Epidemiologic Trends of Dengue in U.S. Territories, 2010-2020.

Problem/condition: Dengue is one of the most common vectorborne flaviviral infections globally, with frequent outbreaks in tropical regions. In 2019 and 2020, the Pan American Health Organization reported approximately 5.5 million dengue cases from the Americas, the highest number on record. In the United States, local dengue virus (DENV) transmission has been reported from all U.S. territories, which are characterized by tropical climates that are highly suitable for Aedes species of mosquitoes, the vector that transmits dengue. Dengue is endemic in the U.S. territories of American Samoa, Puerto Rico, and the U.S. Virgin Islands (USVI). Dengue risk in Guam and the Commonwealth of the Northern Mariana Islands is considered sporadic or uncertain. Despite all U.S. territories reporting local dengue transmission, epidemiologic trends over time have not been well described.

Reporting period: 2010-2020.

Description of system: State and territorial health departments report dengue cases to CDC through ArboNET, the national arboviral surveillance system, which was developed in 2000 to monitor West Nile virus infections. Dengue became nationally notifiable in ArboNET in 2010. Dengue cases reported to ArboNET are categorized using the 2015 Council of State and Territorial Epidemiologists case definition. In addition, DENV serotyping is performed at CDC's Dengue Branch Laboratory in a subset of specimens to support identification of circulating DENV serotypes.

Results: During 2010-2020, a total of 30,903 dengue cases were reported from four U.S. territories to ArboNET. Puerto Rico reported the highest number of dengue cases (29,862 [96.6%]), followed by American Samoa (660 [2.1%]), USVI (353 [1.1%]), and Guam (28 [0.1%]). However, annual incidence rates were highest in American Samoa with 10.2 cases per 1,000 population in 2017, followed by Puerto Rico with 2.9 in 2010 and USVI with 1.6 in 2013. Approximately one half (50.6%) of cases occurred among persons aged <20 years. The proportion of persons with dengue who were hospitalized was high in three of the four territories: 45.5% in American Samoa, 32.6% in Puerto Rico, and 32.1% in Guam. In Puerto Rico and USVI, approximately 2% of reported cases were categorized as severe dengue. Of all dengue-associated deaths, 68 (0.2%) were reported from Puerto Rico; no deaths were reported from the other territories. During 2010-2020, DENV-1 and DENV-4 were the predominant serotypes in Puerto Rico and USVI.

Interpretation: U.S. territories experienced a high prevalence of dengue during 2010-2020, with approximately 30,000 cases reported, and a high incidence during outbreak years. Children and adolescents aged <20 years were disproportionately affected, highlighting the need for interventions tailored for this population. Ongoing education about dengue clinical management for health care providers in U.S. territories is important because of the high hospitalization rates reported. Dengue case surveillance and serotyping can be used to guide future control and prevention measures in these areas.

Public health action: The Advisory Committee on Immunization Practices recommends vaccination with Dengvaxia for children aged 9-16 years with evidence of previous dengue infection and living in areas where dengue is endemic. The recommendation for the dengue vaccine offers public health professionals and health care providers a new intervention for preventing illness and hospitalization in the age group with the highest burden of disease in the four territories (Paz Bailey G, Adams L, Wong JM, et al. Dengue Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2021. MMWR Recomm Rep 2021;70[No. RR-6]). American Samoa, Puerto Rico, and USVI are all considered endemic areas and persons residing in these areas are eligible for the new dengue vaccine. Persons aged 9-16 years in those jurisdictions with laboratory evidence of previous dengue infection can receive the dengue vaccine and benefit from a reduced risk for symptomatic disease, hospitalization, or severe dengue. Health care providers in these areas should be familiar with the eligibility criteria and recommendations for vaccination to reduce the burden of dengue among the group at highest risk for symptomatic illness. Educating health care providers about identification and management of dengue cases can improve patient outcomes and improve surveillance and reporting of dengue cases.