CDC Telebriefing Transcript

MMWR: West Nile Update and E. coli 0157:H7 Contaminated Beef
with
Dr. Daniel O'Leary and Dr. Paul Mead

July 25, 2002

CDC MODERATOR: Hi, and welcome to today's telebriefing. Today's briefing will actually feature two speakers. We will begin with the Article, "Weekly Update: West Nile Virus Activity--United States, July 17-23, 2002," followed by the "Multi-State Outbreak of E. coli 0157:H7 Infections Associated with Eating Ground Beef, United States June-July 2002."

Our first speaker is Dr. Dan O'Leary, and he will discuss the West Nile Virus activity.

Dan?

DR. O'LEARY: Thank you, KD.

I want to just give a brief summary, that during 2002, West Nile Virus activity was reported to the Centers for Disease Control and Prevention from 25 states, New York City, and the District of Columbia.

There have been a total of 12 human cases of brain infection with West Nile. All of those cases were reported from Louisiana and Mississippi: eleven from Louisiana and one from Mississippi. Among these cases, eight were men. The range of ages was 34 to 88 years, and their dates of onset of illness ranged from June 10th to July 11th. None of these 12 cases are fatalities.

Additionally, there have been three states--North Dakota, Oklahoma, and Texas--that have reported their first-ever West Nile Virus activity, but so far only in birds, horses, and mosquitoes, with no human cases. The spread to these three latter states--North Dakota, Oklahoma, and Texas--demonstrate that West Nile Virus is continuing to move Westward in the United States.

Next, dead birds, particularly blue jays and crows, remain the most important indicators of West Nile Virus activity in a given region, and their collection and testing by state and local health departments should be a mainstay in these jurisdictions' surveillance programs. The capture and testing of mosquitoes is, additionally, very important as a mainstay of state-level surveillance, and additionally, surveillance for West Nile Virus in horses and other equines has proven a valuable surveillance tool to indicate the early earning of West Nile activity in select areas.

At a minimum, we're asking states to conduct human surveillance to include West Nile Virus testing for patients with encephalitis or of a cause to which other diagnoses cannot be ascribed.

The prevention message here is that human and animal illness prevention, it depends on sustained and long-term control of the mosquitoes that spread West Nile Virus, especially in populated areas. Detection should happen as early as possible, and it should be followed by intensified mosquito control in areas where the virus is found, especially in populated areas. People should also take personal responsibility for protecting themselves against mosquito bites, including the use of protective clothing and the use of repellents.

The final line is that West Nile Virus is endemic or it is now established in the United States and that personal protection against mosquitoes, effective mosquito control at the local level and early detection are all mainstays of prevention.

That is all I have, Katie, for now. I will turn it back to you.

CDC MODERATOR: Okay. John, we can now take some questions on West Nile.

AT&T OPERATOR: Certainly. Once again, ladies and gentlemen, if you do have a question at this time, please press the one.

Ms. Hoskins, no questions in queue. Oh, excuse me. We do have a question from the line of Richard Knox with National Public Radio.

Please go ahead.

QUESTION: Hi. Thanks for being available.

Do you have any hypothesis as to why there have not been more human cases as this has spread so widely?

DR. O'LEARY: Richard, usually people are--humans and horses--are what we call dead-end hosts for West Nile Virus. We know that the cycle of West Nile Virus is maintained in nature between birds and the mosquitoes that feed on the birds, and it takes a unique combination of circumstances for humans to be infected. Humans have to enter an area where this transmission cycle is taking place and then have to be bitten by an infected mosquito.

Now there are mosquitoes that will also occasionally feed on humans, and that can be then--that feed on humans and birds--and if those mosquitoes are present in an area where the virus is circulating, and a mosquito that will also bite a human becomes infected with the virus and can also go over and bite a human, now it takes that combination of circumstances for humans to be infected, and that combination of circumstances happens sporadically and somewhat unpredictably. This is why we don't see more humans I think being infected because most of the mosquitoes that are feeding on these birds like to have birds to feed on and do not preferentially attack humans.

Now we do urge the states to do--we think it is very important to do mosquito surveillance for those species that will feed both on birds and on humans and control those species whenever they are found infected with the virus.

QUESTION: Would you have expected more human cases than you have seen?

DR. O'LEARY: Not necessarily. Again, it just depends. These things are difficult to predict. It is hard to know where the virus is going to travel and into which ecological system the virus will end up, and so we don't have a--it is hard to formulate a clear idea of exactly where the virus is going to circulate intensively and then spill over and infect humans.

We are working with the states to intensify and increase mosquito surveillance to determine the species at the local level that are being infected and those which can potentially infect humans.

QUESTION: Thank you.

CDC MODERATOR: Do we have another question for Dr. O'Leary?

AT&T OPERATOR: Yes, we have a question from Martha Kerr with Reuters Health. Please go ahead.

QUESTION: Hi, Dr. O'Leary.

I am wondering if you expect the number of cases to continue to increase before they get better with surveillance and control of mosquitoes, et cetera.

DR. O'LEARY: When we look back at the epidemic in 1999 and in New York City, it started with a lower number of cases and then, as time went on, the number of cases did increase. It is hard to say at what point in this year's transmission season human cases will start to decline, but we are early in the transmission season. We are in the middle of summer, and we have an extended warm season in the South, so the mosquitoes in the South are actively feeding now and will continue to actively feed as long as the weather stays warm.

And so we anticipate that there is a possibility for an increase in the number of cases, since we are so early in the transmission system.

QUESTION: How concerned should people be? How easily treatable?

DR. O'LEARY: There is no specific treatment for West Nile Virus infection because it is a virus infection, and unlike bacterial infections, we don't have the luxury of antibiotics for treatment. The treatment is supportive, and so the key message that we want to instill in our states that we support and to the public is the message of prevention and taking personal responsibility, whenever possible, to avoid mosquito bites in areas where the virus has been detected.

Again, the use of protective clothing and the use of insect repellents are our mainstays of personal protection, and populations that are particularly susceptible to developing more severe disease, such as individuals over 60 years old may want to take the additional step of avoiding mosquito-biting areas or areas of mosquito activity during peak biting hours like dawn and dusk.

QUESTION: Thank you.

DR. O'LEARY: Sure.

CDC MODERATOR: John, do we have another question for Dr. O'Leary?

AT&T OPERATOR: Yes, from Jeanie Davis with WebMD. Please go ahead.

QUESTION: I wondered if things have gotten better on the East Coast, as far as number of dead birds and that kind of thing.

DR. O'LEARY: Well, we have detected West Nile Virus activity in most of the Eastern states again this year, so there is dead bird activity in all of the states where West Nile was detected last year. So the virus continues to infect and cause mortality in wild bird populations, particularly in crows and blue jays.

So there is an indication that the virus is present again this year in all of the states where it was present last year.

QUESTION: Just as present as it was before, huh?

DR. O'LEARY: Well--

QUESTION: The eradication efforts haven't really helped that much?

DR. O'LEARY: Well, when you're talking to eradication efforts, what you are really talking about is local mosquito control.

QUESTION: Right.

DR. O'LEARY: And there are many areas that have instituted local mosquito control. However, there is documented virus activity in many areas that, unfortunately, because of budgetary constraints, don't have mosquito control. So the virus can circulate in many areas away from population centers, away from the areas of mosquito control and can be reintroduced.

QUESTION: Okay. Thank you.

DR. O'LEARY: You're welcome.

CDC MODERATOR: We will now turn this half of the telebriefing over to Dr. Paul Mead, who will talk about the current E. coli investigation.

DR. MEAD: Good afternoon. In today's article, there is a report on an ongoing investigation of E. coli 0157 infections in seven states. To date, a total of 28 illnesses in Colorado and six other states have been linked to eating contaminated ground beef products recalled by ConAgra Beef Company on June 30th. There have been seven patients hospitalized. Five have developed hemolytic uremic syndrome, however, there have been no deaths among confirmed cases to date.

In addition to Colorado, states with confirmed cases include California, Iowa, Michigan, South Dakota, Washington, and Wyoming.

On June 30th, independent of the outbreak investigation, ConAgra Beef Company issued a nationwide recall of 354,000 pounds of ground beef products that were produced on May 31st. This recall was based on the detection of E. coli 0157 during routine microbiologic testing conducted by the United States Department of Agriculture. The results of the epidemiologic and laboratory study demonstrate that this beef was the source of illness in these patients.

A few other things. Last week, the recall by ConAgra was expanded to a nationwide recall of around 18.6 million pounds of fresh and frozen ground beef products and trimmings. I think the take-home messages from this are a few. One is that consumers should be reminded that they can reduce their risk of illness by buying meat that has been precooked or treated with electron beams. They can also protect themselves by using safe food practices. Specifically, frozen ground beef should be thawed in a refrigerator, rather than room temperature.

Ground beef should be cooked thoroughly to an internal temperature of at least 160 degrees Fahrenheit. Using a meat thermometer will help ensure proper cooking of ground beef, and to reduce the risk of cross-contamination, consumers are reminded to use soap and hot water to wash hands, utensils and other surfaces that might come in contact with raw or undercooked ground beef.

Finally, this outbreak demonstrates the importance of routine molecular subtyping in epidemiologic investigations. PulseNet, which is the national network for molecular subtyping of food-borne pathogens, played a critical role in detecting this outbreak and linking cases of E. coli 0157 infection with those in other states.

In addition, PulseNet was used to demonstrate that the same exact strain of bacterium was present not only in patients, but also in leftover meat recovered from patients' homes and from the recalled ground beef product by ConAgra.

I will stop there.

CDC MODERATOR: John, we are ready for our first question for Dr. Mead.

AT&T OPERATOR: Certainly. I will just throw a quick reminder, ladies and gentlemen, if you do have a question, please press the one.

We have a question from Judith Graham with the Chicago Tribune. Please go ahead.

QUESTION: Dr. Mead, have any illnesses been linked with the 28 lots of meat that were recalled last Friday? Not the June 30th production date, but the subsequent recall of 18.6 million pounds of fresh and frozen ground beef?

DR. MEAD: Currently, we do not have any cases that have been definitively linked to lots of meat that were covered under the expanded recall, but not under the initial recall. However, we cannot rule out the possibility that there may have been cases due to earlier lots of meat.

QUESTION: Are you looking at that actively?

DR. MEAD: Yes, we are. This is an ongoing investigation, and we are continuing to use PulseNet to identify cases that may be related. Certainly, as is typically the case at this time of year, there are other outbreaks of E. coli 0157 around the country. There is nothing particularly surprising about that.

Those outbreaks are being investigated, and obviously, if those investigations lead to ground beef, and ultimately to the source, then we will have evidence that might support that, but, currently, we do not have evidence of cases linked to other lots outside of the lot that was recalled on June 30th.

CDC MODERATOR: Do we have another question for Dr. Mead?

AT&T OPERATOR: Yes, from Richard Knox with National Public Radio. Please go ahead.

QUESTION: Actually, a couple. One is to follow up on what Ms. Graham just asked.

What would be the time window in which you might expect, if there are cases that are going to be linked to the more recent recall, that they might emerge? And then after that, I have a second question.

DR. MEAD: It is a little bit difficult to predict. Most ground beef has a shelf life of around two weeks, fresh ground beef, and consequently most cases will occur shortly after it is produced. However, ground beef can obviously be frozen for a long time, and it is possible that cases could occur well out, on the order of months out. One purpose of recalls is obviously to alert people who might have frozen ground beef of that possibility.

The expanded recall, I believe, comes up to a fairly recent time period. So, in general, I would expect that over the next few weeks, two to three weeks, we should have a better idea of whether or not there might be cases related to other lots.

QUESTION: Secondly, on the question of molecular subtyping, I notice in the MMWR article, you mentioned that this outbreak demonstrates the continuing importance of retaining surveillance, combined with molecular subtyping. I wonder if you could talk a little bit more about how, in this case, as you mentioned before, the subtyping, the finding of this unique strain in these key humans, in the ground beef left over, and in the ConAgra samples, how that affected the way this unfolded and in the ultimate recall history, compared to the old days before you could do that.

DR. MEAD: Right. It's a great question, and unfortunately--or not unfortunately--maybe fortunately, this a bit of an unusual event in the sense that there was recall of ground beef, and it was really independent of the epidemiologic investigation and of illness. It was taken, the initial recall, purely on the basis of testing conducted by USDA of meat products.

So, in that sense, that initial recall happened earlier than really the results of molecular subtyping were available. The role of molecular subtyping here was, first, to allow health officials in Colorado to identify which cases were part of a cluster and which cases are not.

That is often very important because you are trying to establish what is common to the cases, and if you have people who are actually infected with slightly different strains, they likely got their infection from another source. Therefore, you won't find a common link between those.

So, in Colorado, it helped to identify the group of patients who hand something in common, and that allowed investigators to find that they had all purchased ground beef from a particular grocery store and through that begin to make a link to the ConAgra meat.

Second, molecular subtyping through PulseNet allowed us to look at isolates appearing or bacteria recovered from patients in other states to determine which ones might be related by comparing the pattern from patients in Colorado with patients in other states. We were, again, able to identify some cases that appeared to be caused by the same strain and rule out other cases which seem to be caused by other strains.

Then, finally, having the PFG pattern from the recalled meat, it was possible to demonstrate and confirm the epidemiologic findings of the Colorado Department of Health; that is, that not only had patients eaten meat that came from the store that got some of the recalled meat, but in fact they were infected with the exact same strain that had been found in the meat that had been recalled. So it provided confirmation of that, and in short order.

QUESTION: One other thing. Did the availability of this kind of molecular evidence have something to do with the greatly expanded recall that occurred? In other words, would that not likely have happened unless you'd had that kind of evidence in hand?

DR. MEAD: Well, the expanded recall, if I understand it, is based primarily upon investigations done by FSIS, the Food Safety and Inspection Service at USDA, and their investigation of the manufacturing facility. I would really need to defer to them to discuss the relative motivations for expanding and to what extent they expanded it. I believe that is based on their inspection and whatever testing was done there.

CDC MODERATOR: Do we have another question for Dr. Mead?

AT&T OPERATOR: Yes, we do have a follow-up from Judith Graham. Please go ahead.

QUESTION: Hi. I wanted to know whether ConAgra had allowed you to receive samples of the other meat that had been infected with E. coli, the 19 million pounds, and whether you have done molecular subtyping on those E. coli strains, and whether, in fact, they match or are dissimilar to the May 31 strain that has been tied to this outbreak.

DR. MEAD: We do not have those isolates, and to my knowledge, they have not been subtyped by PFG or posted to the PulseNet system.

QUESTION: Are you expecting that you will receive those?

DR. MEAD: We are actively pursuing that issue, basically through discussions with the Food Safety and Inspection Service.

QUESTION: Is there a problem? One would think that in order to be able to tie any other E. coli outbreaks around the country, you would need those subtypes. So I guess--I heard you say you were actively pursuing that issue. Are you confident you will be able to get the sample?

DR. MEAD: I don't know that I can really answer that. Typically, and part of this again relates to FSIS's investigation, I only know from media reports or I know from media reports that E. coli was recovered from other production days at that plant. It is my understanding that that is based primarily on testing that the company did.

QUESTION: Right.

DR. MEAD: To my knowledge, there is no legal requirement that the company share those strains with us and, frankly, I don't know that the company would still have those strains.

CDC MODERATOR: Do we have another question for Dr. Mead?

AT&T OPERATOR: No further questions.

CDC MODERATOR: This concludes our telebriefing today. I want to thank Drs. O'Leary and Mead for participating.

DR. O'LEARY: You are welcome.

AT&T OPERATOR: Ladies and gentlemen, that does conclude your conference for today. We do thank you for your participation, and you may now disconnect.

[Whereupon, the telebriefing was concluded.]

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