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

Results

During 2010–2020, a total of 30,903 cases were reported to ArboNET from American Samoa, Guam, Puerto Rico, and USVI; 21,705 (70.2%) were confirmed and 9,198 (29.8%) were probable (Table 1). The highest number of dengue cases occurred among persons aged <20 years, accounting for approximately half (15,640 [50.6%]) of reported cases. A majority of cases occurred in males, accounting for 16,808 (54.4%) of all cases. Approximately 2% (584) of all cases were categorized as severe dengue. A total of 10,037 (32.4%) persons with dengue were hospitalized, and 68 (0.2%) deaths were reported. Travel to a country with local transmission of dengue in the 2 weeks before symptom onset was reported in 28 (0.1%) cases.

Puerto Rico

During 2010–2020, the majority (29,862 [96.6%]) of dengue cases were reported from Puerto Rico (Figure 1). Annual incidence per 1,000 population was highest during the two outbreaks in 2010 and 2013, 2.9 and 2.6, respectively (Figure 2). Among all reported cases from Puerto Rico, 20,675 (69.2%) were confirmed and 9,187 (30.8%) were probable; 54.6% of dengue cases were in males. Approximately 50% of reported cases in Puerto Rico occurred among persons aged <20 years, with the 10–19-year-old age group accounting for 37.3% of cases. The highest incidence and hospitalization rates also occurred among children aged 10–14 and 15–19 years (Figure 3). In Puerto Rico, 32.6% of persons with dengue were hospitalized and 68 dengue-associated deaths were reported during 2010–2020; the highest number of deaths (n = 10) occurred among persons aged >70 years, although six (8.8%) of the deaths occurred among persons aged <20 years (Figure 4). Almost all (>99%) cases of dengue in Puerto Rico were locally acquired.

American Samoa

During 2010–2020, American Samoa accounted for 660 (2.1%) of all reported cases in the U.S. territories (Figure 1). Annual incidence per 1,000 population was highest in 2017, reaching 10.2 per 1,000 population (Figure 2). All dengue cases were confirmed, and 50.3% were in females. The highest case numbers and rates occurred among persons aged <20 years; 68.0% of reported cases occurred among persons aged <20 years, and 45.9% occurred among persons aged 10–19 years. The proportion of persons with dengue cases hospitalized in American Samoa (45.5%) was similar to Puerto Rico (Table 1); the highest incidence rates and hospitalizations occurred in the 10–14 and 15–19-year-old age groups (Figure 5). No dengue-associated deaths were reported, and one travel-associated case was reported.

U.S. Virgin Islands

During 2010–2020, USVI accounted for 353 (1.1%) of all reported cases in the U.S. territories (Figure 1). Annual incidence per 1,000 population was highest during the 2012–2013 outbreak with an annual incidence of 1.6 in 2013 (Figure 2). Almost all (96.9%) reported cases in USVI were confirmed, and 53.3% were in females. Approximately one third of reported cases occurred among children and adolescents aged <20 years, with a majority (21.5%) in the 10–19-year-old age group. The 20–29-year-old age group was the second most affected age group with 15.0% of cases. Three (0.8%) persons with dengue were hospitalized, and no dengue-associated deaths were reported. The highest incidence rate occurred among children aged 10–14 years (Figure 6). All reported cases were locally acquired.

Guam

During 2010–2020, Guam accounted for 28 (0.1%) of all reported cases in the U.S. territories. All cases were confirmed and occurred in 2019 and 2020; however, nearly one half of all reported cases (13 [46.4%]) were travel associated. More than one half (60.7%) of cases were in males. Similar to the other U.S. territories, the 10–19-year-old age group was most affected, with approximately 25% of reported cases. Unlike the other territories, the next most affected age group was persons aged 30–39 years, accounting for 21.4% of cases. Thirty-two percent of persons with dengue were hospitalized, and no dengue-associated deaths were reported (Table 1).

Serotype Distribution in Puerto Rico, USVI, and American Samoa

A total of 21,329 confirmed cases from Puerto Rico (21,194), USVI (119), and American Samoa (16) had DENV serotype data reported to or performed by the CDC Dengue Branch Laboratory (Table 2). In Puerto Rico, the majority (72.9%) of cases were DENV-1, followed by DENV-4 (24.1%), which were associated with the large dengue outbreaks during 2010–2013 (Figure 7). Concurrent with the emergence of chikungunya in 2014 and Zika in 2016, overall dengue case counts decreased from 2015 to 2019, with all four DENV serotypes circulating at low levels. In 2019 and 2020, dengue activity increased slightly, with all locally acquired cases identified as DENV-1, in addition to multiple travel-associated cases of DENV-2 and DENV-3. In USVI, DENV-1 and DENV-4 were the two circulating dengue serotypes during the outbreaks during 2012–2013, with DENV-1 accounting for 80.7% of cases with serotype available. In American Samoa, limited serotype data were available, although DENV-2 (n = 2) and DENV-3 (n = 14) cases were reported.