On Jan. 14, 2016, Hawaii’s Civil Defense Agency closed all traffic to the Waipio Valley Access Road on the island of Hawaii and limited access to residents in the valley area in response to an ongoing dengue fever epidemic. This followed previous similar actions at other sites on the island.

On Feb. 8, 2015, Billy Kenoi, the mayor of Hawaii County (coterminous with the island of Hawaii — the “Big Island”), declared a state of emergency in response to the largest outbreak of dengue fever in Hawaii in seven decades. Four days later, David Ige, the governor of the state of Hawaii, followed suit, declaring a state of emergency to fight mosquito-borne illnesses, including dengue fever and the Zika virus. While there had been no locally transmitted cases of Zika virus, there had been a total of 255 confirmed cases of dengue fever in 231 Hawaii residents and 24 travelers to the state. Adults older than 18 years of age accounted for 209 of the total. The first case had onset of illness on Sept. 11, 2015.

Aedes aegypti, the dominant vector of human dengue virus infection, has limited geographic distribution in Hawaii, while a second dengue virus vector, Aedes albopictus — the Asian tiger mosquito — is present throughout the islands. Both mosquitoes bite during daytime hours and breed in small pools of water, both natural and man-made. The size and location of these pools, as well as other factors, account for the fact that mosquito control measures have apparently never been demonstrated to abort outbreaks.

Dengue is not endemic in Hawaii, but outbreaks have occurred previously, such as the most recent one in 2001-2002 when the virus was introduced by travelers from Tahiti, resulting in 122 laboratory-confirmed cases in Maui, Oahu, and Kauai. The current large outbreak is obviously worrisome with regard to the health of residents and visitors (approximately 12,000 visitors spend the night on the island of Hawaii each day). While almost 10% (24/255) of cases in the current outbreak occurred in visitors, an analysis after the 2001-2002 occurrence concluded that there was little risk to visitors.

The outbreak can be explained, in part, by the shortsightedness of funding decisions by state government, which, in response to the “Great Recession,” reduced the size of the state’s mosquito control and entomology staff from 56 in 2009 to 25 in 2016. Somehow they never noticed that the economic downturn had ended. At the invitation of the governor, CDC performed an extensive evaluation of the outbreak and the response to it. The evaluation concluded that the state’s responses had been excellent but that the outbreak had “revealed critical deficiencies in communications and medical entomologic capacities within the Department of Health that should be urgently addressed.”