Abstract
Dengue is a potentially fatal acute febrile illness caused by four mosquito-transmitted dengue viruses (DENV-1–4). Although dengue outbreaks regularly occur in many regions of the Pacific, little is known about dengue in the Republic of the Marshall Islands (RMI). To better understand dengue in RMI, we investigated an explosive outbreak that began in October 2011. Suspected cases were reported to the Ministry of Health, serum specimens were tested with a dengue rapid diagnostic test (RDT), and confirmatory testing was performed using RT-PCR and IgM ELISA. Laboratory-positive cases were defined by detection of DENV nonstructural protein 1 by RDT, DENV nucleic acid by RT-PCR, or anti-DENV IgM antibody by RDT or ELISA. Secondary infection was defined by detection of anti-DENV IgG antibody by ELISA in a laboratory-positive acute specimen. During the four months of the outbreak, 1,603 suspected dengue cases (3% of the RMI population) were reported. Of 867 (54%) laboratory-positive cases, 209 (24%) had dengue with warning signs, six (0.7%) had severe dengue, and none died. Dengue incidence was highest in residents of Majuro and individuals aged 10–29 years, and ∼95% of dengue cases were experiencing secondary infection. Only DENV-4 was detected by RT-PCR, which phylogenetic analysis demonstrated was most closely related to a virus previously identified in Southeast Asia. Cases of vertical DENV transmission, and DENV/Salmonella Typhi and DENV/Mycobacterium leprae co-infection were identified. Entomological surveys implicated water storage containers and discarded tires as the most important development sites for Aedes aegypti and Ae. albopictus, respectively. Although this is the first documented dengue outbreak in RMI, the age groups of cases and high prevalence of secondary infection demonstrate prior DENV circulation. Dengue surveillance should continue to be strengthened in RMI and throughout the Pacific to identify and rapidly respond to future outbreaks.
Highlights
Dengue is the most common mosquito-borne viral illness in the world, and is endemic throughout the tropics and subtropics where,96 million cases occurred in 2010 [1,2]
The epidemiologic characteristics of this outbreak were captured by improving public and clinical awareness of dengue, enhancing surveillance to enable rapid case reporting, and use of a rapid diagnostic test (RDT) followed by confirmatory testing to define dengue cases
Pertinent findings include 3% of all Republic of the Marshall Islands (RMI) residents being reported as a suspected dengue case, laboratory confirmation of dengue in 3% of Majuro residents, hospitalization of 13% of dengue cases, and identification of water storage containers as prominent sources of vector mosquitoes
Summary
Dengue is the most common mosquito-borne viral illness in the world, and is endemic throughout the tropics and subtropics where ,96 million cases occurred in 2010 [1,2]. Infection with any of four dengue viruses (DENV-1–4), which are transmitted by select Aedes species mosquitoes, can result in dengue, an acute febrile illness characterized by headache, body pain, retro-orbital pain, rash and leukopenia [2]. Recent dengue outbreaks have been reported in the Pacific islands, including Fiji [5], Palau [6], Kiribati [7], the Federated. Travel between the Pacific islands and dengue-endemic countries throughout the region facilitates DENV circulation, which may result in outbreaks [7]. After an apparent absence of circulation in the Pacific Islands for many years, DENV-4 was detected in the region in 2008 and caused several outbreaks soon after [7,14]
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