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Notes from the Field: Dengue Epidemic --- Puerto Rico, January--July 2010

During January 1--July 15, 2010, a total of 6,321 suspected dengue cases were reported to the Puerto Rico Department of Health (PRDH) and CDC's Dengue Branch Passive Dengue Surveillance System, compared with 2,711 cases reported during the same period in 2009. The increase in cases began in January. In late February, when the number of reported cases exceeded the epidemic threshold for 2 consecutive weeks, PRDH declared a dengue epidemic. Dengue has been endemic in Puerto Rico for 4 decades (1). Although the timing of the current epidemic is unusually early (in Puerto Rico, increases in dengue cases typically occur during the June--November rainy season), the number of cases reported is large, and comparable to the 6,428 cases reported for the same period during a substantial epidemic in 1998 (2).

Of the 6,321 suspected cases, 2,831 (45%) have been laboratory-confirmed. During January--July 2010, the incidence of confirmed dengue was 74.3 cases per 100,000 population, with 35% of patients hospitalized and five deaths reported, all in adults. Incidence of laboratory-confirmed cases was highest among children aged 10--14 years (165 cases per 100,000), 15--19 years (163), and 5--9 years (91), followed by infants (83), and adults aged 20--24 years (77). The epidemic is widespread; of 78 municipalities in Puerto Rico, 72 had confirmed cases in June. Of the 2,831 laboratory-confirmed cases, 2,001 cases (71%) were positive by dengue virus (DENV) real-time reverse transcription--polymerase chain reaction (RT-PCR); 830 were positive for anti-DENV immunoglobulin M. Among RT-PCR positive cases, DENV-1 serotype (1,505) and DENV-4 (344) were detected more frequently than DENV-2 (150) and DENV-3 (two).

Large, island-wide epidemics occur every 3--5 years in Puerto Rico; in the most recent (2007), 10,508 suspected cases were reported (3). Abnormally high ambient temperature might be a factor in the high incidence in 2010, and, more importantly, a large proportion of the population might be susceptible to the predominant DENV-1 and DENV-4 serotypes (3). PRDH and CDC Dengue Branch are working with municipal leadership to raise awareness about prevention measures and eliminate mosquito production sites, and are providing continuing medical education on dengue clinical management and educational materials for patients.

Reported by

L Gonzalez Feliciano, MD, C Deseda, MD, Puerto Rico Dept of Health. A Rivera, MS, KM Tomashek, MD, J Munoz-Jordan, PhD, E Hunsperger, PhD, O Padro, LM Santiago, MPH, E Soto, MPH, J Perez, R Rodriguez, PhD, H Seda, MPH, R Barrera, PhD, DF Arguello, MD, H Margolis, MD, Dengue Br, CDC.


  1. Likosky WH, Calisher CH, Michelson AL, Correa-Coronas R, Henderson BE, Feldman RA. An epidemiologic study of dengue type 2 in Puerto Rico, 1969. Am J Epidemiol 1973;97:264--75.
  2. Rigau-Perez JG, Ayala-Lopez A, Garcia-Rivera EJ, et al. The reappearance of dengue-3 and a subsequent dengue-4 and dengue-1 epidemic in Puerto Rico in 1998. Am J Trop Med Hyg 2002;67:355--62.
  3. Tomashek KM, Rivera A, Munoz JL, et al. Description of a large island-wide outbreak of dengue in Puerto Rico, 2007. Am J Trop Med Hyg 2009:81:467--74.

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