US Dengue Cases Mostly Contracted Through Foreign Travel

Almost all of the US dengue cases from 2010 to 2017 were attributed to travel, specifically travel to the Caribbean and Asia, according to a report in the US Centers for Disease Control and Prevention (CDC’s) Morbidity and Mortality Weekly Report.

The CDC investigators used the national arboviral surveillance system (ArboNET) to review the total number of cases of dengue across all 50 states and Washington DC in order to track epidemiological trends in travel-associated as well as locally-acquired dengue cases. In 2010, dengue became a nationally notifiable disease, which means state and territorial health departments report cases to the CDC through ArboNET. The investigators, from the CDC’s Division of Vector-Borne Diseases, pulled the data from 2010 to 2017 for their study.

The number of dengue cases doubled each decade from 1990 to 2013 and reached a maximum of 390 million cases by 2010, the study authors reported. They added that approximately 13,600 people die from dengue every year and the geographic range for dengue is expected to increase as temperatures rise around the world.

“Local transmission of dengue in the United States is not common,” study author Aidsa Rivera, MS, epidemiologist at the CDC Dengue Branch, told Contagion®. “Though we do see occasional cases or outbreaks, most cases of dengue in the continental United States are reported in people who have been infected outside of the United States.”

Despite this, infected travelers can infect local mosquitoes if they are bit. The spread of dengue can then continue if infected mosquitos spread the virus to other people through more bites.

“Therefore, travelers who live in areas of the United States with Aedes aegypti mosquitoes should protect themselves from bites for three weeks after travel,” Rivera said.

During the investigation period, there were 5387 dengue cases reported to ArboNET, of which 93% were considered travel-associated. The remainder of the cases were locally-acquired, the study authors wrote. Approximately half of the infected patients were white, 14% were Asian, and the median patient age was 41 years. Dengue peaked with 961 cases in 2016 and the fewest number of cases, 254, was recorded in 2011.

About half of the travel-associated cases were reported from 4 states, New York (18%), California (16%), Florida (14%), and Texas (5%). Travel history was reported in nearly all of those cases, specifically to the Caribbean (33%) and Asia (29%), as well as Central America (14%), North America (10%), and South America (7%).

As for locally-acquired cases, Hawaii topped the charts with 250 cases of 66%. All of these Hawaii dengue cases were reported during an outbreak in 2015-16. Florida, Texas, and New York also reported dengue cases during the investigation period. Florida reported 2 small outbreaks: 2010 in Monroe County (56 cases) and 2013 in Martin County (17 cases). Texas had a small outbreak in 2013 with 21 cases in Cameron County, while New York had 1 case.

“Our findings highlight the importance of clinicians’ role in advising travelers of their risk and recognizing symptoms of dengue prevention upon their return,” Rivera continued. “Dengue is a potentially fatal disease and there is no readily available vaccine in the United States or treatment.”

The patients with dengue during the study period reported symptoms consistent with the infection, while less than 1% of either locally-acquired or travel-associated cases were considered severe.

Hospitalizations occurred in 40% of patients and almost all of those patients were travelers. There were 18 fatal dengue cases reported, all from travelers.

Travelers can check the CDC’s Traveler’s Health website before any travel for destination-specific information, including dengue risk, Rivera noted. Some preventative measures she suggested included an EPA-registered insect repellant, wearing long-sleeve shirts and long pants, staying in air-conditioned lodging when possible, or staying in places with screens.

“Health care providers should consider dengue in travelers returning with a non-specific acute febrile illness with nausea, vomiting, rash, myalgias, or arthralgias,” Rivera concluded.