Virus-Specific Differences in Rates of Disease during the 2010 Dengue Epidemic in Puerto Rico.

Background: Dengue is a potentially fatal acute febrile illness (AFI) caused by four mosquito-transmitted dengue viruses (DENV-1–4) that are endemic in Puerto Rico. In January 2010, the number of suspected dengue cases reported to the passive dengue surveillance system exceeded the epidemic threshold and an epidemic was declared soon after. Methodology/Principal Findings: To characterize the epidemic, surveillance and laboratory diagnostic data were compiled. A suspected case was a dengue-like AFI in a person reported by a health care provider with or without a specimen submitted for diagnostic testing. Laboratory-positive cases had: (i) DENV nucleic acid detected by reverse transcriptase-polymerase chain reaction (RT-PCR) in an acute serum specimen; (ii) anti-DENV IgM antibody detected by ELISA in any serum specimen; or (iii) DENV antigen or nucleic acid detected in an autopsy-tissue specimen. In 2010, a total of 26,766 suspected dengue cases (7.2 per 1,000 residents) were identified, of which 46.6% were laboratory-positive. Of 7,426 RT-PCR-positive specimens, DENV-1 (69.0%) and DENV-4 (23.6%) were detected more frequently than DENV-2 (7.3%) and DENV-3 (<0.1%). Nearly half (47.1%) of all laboratory-positive cases were adults, 49.7% had dengue with warning signs, 11.1% had severe dengue, and 40 died. Approximately 21% of cases were primary DENV infections, and 1–4 year olds were the only age group for which primary infection was more common than secondary. Individuals infected with DENV-1 were 4.2 (95% confidence interval [CI]: 1.7–9.8) and 4.0 (95% CI: 2.4–6.5) times more likely to have primary infection than those infected with DENV-2 or -4, respectively. Conclusions/Significance: This epidemic was long in duration and yielded the highest incidence of reported dengue cases and deaths since surveillance began in Puerto Rico in the late 1960's. This epidemic re-emphasizes the need for more effective primary prevention interventions to reduce the morbidity and mortality of dengue. Author Summary: Dengue is a potentially fatal acute febrile illness that is endemic throughout the tropics and sub-tropics. Dengue has been endemic in Puerto Rico for several decades and recent epidemics occurred in 1994–5, 1998 and 2007. In January 2010, dengue surveillance indicated that an epidemic had begun. The epidemic peaked in early August and ended in December with a total of 26,766 suspected dengue cases identified, of which 128 were fatal. The 2010 epidemic was one of the longest in Puerto Rico history and resulted in the greatest number of cases and deaths ever detected. We analyzed the epidemiologic and immunologic characteristics of laboratory-confirmed dengue cases and age group-specific attack rates, and determined the frequency of first DENV infection and DENV-types among persons experiencing their first infection. This analysis indicated that 10–19 year-olds were most affected during the epidemic, and that DENV-1 was roughly four times more likely to be associated with clinically apparent illness upon first DENV infection than were DENV-2 or -4. The 2010 dengue epidemic demonstrated the heavy burden of illness due to dengue in Puerto Rico, re-emphasizing the critical need for effective primary prevention tools to reduce the morbidity and mortality due to dengue worldwide. [ABSTRACT FROM AUTHOR]

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