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Dengue: The Key West Tour

Posted on by Ali S. Khan
Aerial view of Key West (circled in red) off the coast of Florida
Aerial view of Key West (circled in red) off the coast of Florida

I often get asked about mosquito-borne dengue fever in the context of climate change. One of the first things I tell people is that it’s actually quite common outside the United States. Between 50 and 100 million cases occur each year, including about 500,000 of the really severe hemorrhagic fever type, and the numbers continue to increase. This increase is due to the usual suspects: more people moving into cities with poor sewage and scattered water containers that breed mosquitoes, increased international travel spreading the mosquito and viruses, and poor public health systems to control the mosquitoes.

Busy, urban areas with tropical climates and standing water help spread dengue
Busy, urban areas with tropical climates and standing water help spread dengue

The second thing I tell people is that dengue caused outbreaks here in the United States in the 1800s and beginning of the 1900s – and we still have the right mosquitoes to spread disease in the southeastern United States.  And yet, despite at least 100 travelers diagnosed with dengue each year in the United States and frequent epidemics right across the US border with Mexico, we have seen only a handful of local cases in Texas. [Note: We are also seeing an epidemic in Puerto Rico, but that’s for another post.] This all changed last summer when a local outbreak of dengue emerged in the Key West area after a 70-year absence; the outbreak affected an estimated 5% of the population (see report). Most recently, a 41-year-old man in Key West was confirmed to have dengue. He went to a military medical facility on April 6th, was referred to Lower Keys Medical Center, and from there was referred to a hospital in Miami, FL. The doctors there diagnosed him with dengue on the basis of his symptoms, and lab results later confirmed their diagnosis. The man reported not having traveled outside the country in the last year, suggesting that he contracted dengue virus locally.

After being hospitalized for five days, the patient fully recovered. Public health authorities in Key West and elsewhere in Florida are advising that people avoid mosquito bites and eliminate mosquito breeding sites in their homes. Florida’s public health authorities are working with the Florida Keys Mosquito Control District to try and decrease the local mosquito population.

So the big question is whether this case represents a persistence of last year’s outbreak or a new introduction of dengue from an outside traveler. What do our readers think?

Dengue: the Facts

Dengue is caused by a virus (to make matters worse, there are actually four separate but related dengue viruses, all of which cause disease) and is often called “breakbone fever” because its main identifying symptoms are high fever and aching bones or joints. Other symptoms include intense headache, pain behind the eyes, minor bleeding (for example, nose or gum bleeding), and sometimes a rash. The symptoms can last for about a week. There is no vaccine or antiviral medicine for this disease, so those who have dengue-like symptoms should see a physician. In about 1 to 5% of all cases, a person’s condition can actually worsen when the fever comes down. These patients need to be hospitalized for frequent monitoring of their blood pressure, administration of intravenous fluids, and other supportive therapy. 

Female Aedes aegypti mosquito taking a bloodmeal
Female Aedes aegypti mosquito taking a bloodmeal

The viruses are spread through the bite of infected mosquito species belonging to the genus Aedes. These mosquitoes are black with white stripes on their bodies and legs, so they’re pretty easy to spot. Almost everything about these mosquitoes makes them ideally suited for life with humans. For example, they like to feed at dusk or dawn but will feed during the day in shady areas or at night if the lights are on. They also tend to live inside or around houses and lay eggs wherever there is standing water (which could be in flower vases, pet water bowls, or on the surface of outdoor trash that has collected rainwater). These pests tend to live in tropical and subtropical regions, but these regions include areas of the southeastern United States and surrounding territories like Key West and Puerto Rico (see WHO map).

Methods to prevent contact with mosquitoes include:

  • Remove any sort of standing water from in and around your home
  • Wear long-sleeved shirt and long pants and use mosquito repellent
  • Make sure screens are in place and don’t have any holes by which mosquitoes can enter
  • Use air conditioning whenever you can (mosquitoes don’t like the cold, dry air)

For more information about dengue, its symptoms, and its spread, see CDC’s dengue webpage (http://www.cdc.gov/Dengue/), and the most recent update (http://www.cdc.gov/dengue/dengue_upd/).

Posted on by Ali S. KhanTags , ,

11 comments on “Dengue: The Key West Tour”

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

    How long does it take for mosquitoes to breed in the water? I always have water near my home.

    1. You circle most of the Keys. Key West is actually only a 2X4 mile area on the extreme southern tip. Then too, the transmission so far is only confined to the Old Town section which has a resident population of only 6,000.

    2. There are several “big” questions more important then the one posed:

    a. Why is transmission confined to Old Town when residents in other sections of Key West also were shown to have recent dengue infections?

    b. Why has the public health department not been able to break the transmission cycle in a very focal and geographically small area?

    c. What has the U. S. and the state done to stop the transmission cycle in Old Town?

    d. What will be the U. S. and state response to reduce the dengue of dengue if it spreads north into other more South Florida populous urban centers?

    e. Why has there been so little attention with aggressive community, state and federal action to this outbreak where 10% of the residents (over 2 years) have been infected, and the incidence of reported cases currently at 5/1000 Old Town residents rivals epidemics elsewhere in the world?

    f. What will happen in Old Town if a different Dengue serotype enters resulting in 10% of the residents at risk for Dengue hemorrhagic fever and dengue shock syndrome?

    3. As for your big question. Consider these facts. Key West has not had dengue for 70 years. DENV 1 arrived in 2009. DENV 1 appeared again in 2010. Which is more likely? Two unrelated subsequent arrivals of the same serotype in 2 years, or survival of the same serotype at a low level in the resident population and mosquitoes.

    The big question remains “can the U. S. stop dengue transmission in this very small confined focal outbreak?” Moment of truth.

    I live in old town key west and just got over this fever. The thing is, when I had it, I had no idea what it was. I even went to the pharmacy and described my symptoms to see if it was an interaction with a new prescription, and they had no idea (thought it was a flu.) Even though the severe pain behind my eyes should have been a dead giveaway of dengue.

    I agree with the poster above. The community here is denouncing CDC statistics because it hurts tourism; instead of doing further testing for more accurate statistics (which it seems like they wouldn’t want.)

    I fear to protect business interests Key West is setting itself up for major problems when the next strain of dengue comes through here and actually starts killing people.

    Thank you for your thoughtful reply, Walter. As you note, the focus of the dengue outbreak in Florida appears to be in Old Town Key West, with 45 dengue cases reported as of October 2 in 2010. However, there has not been the same degree of clinical awareness to look for cases in other parts of Monroe County. We agree that what happened in 2009 and what is happening in 2010 appear to be related. However, only time will tell.

    You’ve asked about the steps taken to control dengue transmission in Key West. It’s important to point out that control measures are executed by state and local authorities; CDC and other federal authorities can only intervene when requested by the state or when a public health emergency is declared. Specifics about the methods of control used are therefore best directed to the local authorities. Your questions point to an essential challenge in public health. Obviously we cannot determine what level of dengue activity Key West might have seen or how far activity might have expanded without the aggressive control measures that have been implemented by state and local authorities. Nonetheless, the continuation of dengue transmission in 2010 does imply that, even in Florida—with some of the best mosquito control programs in the US—we do not presently possess the combination of resources and technology needed to control Aedes aegypti mosquitoes to the degree necessary to eliminate dengue transmission. This also makes clear the challenges faced in developing countries with endemic dengue. Clearly, novel approaches will be needed to control this vector and reduce the burden of disease.

    CDC and other health and mosquito control authorities never stopped being concerned about dengue or other arboviruses. For a time, with the sweep of West Nile virus across the US in the mid- 90s, there were renewed attention and increased resources for mosquito-borne diseases. Since then resources have contracted in the face of lower West Nile activity and the poor economy. This dengue outbreak has again brought serious attention to dengue and Aedes aegypti control in the US. Ideally, we are able to capitalize on this renewed interest and move the field of dengue control ahead, both in the interest of the US and to address the dengue epidemics worldwide.

    First of all, we’re sorry to hear that you had dengue fever.

    State and local authorities, in collaboration with CDC, have been working with local physicians to increase knowledge about dengue, including the warning signs of more severe cases that would require prompt and aggressive treatment. Your post suggests it would also be wise to reach out to pharmacy employees as well so they can guide people with dengue-like symptoms to seek medical attention.

    The effect on tourism and the local economy is often a concern when disease activity occurs. This points to the need to communicate openly about the outbreak and the many ways that citizens and visitors can protect themselves. You mention the need for more accurate statistics: While further study can always help to better understand the patterns of disease outbreak and options for control, the statistics from the study already conducted are sufficient to know that an estimated 5% of the Key West population was exposed to dengue in 2009 (not necessarily sickened, as dengue infection may occur without causing symptoms or symptoms may be “written off” as flu, as you have noted is possible). With the continuation of transmission in 2010, additional people have been infected. Fortunately there have been many steps taken by the health department and mosquito control authorities to reduce dengue transmission, but all agree that aggressive control will be needed to continue to reduce the risk of DHF cases in the future.

    I appreciate and understand the comments pointing out the difficulties in controlling Aedes aegypti to reduce dengue transmission. However, I must continue to express my dismay that transmission continues in Key West, in the Old Town section, in this focal epidemic in ca. 2X4 mile area, and the public health community of the U. S. apparently seems unwilling or unable to provide the resources to stop it. By resources I mean whatever assets are needed to stop this outbreak. Assets could include providing more trained people engaged in actual control, not research, and more vocal support to elicit public active participation in Aedes aegypti control.

    If an investigation were conducted on the the public health response to this epidemic, would it show that everything that could be done to eliminate Aedes aegypti in this area was done by the public health community? Certainly i have read about all the efforts by the local mosquito control agency. However, was the response to this epidemic appropriate and the best effort that Key West, Monroe County, Florida and the U. S could mount. If it was then I agree with the post that this certainly shows the difficulty. But this is not San Juan Puerto Rico, not Bangkok Thailand, and thankfully not Miami, at least not yet This is Old Town Key West a 2X4 mile area with 6000 residents.

    Where is the publicity to engage the Key West public and business community in participating in the fight? Where are more resources to eliminate Aedes aegypti? Where is the public health community?

    However all the news reports I have seen on this outbreak shows that the response to the epidemic has been almost entirely due to the efforts of Florida Keys Mosquito Control. There has been virtually no “active” support provided by any other agencies to “interrupt” mosquito transmission. Yes press releases have been issued by health departments, but other than that, what other “aggressive” actions have been taken? Have they been successful? Why? What are the problems? Why is the Key West community, including many leaders, not participating according to press releases and statements in the Key West news media?

    The news coverage has been extensive in the national media, with unfortunately little impact at all on the residents of Key West who have not aggressively participated in an anti-Aedes aegypti campaign. Anyone familiar with Aedes aegypti control knows community engagment to eliminate larval habitats and take personal protection is essential to have a chance for success. Consider the public outreach efforts conducted in other dengue areas like Puerto Rico. Has this been done in Key West? Why not?

    I will leave this thread with one question. Is this the best that the U. S. can do in controlling a small focal dengue epidemic?

    Natural mosquito repellents are the way to go ! Don’t ever ever spray DEET repellent directly on your skin ! You can read more here:

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