out a mosquito-borne infection. Is that clear?

MS. SWENARSKI: Is that clear, Laura? Okay, let's go on to the next question.

AT&T FACILITATOR: Next we have Mr. Nick Delasio [sp] with Associate Press.

QUESTION: Yes, Dr. Petersen, I'm just wondering about the geographic distribution, specifically--presuming the mosquitoes are the prime vector, any idea why there are so many cases here in Illinois? I mean, this is not a state that's really had that much in the past. I can think of 19th century examples, and as far as I recall, yellow fever never moved up past the southern bit of the state, whereas we're getting an awful lot of cases right here in the Chicago area.

DR. PETERSEN: Right. Mosquito-borne diseases are traditionally more common in the Southeastern United States, largely because of the climate and habitat there. However, mosquito-borne disease such as West Nile virus have occurred throughout the Midwest. And if you look back at the 1975 St. Louis encephalitis outbreak, which encompassed pretty much the entire Midwestern part of the United States, there were plenty of cases in Illinois at that time.

MS. SWENARSKI: Next question, please.

AT&T FACILITATOR: Next we have Marin McKenna, with Atlanta Journal.

QUESTION: Hi, thanks for the chance to come back with a second question. Dr. Petersen, or Dr. Thompson, I wanted to see if we could get a better sense of where the numbers are with regard to the part of the investigation that deals with the blood donors. In the Georgia and Florida cases, how far have you gotten on tests of recalled blood? Have you reached any of the other recipients of the blood? And in the Mississippi case, I don't think I heard a firm number, or even a rough number, of units of blood or donors. Could you be more specific about where you are in that investigation?

DR. THOMPSON: This is Ed Thompson. We have been able to identify 18 units of blood or blood products, in the instance of Mississippi, that could potentially have been a source of infection.

AT&T FACILITATOR: Next question, Andrew Kolpin [sp], ABC News Radio.

QUESTION: Thanks for taking the question. And just a brief one, since most of the others have been answered. In a non-medical sense, very generic, tomorrow a lot of people are going to be reading this and hearing this, saying, well, they don't know whether the blood is tainted or not. What kind of assurance can you give, or more importantly, what would you say to people who are now expecting to receive blood in areas where there is West Nile virus, to alleviate their fears, if in fact you can?

DR. PETERSEN: I can make a very strong statement, and that is, is that the person has a medical need for blood transfusion or a donated organ, they need that blood and they need that organ. And West Nile virus is--it's going to be proven, I think, that transmission via this route is very rare and probably not very common. So the medical need of getting blood, or the medical benefit of getting blood or organs far outweighs any potential risk of getting West Nile virus transmission from blood or organs.

MS. SWENARSKI: Is there a follow-up?

QUESTION: That'll do it. I appreciate it.

MS. SWENARSKI: Next is Michael Hibblen with CBS News.

QUESTION: Hi. To a degree this has already been answered, but can you give any more specifics on the gentleman here in South Florida who's become the latest to test positive after getting the organ transplant?

DR. WIERSMA: This is a 71-year-old female, actually had surgery in the Jacksonville area and, it's already been stated, is recovering there out of hospital. The patient does call Miami-Dade County home, but is currently in the Jacksonville area. That's all we can release.

AT&T FACILITATOR: Next we have Steve Mitchell, with UPI.

QUESTION: Hi. My question is for the FDA and the CDC officials. When this disease first hit here in '99, was the possibility of looking into whether it could be transmitted through organ donations or organ transplantation or in the blood, was that ever considered?

DR. PETERSEN: Dr. Goodman?

DR. GOODMAN: Well, there'd been, certainly, discussions of the fact that this and, you know, other commonly occurring virus infections can be transmitted by blood. I think that the feeling about this one was that the history in other countries and as the disease occurred here, you know, was of no such transmissions being known. And then the issue, and this is relevant to the last gentleman's question, too, that it appears that if the virus is present in the blood, it's for a very short period of time, that this made this an extremely low risk. And this also was particularly true at a time when the disease was, you know, far less common and just emerging in this country. And I think the increased emergence of the disease, the increased incidence of the disease, the increased spread of the disease, you know, turned our attention to being alert to this possibility again.

And, you know, I think in terms of the question--so I hope that's helpful. It has been something that has been discussed. There's been a couple of surveys, you know, looking at normal populations and the percentage of people who have antibodies indicating recent infection in past years, and these have shown very, very small numbers, so nothing to suggest that infection was commonly going on among healthy individuals in the past.

And I was just going to say, the comment about tainted blood. Obviously, we take any threat to blood safety extremely seriously, and that's being done in this case. And that's why these intensive investigations are going on. But again, the point that to all our knowledge, the presence of virus in the blood of patients is only for a short time means it's not like there are people, large populations running around with West Nile virus constantly circulating in their blood. It's very unlike the situation with HIV or hepatitis C, where patients tend to have infections for months to years to lifelong. And I think in terms of people understanding a little more about this risk, that's very important.

QUESTION: Could I ask a follow-up question? The FDA said that current procedures in place appear to inactivate viruses similar to West Nile. Has there been any research in light of recent incidences to look at whether it specifically inactivates West Nile virus?

DR. GOODMAN: The issue is, just to clarify for others, the issue of inactivation pertains to not the kind of blood that is generally transfused to, let's say, trauma patients, but more to what are called plasma derivatives, the kind of clotting factors of other substances given to people with special needs, you know, which are manufactured in plasma. And in fact, very closely related viruses are used in validating the efficiency of plasma inactivation of viruses. And the initial review of this information by FDA experts, you know, suggests that there is no reason to expect--well, let's put it this way, suggests that all the currently used processes should inactivate Flavy viruses, viruses in this same family. However, as a result of the concern, we're going to continue to look at that information very carefully in determining if there is a necessity to look at this with that specific virus.

I would point out that actually viruses of this class have been used to show inactivation for hepatitis C, which is very closely related, because there is no way to grow and work easily with hepatitis C in the laboratory, and that these viruses are sort of used as a surrogate to determine whether hepatitis C would be inactivated. And in fact, to our knowledge, these inactivation procedures are very effective for hepatitis C itself and have prevented any transmission of that virus.

MS. SWENARSKI: And we have time for one more question this evening.

AT&T FACILITATOR: It comes from Lee Hopper, with Houston Chronicle.

QUESTION: Hi, thank you. This is a question for Dr. Petersen. Can you discuss any assistance the CDC is giving to Mexico in terms of preparing doctors for West Nile virus and the potential impact the virus could have there, where living conditions might leave people more exposed to night-time mosquitoes?

DR. PETERSEN: Right. We're doing several things right now. One thing we're doing is we are funding studies to look to see whether the virus is down in Mexico and circulating in Mexico at this time. The other thing is, is that we have conducted laboratory training courses for people throughout the Americas to help get the diagnostics for West Nile virus up and running many countries throughout the Caribbean and South America. Because we fully expect the virus to spread throughout the Americas.

QUESTION: Could you comment on the living conditions, perhaps, since a lot of people live without window screens or glass in windows? And also, if you have seen any evidence of West Nile virus in Mexico yet.

DR. PETERSEN: We have not seen evidence of West Nile virus in Mexico yet. Certainly, there's been no evidence in humans or animals that we've been able to detect.

As far as the living conditions go, certainly people who are living in an area where there's a mosquito-borne virus circulating, and they live in conditions where mosquitoes could enter their houses and bite them, would be at increased risk. In fact, there was an outbreak of Dengue, which is a related virus, on the border of the United States and Mexico several years ago. And that very thing happened. Despite the fact that there was more infected mosquitoes on the American side, there was actually more cases of Dengue on the Mexican side of the border.

MS. SWENARSKI: Thank you, everyone, for joining us. That concludes our telebriefing today. As we receive more news, we will keep you updated, and thank you again for joining us.

[End of telebriefing.]

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