In 2009 there were 27 confirmed cases of Dengue Fever that originated in Key West, FL according to the May 21, 2010 issue of Morbidity and Mortality Weekly Report (MMWR) put out by the Center for Disease Control (CDC). Dengue Fever is one of those tropical diseases generally passed off by US physicians as exotic problems we really don’t need to think much about in the US. From 1946 until 1980 there were no diagnosed cases of Dengue felt to have been acquired in the US. Since then there have been only a few cases in areas on the Texas- US border associated with outbreaks in neighboring Mexican cities. (1)
In September 2010 a case of Dengue was diagnosed in New York City in a patient who had travelled only to Key West, FL. I very diligent and astute primary physician and an infectious disease consultant considered Dengue when a clinical picture very consistent with this disease was noted despite no history of travel to areas felt to be endemic. This was followed by numerous other cases of Key West residents and visitors.
In medical school we learned about all sorts of exotic tropical diseases. Except for one case of malaria I diagnosed as a fourth year student I have never made a diagnosis of any of these diseases. I still remember this case. I did my own thick prep and presented the case to my intern before he saw the patient, and felt pretty sharp. I didn’t tell him that the patient told me he had malaria, I just was open enough to believe him. Since then thoughts about most of these diseases have been relegated to some distant back shelf of my brain and to the occasional patient who comes in to prepare for international travel. I suspect this is the same for most US physicians. Well at least in Key West a disease not encountered in the US for decades has made enough of a presence to possibly be a reservoir of disease that could be tough to eradicate.
Dengue Fever is the most prevalent mosquito born disease in the world, affecting 50-100 million persons annually. Most cases are subclinical, meaning the patient does not get sick enough to seek medical attention or even feel sick. Still about 25,000 people annually die of Dengue. Death usually occurs as a result of overwhelming hemorrhagic disease. There is no known specific treatment for Dengue, and no immunization, so prevention relies primarily on mosquito control and mosquito bite avoidance. The CDC recommends using DEET on clothing as a repellent, using long sleeved and long pant-leg clothing that are bite resistant, and screens on housing in areas where mosquito borne disease like Dengue are prevalent.
The amazing thing about the Key West outbreak is that serologic testing by the CDC shows that about 5% of Key West residents contacted Dengue virus, showing IgM antibodies (signifying recent infection) on serologic survey testing. Obviously the majority of Key West residents who were infected has subclinical infections.
In the CDC article they summarize by saying:
The timely reporting of dengue in the index patient from New York illustrates that, despite an absence of compatible travel history, clinicians throughout the United States should consider appropriate laboratory testing based upon clinical presentation. Had the index patient not been evaluated promptly and reported, the cases in Key West residents likely would not have been diagnosed. Dengue should be included in the differential diagnosis of acute febrile illnesses for patients who live in or have recently traveled to subtropical areas in the United States or to the tropics. This is particularly important when signs and symptoms such as thrombocytopenia, leukopenia, hemoconcentration, rash, or eye pain are present. Prompt reporting of suspected dengue cases to public health authorities can facilitate a coordinated response resulting in detection of locally acquired cases or helping to define new areas of transmission. Additional information regarding dengue prevention, diagnosis, and management is available at http://www.cdc.gov/dengue.