Transcript for CDC Telebriefing: Zika Telebriefing Update

Press Briefing Transcript

Friday, September 23, 2016, at 1 P.M. EST

Please Note: This transcript is not edited and may contain errors.

OPERATOR: Welcome, and thank you for standing by.  Today’s conference is being recorded.  If you have any objections, you may disconnect.  All participants are in a listen-only mode until the question-and-answer session at the end of today’s session.  During that time, to ask a question, please press star one.  I would now like to turn the call over to your host, Michelle Bonds the Director of The Division of Public Affairs.  You may begin, ma’am.  Thank you.

MICHELLE BONDS:  Thank you, Michelle.  And thank you all for joining us today for the briefing on today’s MMWR release, local mosquito-borne transmission of Zika virus, Miami-Dade and Broward county Florida June through August 2016.  Joining us today is Dr. Tom Frieden and Dr. Celeste Phillip, surgeon general of the state of Florida.  I’ll now turn the call over to dr. tom Frieden.

TOM FRIEDEN: Thank you very much for joining us.  Today’s MMWR is an important milestone in the Zika response.  The actions by Florida doctors, epidemiologists, public health experts and mosquito control specialists interrupted the spread of Zika in the Wynwood community, preventing further spread of the virus and protecting the community, most importantly, pregnant women.  I’d like to step back and give some historical context that’s really important to understand how notable these findings are.  The Aedes Aegypti mosquito is really, really hard to control and once an outbreak with it has started, that’s extraordinarily difficult to control.  Traditional measures have had very limited success controlling outbreaks caused by this mosquito, and once the viruses spread by the mosquito have begun to travel through a community, they often continue to spread for a long time.  For more than a year in the case of Dengue in the Florida Keys, despite extensive control efforts.  To continuously eliminate standing water, particularly in places where it rains a lot, is nearly impossible.  In many parts of the world there is extensive use of truck-based spraying when Dengue outbreaks occur, but there has been little or no evidence that that is helpful.  What’s key to show are two different things.  First, can you control the mosquito, and second, can you slow or stop the spread of the disease.  This is very hard because as demonstrated by Dengue, it can spread even with very low levels of mosquito infestation.  I want to be clear about what today’s MMWR does and does not show.  We cannot know with certainty that the control measures ended transmission, and of course the virus could come back tomorrow.  But, having said that, the findings are clear.  Despite extensive ground-based efforts, there remained large numbers of mosquitos, and Zika continued to spread among people in the area.  As soon as aerial spraying was done, mosquito populations plummeted and monitoring found no more people infected in the weeks after the aerial application.  And I want to just draw your attention to figure three of the MMWR.  If you look at the dashed downward arrows where the Naled or aerial insecticide was applied, you see rapid and dramatic reductions in mosquito counts in the traps in that area.  I’ll go into that a little bit more in a moment.  There’s an enormous amount of information in this MMWR and I think it will answer many questions that people have had about what is going on and has been going on.  While I’m sure that all those online are reading it very carefully, I do want to highlight several of the key findings.

First, there were two unrelated, isolated cases of what appeared to be locally transmitted Zika.  That’s what we expect.  With Dengue, about nine out of ten instances of local transmission stopped with a single case.  In contrast, second, in Wynwood, the Florida department of health and the CDC devised a new method to look for new infections, and this method found a large number of infections in the inner six-block area but no locally acquired infections elsewhere within a one-mile buffer zone.  Third, mosquito counts remained high despite high quality and dedicated efforts and the use of three different insecticides along with parricides in ground spraying.  Fourth, mosquito counts fell rapidly as soon as Naled was applied by air.  They were more than 90% kill rates in traps and a rapid reduction in mosquito populations.  Naled was selected for use after testing demonstrated a potential resistance to other commonly used adult asides but it’s important to emphasize also that this is not the kind of spraying that some people think of when they think of aerial application spraying.  It’s ultra-low volume spraying.  It uses less than one ounce per acre.  it uses a very, very tiny micron-sized droplet that allows the droplet to stay in the air for an hour or two and to get under bushes, under leaves, in places where the Aedes Aegypti mosquito may rest or hide.  It also breaks down rapidly in the environment after that.  Fifth, outside of that two-mile area where Naled and EPI were applied, only Naled was used.  In that area mosquito populations bounced back rapidly and spraying with only Naled didn’t have the same effect reducing mosquito populations.  Using the one-two punch of Naled plus the BTI, a natural product that kills mosquito larvae, was a combination that rapidly controlled mosquitos and the mosquito counts have remained relatively low since then.

Also, the Florida health department did what is called syndromic surveillance.  This is a highly sensitive method of checking the emergency department chief complaints from hospitals in the area, working them back to the zip code of relevance, and they found no increase in any type of respiratory, skin or other complaint during the system.  We won’t know if what worked in Wynwood will necessarily work in all environments, but there are nevertheless, important implications.  All areas that have Aedes Aegypti mosquitos in the U.S. need to be ready.  They should have ongoing capacity for comprehensive mosquito control.  What Florida implements was a comprehensive program of source reduction with getting rid of standing water, ground-based application from trucks and backpack sprayers and aerial application of products that can safely and effectively control both larva and adult mosquitos.  New tools are needed and should be assessed.  At this point aerial application appears to be our strongest tool, so new tools, new developments, will not be assessed against that.

This report shows that aerial spraying with BTI which controls the young mosquitos and Naled, is an effective addition to comprehensive mosquito management and currently the most effective tool in the Zika prevention toolbox. We understand and respect concerns some have over the use of pesticides such as Naled.  In fact, at CDC we’ve been working hard to develop new means of controlling mosquitos, including with insecticides that have no toxicity in any circumstance.  But the plain fact is we do not have a vaccine against Zika, and the mosquito that spreads Zika is very difficult to control.  Our best chance at fighting this disease is to both encourage pregnant women to not go to areas where Zika is spreading and where we have new clusters to rapidly knock down infected mosquito populations as rapidly as possible.  It’s understandable that people have questions about Naled.  Naled has been studied by the eta and has been found to be safe and effective when applied according to label instructions.  Its use will reduce the immediate threat presented by mosquitos that carry Zika.  At CDC we have on multiple prior occasions studied with a super sensitive assay to see if there’s any human absorption of Naled after aerial spraying of ultra-low volumes, and we have not detected any exposure in people in those communities.  As we’ve said since the beginning of the Zika epidemic, we continue to learn something new every day.  Today we’re reporting that aggressive mosquito control can rapidly knock down Aedes Aegypti mosquito population.  Naled has been proven for decades but it’s never before been proven to stop the spread or interrupt the spread of human disease.  We continue to work closely with Florida health officials to find and prevent ongoing Zika virus transmission in Miami Beach.  Mosquito season continues through the fall so additional cases could well be identified.  In the Florida Keys transmission may have continued year-round.  We recommend that people living in the area strictly follow steps to prevent mosquito bites and that pregnant women avoid travel to the 4.5-mile area of Miami Beach where active transmission appears to be ongoing, and we advise all state and local health departments to continue monitoring for new evidence of Zika transmission.

The bottom line is that Florida’s rapid response to Zika in Wynwood appears to have interrupted spread of the virus there, and aerial spraying appears to be, a if not the key driver in this progress.  We understand that people are worried about the use of Naled.  When applied properly aerial spraying can be done safely and effectively.  In contrast, we’re certain that Zika causes not only microcephaly but also other birth defects, and I think we all can agree that pregnant women deserve protection against Zika in their homes and their communities.  I want to also thank Dr. Celeste Phillip, Surgeon General of the Florida Health Department for her leadership in this response.  Florida is on the front lines.  They have excellent mosquito control programs.  They’ve been doing an excellent job on the response and we’re happy to be working in complete partnership with them.  This is their report which they’re the first to author.  I’ll now turn it over to Dr.  Phillip for additional details and remarks.

DR. CELESTE PHILIP: Thank you, Dr. Frieden.  This report outlines the process that the department of health along with all of our partners undertook to identify the first mosquito-borne local transmission in the U.S.  during late June through early August we believe that 29 people in the Wynwood area — excuse me, 30 people in the Wynwood area were identified as having been infected with Zika virus  through local mosquito-borne transmission.  As a part of our initial work, we identified a few other singleton cases or, as Dr. Frieden mentioned, individuals that after our thorough investigation and questioning we found that there was no other cases associated with them.  This report walks through the processes that we took to interview and test.  We overall in the Wynwood area tested 521 people were 38 that were found to have evidence of infection, either meeting the case definition or having positive lab results but were asymptomatic.  The efforts to interrupt transmission were very comprehensive and we believe in the end that is what allowed us to achieve 45 days of no local transmission of Zika in the Wynwood area which occurred this past Monday.  Our work focused on interviewing testing employees and people who lived within 150 meters of two work places that came to our attention through our investigation because of multiple individuals there that have symptoms and eventually tested positive for Zika.  So we used that information to then decide the additional individuals in that area that should be tested. Part of our approach included working with a clinic that was in the area for us to get additional samples, and also working very closely with our local partners in the mosquito control district and our department of agriculture to track and test mosquitos.  We believe that the comprehensive efforts were effective in allowing for us to see this disruption or interruption of ongoing transmission in the area.  in addition to the aerial larva siding and adult siding, we greatly increased the number of boots on the ground to be able to reduce the number of sources as much as possible, to make sure that those in the area were aware of what their role is for eliminating standing water in their yards or workplaces, and again the importance of using repellant.  So we believe all of these efforts allowed for us to see the success that we’ve achieved thus far.

However, we know that we continue to see travel-related cases from other countries coming into our state, coming into Miami-Dade, and we continue to emphasize the importance of those travelers using repellant upon their return.  We also continue to remind individuals to be aware of the recommendations regarding sexual transmission.  Now, there is a longer period of time that condom use is recommended.  All of these efforts are with the emphasis on how we all have a role to play to protect the pregnant women in our state, in particular, this part of Miami-Dade.  We hope to see the same success in Miami Beach, and we are replicating many of these efforts there as well.  We are very grateful to the mosquito control district, our county health department, Miami-Dade, our state partners, as well as CDC for their support, and I think it wouldn’t have been possible without all of us working together for us to be at this point where we are now.  I will turn it back over to Dr. Frieden. Thank you.

TOM FRIEDEN: Thank you.  Michelle, would you like to open it up for questions.

MICHELLE BONDS: Thank you.  Michelle, we’re ready for questions.  I want to add that we have Richard Keigwin, Deputy Director of the office of Pesticide Program with the EPA on the line to assist with any questions.

OPERATOR: to ask a question, please press star one and record your name clearly for question introduction.  Again, to ask a question, star one and clearly record your name for question introduction.  Our first question will come from Peter King with CBS News.  Your line is now open.

PETER KING: great, thank you very much.  Good afternoon to everyone on the call.  You’ve just said that aerial spraying was effective in Wynwood, ground spraying not effective there.  I want to go across the water to Miami Beach where the geography is different.  There are many more tall buildings there and that seemingly limits the possible effectiveness of aerial spraying.  So my question is, is there hope that aerial spraying really could be realistically effective there, and if not, what is your back-up plan?

TOM FRIEDEN: thanks, and I’ll start and Dr. Phillip can continue.  As we said from the outset the environmental conditions in Miami Beach make it more challenging to apply aerial spraying, however, aerial spraying has been applied and the initial data suggests in the areas where it is being sprayed a similarly rapid knockdown in mosquito populations.  We can’t measure mosquitos everywhere, so we don’t know that that has happened to the same extent, but it has been encouraging result so far.  Dr. Phillip, would you like to add?

DR. CELESTE PHILIP:  I certainly understand that question because i think early on there was a fence that aerial spraying would be difficult with Aedes Aegypti mosquitos in particular.  As we’ve learned along the way the multi-disciplinary or multi-pronged approach to how we can take advantage of all the tools in our toolbox if you will, we saw that success in Wynwood and had discussions regarding the potential for using the same approach in Miami Beach.  We are closely monitoring our numbers and again are hopeful that we will see the same success.  But this is a new process for a part of geography that has a lot of tall buildings, so I think we are cautiously optimistic.

MICHELLE BONDS: Next question, please?

OPERATOR our next question will come from Dan Vergano from Buzzfeed news.  Your line is now open.

DAN VERGANO: hi, thanks.  I’m Dan Vergano with Buzzfeed news.  I’m wondering if the success you’re talking about here means this should be used more widely elsewhere.  is this approach being used in population centers in places like Puerto Rico or elsewhere?  Should it be used more widely, or is it already being used?

TOM FRIEDEN: This has been the first application of aerial Naled plus BTI for control of Zika that we are aware of anywhere.  So there had been prior use of Naled plus BTI in Florida, Louisiana, and elsewhere for control of Aedes Aegypti, but not in the context of an outbreak of Dengue or Chikungunya or Zika, three viruses spread by this mosquito. So what’s new here is the first interruption of the spread of the disease carried by this particular mosquito.  The only place in the continental United States that we’re currently aware of that has ongoing or appears to have ongoing spread of Zika is that 4.5-mile area within the Miami Beach neighborhood.  Over the past months, discussions about whether or not to use aerial spraying in Puerto Rico were taken and the governor there decided not to proceed with that.

MICHELLE BONDS: Next question?

OPERATOR: Our next question will come from Kerry Sheridan from AFP.  Your line is now open.

KERRY SHERIDAN: Thanks for taking my call. Just to follow up on that, do you know, Dr. Frieden, why Puerto Rico decided not to pursue that, and as a second question I was wondering if you could tell us, how certain are you that Naled was really effective?  I saw in the report itself that one of the caveats was it can’t be said for certain that this was, so what do we make of that?  Thanks.

TOM FRIEDEN: thank you.  I think there are understandable concerns about the impact on the environment and the impact on humans. I think in some context there’s also been a lack of recognition of the severity of microcephaly and the sad certainty that we will be seeing many babies born with microcephaly in Puerto Rico as well as in other places.  The second part of your question was?

KERRY SHERIDAN: The second part of the question was about the MMWR report itself points out that one of the drawbacks so the study was it couldn’t be certain that the pesticide was really what caused the decline.  I’m just wondering how to rectify that with what you’re saying on the call today.

TOM FRIEDEN: Thank you.  Yes, this was not a controlled trial, so we didn’t go into two communities that had Zika spreading and use aerial spraying in one and not use it in the other and see if there was a difference.  This was a real world application with very rigorous analysis of what the real world data showed.  I would point again to figure three in the MMWR report which is really quite striking.  The mosquito counts were high despite the continued and expert application of ground-based approaches.  Then when aerial Naled was applied, there was a rapid drop-off in the mosquito count.  As another crop of mosquitos hatched, it began to rebound.  With additional applications of Naled it again fell.  Now with the application of BTI to kill the larva mosquitos so more crops of mosquitos don’t emerge, it has remained at a very low level in the surveillance there.  So I think we’re giving all the information openly and transparently.  It’s certainly very highly suggestive that when the application was done by air, there was a rapid knockdown that had not occurred before.  Also quite striking that in the areas that only used Naled and didn’t also use the larvacide BTI, mosquito populations rebounded.  So it does appear that that one-two punch is important, and this is also exactly the time when spread from person to person stopped.  There were very important other measures that were undertaken.  Comprehensive mosquito control is important.  People getting rid of standing water so you can reduce the number of mosquitos.  Application by truck and sprayer by staff to focus on problem areas, wells or other places where there might be large numbers of mosquitos breeding.  But the information here clearly shows that in terms of the time course, aerial application of Naled plus BTI is associated with the rapid interruption of transmission.

MICHELLE BONDS Next question, please?

OPERATOR: Our next question comes from Debra Goldschmidt with CNN Health.  Your line is now open.

DEBRA GOLDSCHMIDT: Yes, can you — talked about — Dr. Phillips, about the application being new territory with these tall buildings in Miami Beach.  there has been some discussion about how that is being done via an airplane versus having it done with a helicopter which a lot of experts have said would be more effective because it can get lower and closer and get the spray into more places.  Can you speak to that and talk about also secondarily what effectiveness you’re seeing with the Naled aerial spraying by plane that you’ve done so far.

DR. CELESTE PHILIP: I can share some initial comments and then i might turn it over to Dr. McAllister if she’s still on the line. We did have discussion regarding fixed wing versus helicopter spraying, and given the wind drift and the considerations regarding how far the droplets had to travel, and the plane could be offshore versus with the helicopter needing to be closer to the buildings and potential risk there in terms of safety for the pilots, the decision was made to use the airplanes.  The thought would be that it would be just as effective.  And I can tell you that our count numbers — our track numbers are lowering similar to what we’ve seen in Wynwood.  So that’s why we are cautiously optimistic that we are seeing similar success there.  But I can turn it over to Dr. McAllister if she wants to add some comments.

DR. MCALLISTER Yes.  This is Dr. McAllister.  I’m actually in Miami right now and we have a thunderstorm going on so I did not catch what the question was.

TOM FRIEDEN:  I think we can probably go to the next question.  The question was simply a fixed wing versus helicopter application and the entity that does the spraying felt that the more secure way to do it would be using fixed wing.  As Dr. Phillip said we’ve been seeing encouraging knockdown of mosquito counts.  I think we can take the next question.

OPERATOR: Next question comes from Robert King with the “Washington Examiner.”  Your line is now open.

ROBERT KING: Hi.  I have a quick question about the safety surrounding the use of aerial spraying. As I believe it, this product, Naled, has been banned in the European Union. What can you say to people that are still kind of concerned about the safety of aerial spraying?

TOM FRIEDEN I’ll begin and then turn it over to our colleague from the EPA to continue.  This is Tom Frieden.  In Europe, Naled is not registered.  There are many products that are used in the U.S that are not registered in Europe.  They have a somewhat different approach used to the registration of products.  In the U.S. we look at the use as it is used, not necessarily the chemical itself.  The point here is that when used according to label instructions per EPA registration, it can be used safely.  But I’d like to turn it over to our EPA colleague for more comments.

RICK KEIGWIN: Thank you, Dr. Frieden.  This is Rick Keigwin at EPA.  Yes, when used according to the EPA accepted label, EPA has determined that the use of Naled through aerial application is safe. As we understand it, there’s a different infrastructure for delivery of mosquito control in Europe and it’s typically not via aerial application.  The company who manufactures Naled for business reasons chose not to pursue or continue registration in Europe.

MICHELLE BONDS: next question, please?

OPERATOR: our next question comes from Steve Reinberg from health day.  Your line is now open.

STEVE REINBERG: I was wondering, do you know how many locally transmitted cases there have been in Miami Beach?

TOM FRIEDEN: Dr. Phillip?

DR. CELESTE PHILIP: So far associated with the Miami Beach investigation we have 44, I believe. Excuse me, I’m sorry.

TOM FRIEDEN:  We have time for two more questions.

OPERATOR: Our next question will come from Sandee Lamotte with CNN.  Your line is now open.

SANDEE LAMOTTE Hello there.  Dr. Phillip, you said earlier that you did not — you were happy to see an interruption of the situation in Wynwood.  Does that mean that it might occur again, that further exposure might occur considering that that interruption is only from last Monday?

DR. CELESTE PHILIP:  As I stated earlier, we are seeing a number of imported Zika cases from residents and visitors who traveled to other countries and come back into our state and then test positive for Zika.  So our approach is that we will continue the same efforts and encourage those travelers to take proactive steps to protect themselves from getting bites here.  If they are infected because that’s how the transmission occurs locally.  And so that’s really the comment, that we believe we have interrupted the transmission but because we see more introductions of Zika from travelers in particular, we have to stay vigilant.

TOM FRIEDEN: let me clarify that transmission appears to have stopped in early August right as the spraying started, the aerial spraying started.  Last Monday was the 45-day, three incubation period time after that.  We’ll take our last question.

OPERATOR: Our last question will come from Ransdell Pierson from Reuters.  Your line is now open.

RANSDELL PIERSON: Dr. Frieden, I wanted to ask you, the one-two punch we’re talking about here, does that give you greater confidence that we’ll be able to contain this virus in the country as a whole, particularly the gulf coast and other nearby areas?

TOM FRIEDEN:  This is certainly a new tool for our tool kit and the strongest one we have for where we have local transmission. It’s part of a comprehensive mosquito control program that includes encouraging people to get rid of standing water on their property, pregnant women in particular to protect themselves against mosquito bites, the controlled programs to track mosquito populations and target problem areas for ground-based application.  But this really does herald in a new era of a standard of control for local transmission. That it appears that the aerial application of this one-two punch has the ability to rapidly interrupt transmission.  It doesn’t mean that area is immune from future spread because mosquitos or infected individuals can come back and infect more mosquitos, but the findings are quite striking.  Those who have worked in the field of Arbo-virology and diseases spread by Aedes Aegypti and have looked carefully at this data are struck that we haven’t seen similar control in other diseases spread by this particular mosquito species.  though we’re not certain because it was not a controlled trial, the data are certainly suggestive that in the context of a comprehensive mosquito control program, the addition of aerial application of the one-two punch of Naled plus BTI resulted certainly in the rapid control of the mosquito population and apparently in the interruption of transmission from person to mosquito to person.  Aerial spraying appears to have been a, if not the, key driver in this progress.  We do understand that people are worried about the use of Naled.  We wish insecticides never had to be used.  We wish Zika were not causing birth defects also.  In the balance between protecting pregnant women and the next generation against devastating birth defects, we’re encouraged that there is now a new tool that appears to have had such dramatic results in Wynwood.  I want to thank you all for joining us and we’ll be available for follow-up information.  There is a lot of information in the MMWR.  I want to really give credit to Florida, not only for its success in this response but also for writing up this very important report so that it’s out there, we can all look at it and understand what it does and doesn’t show.  Thank you very much.

MICHELLE BONDS: Thank you, Dr. Frieden, Dr. Philip and Dr. Keigwin for joining us today, as well as all the reporters. For follow-up questions, please call the press office at 404-639-3286 or send an e-mail to  Thank you for joining us.  This concludes our call.

Page last reviewed: September 23, 2016