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CDC Telebriefing Transcript

West Nile Virus activity in the United States, Measles Outbreak in the Marshall Islands and Preparing for Hurricane Isabel

September 18, 2003

DR. GERBERDING: Good afternoon. Welcome to our news conference.

I'm going to be covering three topics today: first of all, the update on the Department of Health and Human Services and CDC response to the hurricane; second, some updated information on West Nile, particularly as it pertains to blood transfusion and blood safety; then, thirdly, a very brief update on a measles outbreak investigation that's ongoing in the Marshall Islands. So, there are three very important public health issues to provide you some perspective on.

Secretary Thompson has made the full resources of the Department of Health and Human Services available to support the public health response to Hurricane Isabel. The Operations Center in Washington, the Secretary's Command Center, is collaborating with FEMA and the other federal agencies. CDC's Command Center is in reactive mode to respond to any request for assistance relevant to some of the public health complications that we know from prior experience have complicated hurricanes.

In the last hundred years, we've had a number of hurricanes. As you know, these hurricanes can be deadly. We've actually sustained more than 14,000 deaths in the United States from hurricanes during that time frame, and many, many more injuries and serious loss of life. So, it is very important that people know what to do and follow the instructions from the local emergency managers who really are in the best position to advise about local issues. But, we also have a number of resources that are available to people who have questions.

Specifically, I would refer you to our website,, where we have a great deal of information under the subtopic of hurricanes that is pretty easy to find.

This information helps people know what to prepare for in advance of a hurricane, but also very importantly provides guidance on what to do after the hurricane. Many injuries and accidents occur when people return to their homes, particularly electrical injuries from groundwater, electrical lines that have come down, as well as gas and fire issues, including carbon monoxide poisoning. The information provides some very important health tips about post-hurricane management and safety as well as what to do to prepare and what kinds of supplies and preparations people need to be making.

CDC has also deployed about 20 personnel to assist state and local health officials up and down the Eastern seaboard. CDC staff are on-site to provide a variety of technical assistance around things like water safety and the other issues in emergency management. For people who need more information and can't or don't have access to the Internet, there are hotline numbers that are available for the public. I'm going to give you a couple numbers here, just general information for the public, at 888-246-2675. That information is also available in Spanish at 888-246-2857. And for clinicians who may be treating injured people or who are worried about treating injured people, the hotline is 877-554-4625, and this information is available TTY at 866-874-2646, and those numbers will be available to you after the press briefing if you didn't catch that on the fly.

Now let talk for a few moments about some of the updates relevant to West Nile virus infection. As you know, we are still in West Nile virus season. Although we may be past the peak of the epidemic in most areas of the country, there are several states that have reported large numbers of cases, particularly Colorado, with more than 1,500 cases of West Nile, South Dakota with 580, Nebraska with 554, Wyoming with 282, and Texas with 276. Although the news may be reporting that we're past the peak, it's certainly not over yet, and people still need to take the steps to protect themselves, which, of course, as always, includes using DEET mosquito repellent, wearing clothing that covers the arms and legs, and emptying the standing water that's in their environment.

Now, this year, one of the major changes in the epidemic has been the access to the West Nile virus test, and this is allowing two things to happen: First of all, people with West Nile fever and mild symptoms are being diagnosed more often, so we do have more cases of West Nile fever than we did last year. But we have about the same number--in fact, we actually have more cases of encephalitis this year than we did last year. So, we can't say that the epidemic is not as bad as it was last year and that we are seeing an artifact of testing. In fact, the indications are that this was also a very--very difficult year for West Nile, particularly with people in jurisdictions that are being hit by this for the first time. And we know that it's a difficult and frightening situation.

The FDA has moved incredibly quick to make testing available that will allow us to do a better job in clinical diagnosis, but also important, in making sure that the blood supply is safe. Released today, by the New England Journal of Medicine, are some reports of transfusion-associated West Nile virus infection from last year, which is when we first recognized that this infection could be transmitted through blood products. There were several investigations that were conducted, and the upshot of all of that work last summer was that we recognized how important it would be to have a better way to screen the blood supply beyond just asking donors for symptoms of West Nile virus infection.

FDA, working with CDC and a private manufacturer, was able to get a West Nile virus test in an unprecedented period of time. The tests are based on the detection of nucleic acid or part of the genes of the virus. They're very, very sensitive, and we've been using them across the United States since late June, early July, so we are screening blood donors for West Nile virus infection. And we've had a great deal of success with that. Overall, this nucleic acid test has identified more than 600 infected units of blood, which were, of course, pulled from the blood supply and not used for transfusion. However, because this is a brand new test, and it takes a while for the blood-banking industry to be able to scale up and do it quickly enough to effectively screen all units, the testing protocol involves pooling samples of blood from several donors and then testing the pool sample. So it's somewhere between 6 or 16 donors' blood mixed together and the test is run on that mixed pool.

If the pool is found to be positive, the individual donors are then evaluated and that blood is not used for transfusion.

We are working with a large component of the blood-banking industry and one of the entities involved in blood banking did a special study of the pool testing protocol. They went back and tested all the individual donors to see whether or not they could pick something up on a single sample that was being diluted out when pooled. They found that on very rare occasions the virus concentration was too low to be picked up when the samples were mixed, but when tested individually they could find some virus.

So that's why we've been saying all along that this is a major step forward in protecting the blood supply but it's not perfect, and clinicians and public health officials need to be on the lookout for cases of fever and headache and encephalitis in blood donor recipients--blood transfusion recipients to that we can look back and make sure that an infected unit doesn't slip through the cracks.

We reported today in a MMWR Dispatch, two cases of transfusion associated West Nile virus infection. The first case was related to a unit of blood slipping through the pooled donor protocol, and the other investigation is a little less clear. We're not exactly sure which units went to the transfusion in the second case because the patient received some blood products that were donated prior to the point where we had the test. So the donations were made in February, the products were stored. They were transfused more recently, so it's a little bit more complicated to figure out.

But the bottom line is these two individuals have all of the clinical criteria of transfusion-associated West Nile virus infection characterized by encephalitis. Thankfully, both of these individuals are recovering from the encephalitis. One of them was recognized as a part of this look-back investigation, and the other was recognized because the clinicians did the right thing. The clinicians recognized that following the transfusion the patient had presented an illness that could have been West Nile virus infection, and so they did the special studies.

I think the take-home message here is that our transfusion supply is far safer than it was a year ago, thanks to the incredible work of the FDA and all of our colleagues in the blood-banking industry, but we are still on the look out for an occasional case that could slip through. The risk is a very low, but not a zero risk. Certainly, if people are advised to receive a blood transfusion by their clinician, it's important that they receive the transfusion since very often these are life-saving transfusions. The risk of West Nile, although not zero, is generally not large enough to contraindicate the transfusion.

I'll finish with just a couple of words about a very important outbreak of measles that CDC has been involved in. This is an outbreak that has been going on in the Marshall Islands out in the Pacific Rim Area.

So far, we have clinically diagnosed 647 cases of measles among people who live in this area. These are sometimes very serious cases including 58 people who required hospitalization and three people who have died from measles.

Now, you might ask why there was a measles outbreak when we have a very effective vaccine that prevents measles when used properly. Sadly, in this particular area of the country, vaccine coverage was not adequate to protect the population. So, when the measles was introduced from parts of Asia where there have been continuous outbreaks of measles, it spread very quickly through the population in this community. It infected not only just children but adults of a broad age range. Some of these people developed very, very severe measles illness.

This experience has some very important lessons for us here in the United States. First of all, we have to continue to be vigilant about making sure that people understand the importance of measles vaccine coverage everywhere in the world. Second, it tells us what happens if there is a reduction in the coverage. We know that the goal is to have a measles completely prevented through this life-saving vaccine, and in this particular population, the estimates of coverage were quite low. Somewhere less than 75 percent of the children who should have been vaccinated actually had received the appropriate immunization schedule.

What we are recommending is that people in all communities receive measles vaccine. In this country we use the recommendations issued by the Advisory Committee on Immunization Practices, which recommends that all children receive measles vaccine at the age of 2 to 15 months, and that there's a repeat immunization before they start school so that they have maximal immunity. This recommendation provides an excellent degree of protection. If a child does not receive the second dose of measles vaccine, their protection is limited, and they could be vulnerable if we had an introduction of measles into this country, which occasionally does happen.

We are faced with a public health situation, and CDC is working hard with the health officials in the Marshall Islands to get this outbreak under control. We have delivered thousands doses of vaccine including part of the supply of measles vaccine that we sustain in the National Pharmaceutical Stockpile for this purpose. We also have had several CDC staff go to the Marshall Islands and assist with the door-to-door vaccination campaign that's going on there. And I'm pleased to say that at this point we believe we have achieved a better than 98 percent coverage of the susceptible population in that community. We expect now to see cases decline, and at least in that particular area the situation is under control.

The bottom line is that measles is still a very real and important global health problem, and we have to work hard as part of the global community to get this outbreak situation under control and also to continue to sustain our investment in immunization here in this country.

So let me stop and take a few questions. I did want to mention that Dr. Jesse Goodman from the U.S. Food and Drug Administration, who's the Director of FDA's Center for Biologics Evaluation and Research, is on the line. So if there are any detailed questions about the blood supply or blood testing, I may defer them to Dr. Goodman.

So let me take the first question from someone here in the room.

QUESTION: Dr. Gerberding, thanks for doing this. Diana Davis from WSB in Atlanta. If someone is--does have their blood test positive for West Nile, after they're clear of the symptoms of the illness, does their blood clear or are they forever not donors? What's the situation with that?

DR. GERBERDING: The way we are testing the blood right now, we're testing for the actual virus nucleic acid, so once the individual has cleared the nucleic acid from their blood, they would no longer be infectious. And we don't have enough experience with this test over the long run to know how long people would remain test positive under this particular donation regimen.

So the basis of the testing is to screen out the people with the virus in their blood.

QUESTION: Betsy McKay from the Wall Street Journal. Can you give us a sense of the timing when you think it would be possible that individual units will be [inaudible] blood supply so that the problem with the occasional misses?

DR. GERBERDING: Thank you. We are recommending in today's MMWR that in areas where it is feasible to do individual donor testing, that that be done, and, in fact, several states are already doing that. I can provide you with a list of the areas where that's going on already. Many of the blood suppliers are able to test individual donor units. But it's not possible for us to do that at every blood donation center around the country right now simply because the test kits are not as available, and the time it takes to do this could result in some changes in access to the blood supply.

So we will get there, but at the moment this is the best compromise. And where they are doing individual donor testing are in the areas that have the highest risk of West Nile infection, as you might expect, so we're taking steps to make sure that we have the most sensitive test we possibly can, and I'm sure the FDA—Dr.Goodman, correct me if I'm wrong, but I'm sure the FDA is working on developing an even more sensitive test. So we've made such progress, but there's always one more thing you can do, and we're all committed to keeping the blood supply as safe as we possibly can.

A question here?

QUESTION: Dr. Gerberding, Dennis O'Hare from WXIA-TV in Atlanta. You mentioned when you were talking about Hurricane Isabel the possibility after the hurricane, accidents and injuries. Are there any disease concerns that come up after a hurricane like this or supply problems or anything like that? And what is CDC [inaudible] to prevent those [inaudible]?

DR. GERBERDING: Well, one of the main issues is, of course, water quality, and FEMA and the other management agencies will place a high priority on restoring power, utilities, and water supply. But another very important concern for individuals in their homes is food safety, because if you've lost refrigeration and the capacity to properly store your food, then issues of spoilage are a problem. We have some tips for people on food safety issues on our web site, and the local health officials are making that information available to their citizens as well. That will be one of the areas that CDC will contribute some technical advice to.

I'll take a question from the phone, maybe from the Denver Post.

OPERATOR: Thank you. Deidre Henderson, your line is now open.

QUESTION: Thank you for doing this. Dr. Nakashi's (ph) presentation today indicates an estimated 75 percent of West Nile-tainted blood has been intercepted by the nucleic acid test. Is that a reasonable percentage for a first-generation test? And I have a second question.

DR. GERBERDING: I think we need to do more research before we know exactly how sensitive and successful this test has been. But that's an extraordinary achievement for a first-generation test. I think one of the reasons that we were able to do this so quickly is because the blood banking industry already had experience with nucleic acid testing. This is the way we screen for hepatitis C virus and HIV infection and some other viruses. Therefore, the infrastructure to do the testing and the training in the methodology was already something that people were familiar with, so they were able to act very quickly to make our blood supply as safe as we possibly could get it with the technology we have available today. And this really is a remarkable achievement.

QUESTION: And a second question--

DR. GERBERDING: --a question from the phone. I think I have someone from Knight Ridder on the phone.

OPERATOR: Thank you. Seth Bornstein, your line is now open.

QUESTION: Dr. Gerberding, thanks for doing this. In terms of the--going back to the hurricane, and combining it with West Nile, is the experience with hurricanes in '99, is there--because we have such an increase in standing water after a hurricane, how much of a--do you expect an increase in West Nile post-hurricane? And, also, in terms of the waterborne diseases, are you mostly thinking about cryptosporidium, or what waterborne diseases are you most worried about?

DR. GERBERDING: There are many infectious diseases that are problems when the water supply is interrupted, and so certainly the bacterial infections that could be washed into the water system from effluents from farms and so forth would be the highest concern if the sanitation of the water cannot be secured. Cryptosporidiosis has been a problem after flooding and other natural disasters, so certainly that would be something that could be of concern and one of the reasons that we have the technical experts on-site from that particular content area.

With respect to West Nile, anything that increases standing water would, of course, increase the tendency for mosquitoes to breed and potentially spread West Nile infection. But the other factors that play into that are, of course, the temperature, the weather, and a lot of other follow-up scenarios. It is really impossible to predict what impact the hurricane will have on West Nile. But I think we all recognize that even though the urgent imperative is the post-hurricane or the events immediately afterward, we will need to remind people not to forget about West Nile virus infection in that context and to stay vigilant for that, too.

Dr. GERBERDING: A question here in the room.

QUESTION: Yeah, hi. David Walburg from the Atlanta Journal Constitution. I was just wondering regarding the West Nile transmission through transfusion, we've had two so far this year. Do we know how many we had last year at this point?

DR. GERBERDING: I can't tell you exactly at this point in time. The report in the New England Journal of Medicine is describing, I think, 23 individuals with transfusion-associated West Nile virus.

Dr. Goodman, do you know where we were at this time last year with transfusion-associated cases? Dr. Goodman? Are you on the line?

[No response.]

DR. GERBERDING: Let me get back to you on that one. We have that information, and we can make it available to you.

OPERATOR: Dr. Gerberding? Excuse me, please. Dr. Goodman's line is now open.

DR. GERBERDING: Okay. Thank you.

DR. GOODMAN: Yeah, I think that's a difficult comparison. I think, you know, last year we were just becoming aware of a problem. The kind of surveillance systems we have in place this year that are extremely active and aggressive weren't there. I think even so we were aware of more cases last year, you know, probably on the order of half a dozen at this time. But I think last year there were many, many cases that either didn't meet case definitions or probably went unreported, whereas this year we have a very aggressive 50-state system in place.

The other point I wanted to make is that we do know, as Dr. Gerberding said earlier in the presentation, that already over 600 units of blood were detected that are potentially infectious with significant levels of virus in them. These were removed from the blood supply, not transfused, and since these units routinely go to something like on the order of almost two recipients per unit, you know, we can presume that we've prevented a very large number of infections and some significant amount of clinical disease.

This year we should certainly obtain a lot more information with all the blood being tested. We are continuing studies to determine for these very low level units that may not be detected by the current testing that's out there what the risk of infection is. It is unfortunate that we have two apparent cases that may have been at such low levels that they weren't detected and then may have transmitted the disease, but again, we have to keep that in perspective of a year ago from now. A year ago, we had no testing and the remarkable effort of putting this testing into place in this time to improve blood safety from West Nile virus.

DR. GERBERDING: Just to follow up on where the testing of the individual donor is going on right now, at collected blood banks in Kansas, Nebraska and North Dakota, Oklahoma and South Dakota--and there may be others--that are using a methodology that may increase the sensitivity of the screen. We are doing everything we can.

DR. GOODMAN: Right. And another thing is that it may also be possible to improve the sensitivity further of some of the currently used assays. So we're looking at everything feasible, both to figure out how sensitive the current assays are going to be and then, where needed, to improve them. But this is currently running absolute maximal capacity for the blood banks, et cetera, to do the testing they are and to target, as Dr. Gerberding said, any excess capacity for single donor testing into the areas where the risk might be significant.

DR. GERBERDING: Thank you, Dr. Goodman.

Let me take a question from Betsy Bates at Internal Medicine. Betsy, are you on the line?

OPERATOR: Thank you. Betsy Bates, your line is now open.

MS. BATES: Hello. Thanks very much for doing this. I wanted to ask a little bit more about the epidemiology of West Nile this year as compared to last year. You had mentioned in passing that there was a little bit more encephalitis this year. I also wondered what the pediatric case count looks like this year and how many cases we have of acute flaccid paralysis.

DR. GERBERDING: Thank you. I would like to give you a very simple answer to your question, but I have to provide some more complicated context.

This year we have two major differences in surveillance capacity. One is that we have a clinical test widely available so that people with mild forms of the disease are being picked up and reported, and because of that technology advancement, we are also diagnosing cases earlier than we were last year. So our reporting system is not calibrated the same way which makes the direct comparison from last year to this year.

When we segregate cases, just looking at those who are classified as meningitis or meningo-encephalitis, then the epidemic curves look very similar, but we're still seeing more people so far this year as compared to the same time last year. Whether or not when we adjust for the time lag of reporting that will equal out eventually is too soon to tell. So, I don't want to draw any firm conclusions about this year versus last year until we have all the data in and we can really get the full picture accurately.

That's a very important question about pediatric illness and we can identify that information for you and respond later. I don't have it off the top of my head here today.

With respect to the paralysis illness, we are doing a prospective assessment of cases coming into hospitals in some of the hardest hit areas to try to understand the full spectrum of neurologic diseases associated with this. Again, that evaluation is in progress and we won't have information until we've gotten all the neurologic reports compiled. I think that's of great interest to everyone because, as you recall, last year was the first year we recognized that there was a broad spectrum of neurologic disease beyond meningo-encephalitis associated with West Nile, including very rarely a disease that looks very much like polio.

MS. BATES: Thank you.

DR. GERBERDING: Do we have another question from here in the room?

QUESTION: Daniel Yee with the Associated Press.

Can you tell me what the relationship is between the U.S. and the Marshall Islands as far as--Do they get federal help for research under the Free Association Compact and how large has measles outbreaks in recent U.S. history been? I mean, how long has this been?

DR. GERBERDING: Thank you.

Let me ask Dr. Orenstein to answer the second part of your question because he's our expert here on measles and has an historical view of previous outbreaks in the U.S.

We do have some responsibility for health services in the Marshall Islands. We supply the vaccine to the Marshall Islands and we have a great deal of responsibility for the immunization program there. So this is something that we consider to be part of our jurisdiction and we will be working to identify why the immunization coverage is less than ideal.

One thing to appreciate about the Marshall Islands is that they don't have the same kind of information systems that we have here and it's been very difficult to track school age children and make sure that they're getting that second dose of immunization. The recordkeeping and identifying and tracking people in a population that doesn't have the same mechanisms for census that we do makes the identification of lower than expected coverage complicated.

Let me ask Dr. Orenstein to address your other question about the severity of past measles epidemics.

DR. ORENSTEIN: My name is Walt Orenstein, O-r-e-n-s-t-e-i-n. I'm Director of the National Immunization Program at the CDC.

The United States in the last several years has generally had a hundred cases or fewer. In 2002, we had about 44 cases. In 2000, we retained a group of experts who thought that measles was no longer circulating in the United States.

However, we do have about 30 importations of measles a year, and we have had importations of measles with five spread cases into Hawaii. We've had importations from the Marshall Islands, a spead case aboard an airplane in a California residence, so that the threat is there if we don't keep our immunization coverage up.

DR. GERBERDING: I would just say that Dr. Orenstein has just returned from the Marshall Islands, so he has first-hand experience about the situation there.

Do I have a call from Mr. Vole [phonetic] from the South Dakota Public Broadcast System?

OPERATOR: Thank you. Brian Vole, your line is now open.

MR. VOLE: Thank you very much. This is Brian. Can you hear me all right?

DR. GERBERDING: Yes, we can.

MR. VOLE: There has been a high incidence of West Nile virus tracked through many travel communities. Here in South Dakota we have eight and a half percent of the population is Native American. There seems to be a pretty high, significant rate among Native Americans.

I was wondering if the CDC had any comments as to why these communities seem to be vulnerable to the West Nile virus.

DR. GERBERDING: There are a lot of factors that play into community vulnerability in any epidemic, and in this case, Native Americans--and I'm very familiar with the situation in some of the geographic regions in South Dakota where this has been a problem. People spend more time outdoors and so they have more opportunities to be exposed. But also, the geographic configuration, particularly in western South Dakota, in the Cheyenne River and other river valleys where the mosquitoes are particularly breeding, bring people in close proximity to the source of the mosquito. There is a geographic factor as well as a human cultural factor that can increase risk.

One of the things we're concerned about at CDC is the adequacy of our communication strategies to be relevant to people in all communities. We do have a close working relationship from someone in South Dakota who has been translating our public messages into context and channels that would be relevant to people in the Native American population.

We know that in any community there is often a gap between what people know and what people do. Today's MMWR also describes some of the information from Connecticut last year, where most people had a good understanding that people were at risk for West Nile, particularly elderly people were at risk for the complications of West Nile, but many fewer people actually took the precautions necessary to protect themselves, even when they knew or believed they were at risk. So fixing that gap between what people know and what they do is one part, and the other gap is making sure that we and our partners in State and local health agencies communicate effectively so that our information has relevance to people in all communities.

MR. VOLE: When you talk about communicating to these communities, do you mean speaking Lakota?

DR. GERBERDING: I don't think we would go as far as that, but certainly, if there are people who need to communicate in that language and are available to help translate health messages into Lakota, that would be a strategy at the local level that we would support if it was needed. I'm speaking also, just framing things in terms that are locally relevant. You know, sometimes, believe it or not, the Federal Government is not the trusted source of information, and we know that in many communities there are local experts or peers or tribal leaders or trusted clinicians that are much better at communicating with people in day-to-day terminology that they have an experience with and that they trust, and they're more likely to accept information from those resources.

We need the whole chain of communication to be effective from the scientists to the communications staff, all the way down to the most credible resources that we can find at the local level to help people understand what they need to do to protect themselves.

Can I have another question from the phone, please?

OPERATOR: Thank you. Your next question comes from Lisa Gough [ph].

QUESTION: Hi. Thank you for taking my question. I have a question regarding the hurricane situation. Would you please detail the types of injuries that people may incur from hurricane situations besides the foodborne illnesses and the water issues?

DR. GERBERDING: Let me again refer you to our web site because we have some additional key facts about hurricane readiness on the CDC’s web site.

Some of the areas that are most important, as I mentioned, are food safety because of problems and interruptions in the food cold chain, if you will, particularly concerned about dairy products, milk products, eggs and so forth, where there's opportunity for the temperature to rise and the bacteria in those two substances to incubate and then cause disease upon injection. That's also a problem, obviously, for meats and things that are--would be considered leftovers in the refrigerator.

In areas where there's concern about water safety, boiling is the most important aspect of prevention after the fact, and there are other things that can be done in extreme cases. If you can't boil the water, a few drops of household bleach will render most bacteria inactive and so forth.

But the real issue where injury prevention--these recommendations come from our National Institute of Occupational Safety and Health--pertain to the kinds of dangers that occur when you go back into an area that's been damaged by wind or water. In particular, NIOSH recommends that people do wear protective clothing, hard-toed boots, outer garments that cover their skin effectively. In some cases head protection is very, very important, because there are several hazards.

With electrical hazards people are advised to turn off the power at the main circuit breaker if there's been water anywhere in the context of the electrical system, to not enter flooded areas or touch electrical equipment if the ground is wet. Never, of course, handle a downed power line or something that might be a downed power line. If you're using a gasoline or diesel generator, which very often people do when the power is off, to switch the main breaker fuse on the service panel to the off position before you start the generator because there are hazards associated with not doing that. And that if you have to do something that's near a downed power line to be sure to contact the utility company before you go in and put yourself at risk in that situation.

One other important hazard is the carbon monoxide hazard associated with using generators or other diesel-powered equipment in confined areas. And it's very important that people follow the manufacturer's advice about the safe use of those generators, and do them in environments that are well ventilated.

One of the most common injuries after a hurricane is very simple. People go in to move bulky objects around that have fallen or been damaged in the wind, and they just simply have severe musculoskeletal injuries from strain and from heavy lifting that they're not used to under normal circumstances. It's also important to be on the outlook for structural instabilities in buildings that may look okay on the outside but in fact are unstable when people enter them. They're vulnerable to head trauma or more severe injury.

And finally, there are often reports or concerns about hazardous materials. In the context of flooding or hurricane, many containers and chemical receptacles can become dislodged or lay around the yard in the environment and you don't always know what's in them. So it's very important that people not handle those kinds of containers or equipment without knowing what it is and making sure they have the appropriate personal protective equipment to be safe.

There are many other tips again on the CDC web site that go into some of these areas in more detail, and I think for those who are in a position of concern, again, the most important thing is to contact local health officials or local utility officials, depending on the circumstances, to get locally specific advice in the environment.

I'm going to take one more question from the telephone lines before we end today. Is there another question?

OPERATOR: Thank you. Avila Clair, you may ask your question. Avila Clair, your line is now open. Please check your mute feature.

[No response.]

OPERATOR: Thank you. We'll take Peter Gorner. Your line is now open.

QUESTION: Doctor, any idea why the Illinois totals of West Nile this year are so incredibly profoundly low compared to last year?

DR. GERBERDING: I don't know for sure, but we have some ideas to account for changes from year to year in the distribution of West Nile virus. As you know, the disease epidemic is dependent on many factors, including weather and rainfall, but also the host, and in this case the bird population is the major place where the virus replicates, and the pool of infected birds is a major variable that affects the degree to which--mosquito bites the bird, and then the mosquito bites a human being and transmit infection.

Bird migrate, and in the areas that have had heavy burdens of West Nile in one year, there is a potential for some carryover immunity, so that the bird population is partially protected from West Nile virus either for the season or at least for the early part of the season. As new fledglings are born, of course, they don't inherit the immunity, so birds that appear later in the season may not have protective immunity from the year before, but at least that is one explanation for why a hard-hit area one year may not be as hard hit the next year. And we do see that pattern with other mosquito-borne illnesses that involve birds as vectors.

So it's too early to say for sure, and I would advise the people in Chicago to continue to take the steps to protect themselves because we're not out of the season yet, so to speak, and we don't want to end up where we were last year, which was late in the season Illinois and Ohio and some of the other midwestern states had a very dramatic rise in cases.

So until mosquito season is over, it's very important to fight those bites.

Thank you very much for your attention today.

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