CDC Telebriefing Transcript

West Nile Virus in the United States

August 7, 2003

DR. GERBERDING: I'm here today to provide an update on the West Nile Virus outbreak that we are experiencing in the United States and to present you some of the latest facts and figures. But please do keep in mind, as we go forward, that the numbers are starting to change very, very quickly, so you'll need to check our website for the most up-to-date information as we go forward.

We are still working, of course, with our partners in the state and local health agencies to detect cases of West Nile and also to initiate the appropriate public health response. We recognize that the disease is hitting especially hard in some new areas this year, and for the people who are experiencing this for the first time, this is a real tough and difficult situation.

So you have our support, and we of course also are extending our support to the loved ones of the families who have lost people from West Nile or those who are experiencing the difficulties of supporting a loved one who is seriously ill.

The number of West Nile cases in the United States has actually tripled since last week, so we are beginning to see a significant uptick in the number of human individuals affected. So far 153 people are reported with West Nile Virus infection from a total of 16 states. That includes 72 people from Colorado, 19 people from Texas, 15 people from Louisiana, and several people from the remaining 13 states.

We also officially have information about four deaths--two in Texas, one in Alabama and one in Colorado--and we're aware of news reports that may suggest that additional people have died from West Nile Virus infection.

There are some things about the epidemic this year that make it a little bit different from last year. The median age for the people in the diagnosed category this year is 45 years of age, which is actually slightly younger than it was a year ago, where the average age was about 55 years.

And so far this year, all of the cases, all 153 cases of West Nile Virus infection, have been attributable to mosquito bites, so we are not seeing information suggesting that some other mechanism is contributing at this point in time. And keep in mind that we are, of course, screening the blood supply since July for West Nile and pulling any units that are suspicious for infection. So we are doing what we can to protect the blood supply in this country.

Now, I'm going to draw your attention to a couple maps over here, which I think makes some very important points.

First of all, this map here in the center is the picture of states in the United States who reported human West Nile Virus infection and animal West Nile Virus infections as of August 7th, one year ago. So the blue states here, the light-blue states, are those that had reported animal activity only, and the states with the hatches are those that by this point in time last year had reported human cases of West Nile. In fact, they had reported 112 human cases from four states. Louisiana was leading the nation at that point in time with I think a total of over 70 cases.

Now, if you compare that map to the situation that we're in already this year [second map], again, the lightest states here are those that have animal infection only, but in the darker blue states--there are 16 all together--we are reporting human cases.

So what these two maps tell you is that there are more cases already this year with human disease compared to the same time last year. And I think this is one picture of the situation that we are very concerned about, and it tells us that we need to really step up the effort to control mosquitoes and to prevent mosquito bites.

So, to give you some very specific examples here, last year at this time you could see that Colorado had no human cases of West Nile, and actually no West Nile Virus activity at all. Whereas, this year it's leading the country in the number of new cases.

New Mexico had no cases last year and now has two cases of human West Nile Virus infection.

And although Ohio had the most cases last year by the end of the West Nile Virus season, it is also having cases this year, has had a recent increase in the number of cases, suggesting that it's certainly not going to be immune from the problem, and we're very concerned about the fact that there may be more cases on the horizon for a number of the cases that were harder hit last year, not just those states that are new to the map.

All of this is changing very rapidly, and it's important, as I said earlier, to continue to check with our website and to keep posted on the developments as they do emerge over time.

Now, the last graphic I wanted to mention is this graphic over here, which is last year's picture of West Nile Virus infection. And right here, where the red arrow comes down, is where the epidemic curve had evolved by the same time last year. And what you can see is just after the end of the first week of August, there was a huge increase in the number of West Nile cases in our country. In fact, 65 percent of the cases of the entire season occurred in the subsequent six weeks.

So that is very concerning to us. It indicates that we are starting the epidemic with more cases and more areas affected last year, and if the same pattern proves to hold true, we could be seeing an even greater number of affected people.

So the very important message in all of this is the time to take action is now. The time for people to really be conscientious about taking the steps necessary to protect themselves from mosquito bites is right now and to continue those activities throughout the rest of the summer season, and although we haven't reported infection activity yet in the furthest West states in the United States, we certainly don't want to be lulled into any kind a sense that those states would be immune because we know that this mosquito and this virus are on the move and therefore no one can be assumed to be exempt.

Now there are also some warning signs by the surveillance that CDC does in other animal populations.

We know that the reports of West Nile virus infection in horses, for example this year, far outpaces the number of infected horses that we saw last year, and we also have more than twice as many samples of mosquitoes this year showing evidence of infection, and in some areas of the country, in particular, up here in the Northeast, we're seeing just in the last week a significant increase in the mosquito populations that are carrying the virus.

For example last week, in New Jersey, of the various samples of mosquitoes that we tested, we didn't find any, and this week all of the samples came back positive.

So it indicate that this is truly following the seasonal pattern that we saw last year and that people living in these affected areas need to be very aggressive about taking steps to protect themselves.

So let me just review again what those protective measures are because they're very, very important.

It's very important to use an insect repellant that contains DEET. DEET is the chemical that keeps the mosquitoes from being attracted to human skin.

If you see mosquitoes flying around your skin but they're not biting you, it means the DEET is still working and you should be very careful about following the instructions on the device or the product that you're using, to know when you should reapply the DEET and how much you should use.

It's also important to know that you can find very detailed information about insect repellents on the CDC Web site at www.cdc.gov .

There are some things you can do to mosquito-proof your home as well and certainly screens are a very important part of that, but emptying the standing water in your yard, and that includes water in bird baths and flower pots, old tires, Coke cans, whatever you might have laying around on your property, if you eliminate those standing water sources you eliminate the place where mosquitoes breed, and since they don't have a wide range of travel, it will help reduce the mosquito population on your own property.

We're going to be sending out some additional supplemental materials to help spread the word about fighting the bite in local jurisdictions through public service announcements, and so forth.

So as we understand that new jurisdictions are affected, we'll try to provide that updated information and also local health agencies and state health agencies are really a critically important portal of information, particularly as it might pertain to efforts that could be underway in the community to contain mosquitoes or to use larvicides or other sprays to reduce the adult mosquito population.

So as I said, this news that we've presented here today is a reflection of, I think, the complexity and thoroughness of our ability to detect West Nile virus activity across our country, but also gives us a strong message that this problem is certainly not in any better shape this year than it was last year, and in fact the signs indicate that we could be in for a very serious affliction this summer if we don't take steps to educate our public and to get people to really fight the bite.

So thank you for your attention. I'm happy to take some questions.

QUESTION: Dr. Gerberding, I'm John Shurik [ph] with WXIA-TV, Atlanta. As you said, these numbers are changing rapidly.

We understand that Georgia is now reporting a human case of West Nile virus infection. So I guess that would change the number of states to seventeen.

DR. GERBERDING: Let me explain a little bit why sometimes you hear things in the local press that we don't have represented up here on our map. Because this is a part of a national surveillance system and, as many of you know, CDC does not report cases officially until the state health departments have confirmed that they represent true infection, and whenever a new state is involved or when a state has its first cases, we take extra steps in the laboratory to be absolutely sure that it's truly West Nile virus infection and not some other virus that can be confused with it.

So there's often a delay and, you know, we will certainly be adding Georgia to the list, if indeed the test is confirmed to be true.

QUESTION: And to follow up, if I may, to what degree are the increases in numbers attributable to doctors being encouraged to test and report, perhaps milder cases that they might not have tested before?

DR. GERBERDING: Yes, because we do have better tests available to us this year, it is possible that we are making an earlier diagnosis or that we are picking up people who are less seriously ill. Overall, there are two main forms of West Nile virus infection. The encephalitis or the brain inflammation is the form that is the most serious and tends to be most common in older people and is disproportionally included in the people who die from West Nile infection.

But West Nile fever is also an important manifestation, less serious, may not involve hospitalization but can be diagnosed with the same test.

This year, about half of the people with West Nile virus infection that we've reported so far have the encephalitis. Last year, a few more people in the included group had encephalitis, suggesting that we were not picking up as many of the milder forms last year. So there could be some bias in the numbers associated with capacity to pick up milder cases.

But even with that caveat, I think we're still seeing a major increase in West Nile virus activity and it is extremely important that we take all the steps necessary to contain it.

A question here.

QUESTION: April Nelson from CBS 46. Why is this time of year more dangerous than the other months have been this summer?

DR. GERBERDING: There are several factors that influence the biology of West Nile infection and mosquito transmission. Certainly, the climate is a very important component of that. In the winter, it's just simply too cold for mosquitoes to be active in most parts of our country, so they go into a pause state where they're not feeding, they're not breeding, and they're not infecting birds or other mammals.

It's also a process where a cycle in nature gets set up, where mosquitoes are carrying the virus, they infect birds, the virus can multiply in birds and other animals, and then when the next mosquito feeds they pick up an even larger dose of the virus, and so the cycle sort of expands, over time, as the summer progresses, and we're just getting into the season where the right combination of many mosquitoes, large concentrations of virus in the hosts, and people are outside, coming in contact with mosquitoes, all those factors just seem to come together this time of year and create this somewhat predictable pattern.

So we can always anticipate that this will be the season. I think we're hoping that maybe other factors would work against the West Nile virus this year, including perhaps some immunity in some of the species of animals or birds that would serve as hosts. But what we're seeing is that if there is a protective effective from exposure last year, it's certainly not good enough to completely stop the transmission cycle.

QUESTION: Thank you, Dr. Gerberding. Betsy McKay from The Wall Street Journal.

I was wondering if you could explain, once again just clarify these numbers on what percentage of those reported to have West Nile infection have encephalitis and is it proportionally larger than last year, or in absolute numbers larger than last year?

That was one thing and then the other question was what factors may be at play? What hypotheses do you have about why Colorado is reporting so many cases, after having no activity at all last year? Thanks.

DR. GERBERDING: Yes. Last year, about two-thirds of the patients with West Nile infection had encephalitis. This year, at the present time, about one-half of the patients have encephalitis. You know, this is very early, and I would not draw too many conclusions for those numbers because people who have fever today may be diagnosed with encephalitis tomorrow, and so we need to understand, as always with any evolving epidemic, that those patterns my be premature, and we don't have the data yet to draw any firm conclusions about how this will look when it's all played out.

Your second question about why Colorado and why now, I think this is again a pattern that we anticipated based on the movement of West Nile West last year. Although at this time last year, Colorado did not have any evidence of West Nile activity, by the end of the season, there was activity. And so it meant that by the end of the year, some animals, and mosquitoes or birds in Colorado had been exposed to the virus.

And so as bird migration happens and the cycle speeds up, it's not surprising that we would see infection there. And because it's a new state, it may follow the pattern we saw last year, where, for example Louisiana was a new state for West Nile activity, and so they had a particularly difficult summer with a large number of cases.

But as we say often, we cannot look into our crystal ball, and so sometimes these things are better understood in retrospect than they are as we go forward. We can't make any projections yet about who ultimately will have the biggest problem or what states ultimately will have the most number of cases.

Let me take a question from the phone, please.

OPERATOR: And for those on the phone, a quick reminder, if you do have a question, please press star one.

And we'll go to the line of Miriam Falco with CNN. Please go ahead.

QUESTION: Hi, Dr. Gerberding. Thanks for having this.

My question is a little bit similar to what was just asked. Do you think the fact that there are 72 cases in Colorado now is part of this cycle; the fact that there were some mosquitoes in Colorado last year, and thus it's easier to spread? And what predictions, without having the crystal ball, do you see for the states like Illinois and Ohio that were hardest hit last year?

And what information can you provide to the states that's different from what was disseminated last year? Are there new PSAs? I mean, essentially the information would be the same as you were giving out last year, would it not?

DR. GERBERDING: Yes. Again, I can't predict what will happen in Colorado as the season unfolds, nor can I completely explain it this time why they are seeing the largest number of new cases. Of course, any reported illness is dependent on the actual frequency of the illness, stability of clinicians to diagnose the illness and the sensitivity of the reporting system. And we know that the efforts that have been in place for several years now, to enhance all of those capacities in the states, do seem to have paid off. So we are seeing very good reporting of West Nile infection.

The advice on how to protect yourself against West Nile Virus infection hasn't changed from year-to-year. We are very vigorous in recommending that people take the steps necessary to reduce mosquito bites and to reduce mosquito breeding on their property, but we don't have any new tools in our took kit to help protect people.
What we do have new this year is some very important advance in the field of the diagnostic testing, and particularly in our ability to protect the blood supply, and in addition the work that the NIH has moved forward in terms of developing a vaccine for West Nile, but we're not going to have a vaccine in time to make any difference this year. So it's the old-fashioned method of reducing mosquitoes and reducing mosquito bites that we have to rely on.

Let me take another question from the phone, please.

OPERATOR: And that will be from James Erickson, Rocky Mountain News. Please go ahead.

QUESTION: Hi. When I ask health officials out here why we're seeing so much West Nile activity in Colorado, I get two answers. The first is that this is the second year the virus has been in the state, and West Nile often hits hard the second year. You've already alluded to that.

The other answer I get is that the rainstorms here have been ideally timed this spring and summer to produce lots of mosquitoes.

I'm wondering what other factors could be contributing to this outburst. For example, is this telling us something about the competence of Culex tarsalis as a vector for West Nile?

DR. GERBERDING: One of the unfortunate aspects about the West Nile Virus is that it's not very picky about its host. It affects an extremely broad range of birds, it affects an extremely broad range of mammals, and it affects an extremely broad range of mosquitoes. So while it may have a particular favorite mosquito host in a given geography, it's not picky, and that's one of the reasons why I think, at least one of the hypotheses about why it's been able to spread so quickly across the United States, because it can enter a whole variety of hosts and mosquito vectors.
Therefore, something that caused a reduction or a downturn in one population, doesn't have much impact on the overall life cycle of the mosquito.

But you do bring up an important issue, and that is the issue of weather. We know that climate is an additional variable that has a big impact on bird migration patterns, as well as mosquito breeding, and so it is certainly possible that in a particularly rainy season or where there is a great deal of water standing that allows more mosquito breeding, that would be a worse year for mosquito populations and all of the mosquito-borne diseases.

Let me take another question from the room.

QUESTION: Thanks, Dr. Gerberding. David [inaudible] with Fox News Channel.

What do you make of the reduction in the median age of those affected this year compared to last?

DR. GERBERDING: It's too early to draw any conclusions about the age distribution overall. One factor that might be accounting for that is the fact that we are including people with less-severe disease in a slightly greater proportion this year than last year. And because the older you are, the more likely you are to get the encephalitis form of West Nile Virus infection, if we're picking up less serious disease, then we may be picking up more disease in younger people, and that's changing the distribution a bit.

But, again, we have people of all age groups represented in the epidemic so far, and we can't conclude that anybody is immune from even the most severe form of infection.

I would just add to that that because it is the elderly population that is at the highest risk for the encephalitis, it's especially important that our seniors take the steps necessary to repel mosquitoes or to wear long-sleeve clothing and long pants when outdoors because this could be an especially serious medical issue for you.

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

OPERATOR: And that's from Elizabeth Kaledin, CBS News. Please go ahead.

QUESTION: Hi, Dr. Gerberding.

I'm sort of wondering about the efficacy of the prevention program that we have in place here. You know, you came out last summer full throttle with this Fight the Bite program, and I'm not sure how well that was broadcast in Colorado, but even in the face of this strong prevention plan, we've got this huge outbreak in Colorado, and we're asking people in the summer to wear long-sleeve clothing and long-sleeve pants. Is it really working, and is there anything else you're working on in its place that might be more effective?

DR. GERBERDING: Preventing West Nile Virus infection is a multifactorial process, and of course mosquito control is a huge component of that. One of the reasons why we make these investments in tracking the mosquito or the virus in mosquitoes, and birds, and animals is so that we can anticipate where the next human cases will be. And when a jurisdiction knows that it has the virus in that area, then there are additional steps that officials may need to take that help reduce the threat to human health. And those steps include using larvicides to kill mosquitoes as they are hatching in the breeding ground, as well as, in some cases, if the problem can't be controlled that way, decisions about spraying for adult mosquitoes may need to be considered.

So it's a comprehensive process. But no matter what your jurisdiction is doing or is able to do or what makes sense to do in a particular location, there's always a role for personal protection.

You've asked is it enough and is it making a difference. It's kind of the dilemma of all prevention activities, is that it's very difficult to show what you've prevented. You can only show what's left over after all of your prevention impact has been accounted for.

So I believe that the information we have so far indicates that a comprehensive vector control program is a very important strategy and is important in reducing mosquito populations and reducing risk, but in addition, we know that mosquito repellents work, and the other measures to reduce the possibility of a bite are very, very important.

So we don't want people to think, oh, well, it's not making a difference. If anything, this is an indication to step up to do those things even more rigorously before, and not to forget that the West Nile season goes on for a long time. Last year it went clear through October. So it's not just a question of when it's summer vacation. It's a question for the summer and the fall.

A question here.

QUESTION: I'm Daniel Yee with Associated Press.

So what are the challenges this year for dealing with a virus that's here to stay?

And, secondly, have you had any requests from states for CDC assistance?

DR. GERBERDING: The challenges this year are really the same as the challenges every year, and that is anticipate where the problem is going to emerge, act proactively in those jurisdictions to do the appropriate things to reduce the threat to human health, to do everything possible to protect the blood supply, to inform people. Clearly, the more you know about protection, the better of you are, in terms of making personal health decisions for you or your family.

CDC has already provided to the states a great deal of funding to support West Nile prevention activities. It's been an ongoing program, we scaled it up last year and we're continuing to do everything we can, not only to provide money to state and local health agencies but also to track the problem and to make this whole ARBONET, this is called, our surveillance system, to make it as useful and as timely as we can to people in those jurisdictions.

If you're interested in specific dollar amount for our funding, we can make that information available to you through our press office.

QUESTION: I guess there've just been Epi teams and stuff?

DR. GERBERDING: Yeah. So far, we have not received requests for specific Epi aids on behalf of West Nile. I will say that in Colorado, one of our large CDC components if physically located in Fort Collins, Colorado, and that happens to be our division that deals with West Nile virus infection. So there is actually a great deal of interaction with CDC in Colorado and the state and local health officials there, so it is not a sign of anything other than so far, the states are well-prepared and are able to manage the situation without additional technical support from CDC.

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

MODERATOR: And that's from Karen Mellon [ph], Chicago Tribune. Please go ahead.

QUESTION: Yes; hi. Last year, it seemed that most of the cases, especially in Illinois and other parts of the Midwest, were clustered in urban/suburban areas. I can't see your maps but I'm wondering, with cases being reported this year, is that following a similar trend?

DR. GERBERDING: I believe your question was are we seeing a tendency toward more cases in urban and suburban areas?

QUESTION: Yes--

DR. GERBERDING: Was that your question?

QUESTION: [inaudible].

DR. GERBERDING: Yes. We actually track the affected counties that are reporting West Nile virus activity and there always is a tendency to see more human cases in the areas that have a greater density of population, so that's one of the explanations for that distribution.

But the rural areas are certainly not immune, as we've seen in the animal populations and in some of the human people who have been affected in other parts of the country this year, so it's too soon to tell what the overall distribution will be as this moves forward.

Do I have another question from the phone, please.

MODERATOR: And that's Rob Stein, Washington Post. Please go ahead.

QUESTION: Yeah. Hi, Dr. Gerberding. Thanks for doing this. You might have had these numbers on the slide that you showed but I couldn't see them over the phone. I was just wondering if you had the equivalent numbers for this time last year, how many cases, how many human cases, how many deaths, and how many states were affected this time last year?

DR. GERBERDING: Yes. Last year, at this time, we had a total of 112 cases in four states. This year, we have 153 human cases in 16 states, and if you want additional breakdown in terms of reported deaths and what those states were, we'll be happy to provide them to you, so you can just get in touch with the CDC press office.

I'll take another telephone question, please.

MODERATOR: And that's from Anita Manning, USA Today. Please go ahead.

QUESTION: Hi, Dr. Gerberding; thank you for doing this.

I have a couple of sort of unrelated questions. One of them is you mentioned that the blood supply is being screened and has been since early July, and I'm wondering how often West Nile virus is being picked up in donated blood?

And then I also wanted to ask if there's anything different about the mosquitoes that are out West, that's causing the locus of this epidemic to move West as it has been?

DR. GERBERDING: The blood supply is being screened for West Nile virus infection using a test that was created very quickly and represents, I think, a heroic achievement on the part of the blood banking industry as well as the FDA to get this out in such a short period of time.

The test is very sensitive and that means that it will detect many cases of possible West Nile virus infection that may not actually represent true infection.

But that's exactly the way we want it to work. If there is the positive screening test in the blood, those units of blood product are immediately pulled so that they don't get transfused into people, and then we take our time sorting out whether they represent true infections and whether the unit actually had live virus in it or not.

So there have been units of blood pulled. We reported, some time ago, the first confirmed unit of blood that was pulled from the blood supply and what we're doing right now is carefully evaluating the pulled units to see whether or not they would have posed a threat if they had been transfused, and we're looking to see whether or not that information about pulled units is an additional marker of where the virus activity is, that would help us understand even better where a threat to human health resides.

So we will be providing you updated information as the full assessment of the pulled units of blood gets completed.

Is there another question from here in the room?

If not, let me just go to the phone again.

MODERATOR: Again we'll go to John Lauerman, Bloomberg News. Please go ahead.

QUESTION: Is there any sense--thanks for doing this, by the way. Is there any sense of how effective the tests are? Do we have any more information about that, the Roche and Chiron test?

DR. GERBERDING: The tests are very good, again, at screening for West Nile virus infection but the definitive test is something I believe called the plaque neutralization assay which really takes a while to complete.

Am I right in that? Did I get that terminology correct?

That is a test that really relies on the virus to actually grow up and to be definitively distinguished from other viral agents that it can be confused with.

So the gold standard test is still a test that is done primarily by CDC in Fort Collins, and we don't have to use that gold standard test all of the time because once we know that the virus is in the jurisdiction, if the screening test is positive and the patient's clinical signs and symptoms are compatible with West Nile, the commercially available tests tend to perform extremely well.

But we will be looking at that as we go forward this year and really being able to conduct a much more thorough assessment of the reliability of the new tests that are being used for diagnostic purposes.

In cases where there's a discrepancy between the screening test in a commercial laboratory, we always encourage that the test be reevaluated by the state health department laboratory and then referred to CDC, if necessary, to clear that up.

Let me just take one more question from the phone, please.

Is there one more question from the phone?

MODERATOR: Yes, from the line of Paul O'Niece [ph] with WCBS-TV. Please go ahead.

QUESTION: Dr. Gerberding, thank you for taking our questions.

A point of clarification here. You mentioned this rapid test used for blood. A rapid test is also being used for human cases; is that correct?

DR. GERBERDING: That's correct.

QUESTION: Now how is the rapid test affecting the numbers that we're talking about? Is it possible that we're seeing more numbers, this 153, because the tests results are coming back faster?

DR. GERBERDING: No. The number of cases here cannot be related totally to the speed of the testing, although we are likely to be able to rule in cases more quickly than we were in the past.

The testing of the blood is not something that's reflected in the case count here. That would be a separate surveillance system.

Finding the virus in the blood of a blood donor does not meet the case definition for West Nile virus infection. So that's why we are counting those separately.

So these numbers are not inflated for individuals that could be picked up by screening the blood supply. But, again, these numbers are going to change over time.

We want you to be aware of the fact that while we expect, unfortunately, we'll be seeing more cases of West Nile, that we are constantly evaluating the performance of the test, and beginning to understand the broader clinical picture of this illness, and we certainly will anticipate updated information and a more accurate view of the scope and magnitude of the problem as we go forward.

The bottom line is that it's here, it's happening in a lot of jurisdictions, every sign indicates that it's on the increase and now is the time for people to step up their efforts to fight the bite.

Thank you very much.

Listen to the telebriefing

Media Home Page | Accessibility | Privacy Policy | Contact Us
CDC Home | Search | Health Topics A-Z

This page last updated August 7, 2003
URL: http://www.cdc.gov/media/transcripts/t030807.htm

United States Department of Health and Human Services
Centers for Disease Control and Prevention
Office of Communication
Division of Media Relations