Dengue Fever Outbreak–Big Island, Hawaii 2015–2016

BACKGROUND: On October 21, 2015, the Hawaii Department of Health (HDOH) received notification of a positive dengue immunoglobulin M (IgM) antibody result for a Hawaii Island (Big Island) resident with no travel history but family members reporting similar illness. Subsequently, on October 24^th, we received a report of mainland US visitors, who had traveled together on the Big Island and several of whom had developed febrile illness consistent with dengue fever. We received an additional notification on October 27^th of an unrelated Big Island resident with a positive dengue IgM result. Given the presence of Aedes mosquitoes throughout the state, we launched an investigation to determine the scope of the outbreak and engaged with county partners in response and control activities.

METHODS:  Medical advisories were distributed on October 29^th and November 5^th to clinicians requesting they report any patients evaluated on or after September 1, 2015 for suspected dengue fever (acute onset fever and ≥2 of the following: headache and/or retro-orbital pain, nausea, myalgias and/or arthralgias, or generalized maculopapular rash). To find suspected dengue cases among Hawaii visitors, HDOH posted a call for cases on Epi-X. All suspect cases were interviewed with a standardized questionnaire; exposures were mapped to identify potential areas of disease transmission.  Laboratory testing was performed at the State Laboratories Division. A confirmed case was defined as having RT-PCR or serological evidence of recent dengue infection. Vector staff assessed and abated areas of residence and other potential mosquito exposure sites.

RESULTS: As of March 24, 2016, 263 laboratory-confirmed dengue fever cases have been identified (onset dates, September 11, 2015 through March 17, 2016). Fifty-one percent are male, and the median age is 35 years. A majority, 237 (90%), of the cases are Big Island residents; no cases have been identified on other islands in the state.  Thirty-seven (14%) of the cases required hospitalization; no severe dengue and no deaths have been reported. Dengue type 1 was identified in 186 (71%) cases. Response activities are ongoing. 

CONCLUSIONS: We report the largest dengue fever outbreak in Hawaii State since 1944. Dengue fever is not endemic in Hawaii. However, the frequency of global travel puts Hawaii at constant risk for dengue or other arboviral disease introduction. Assuring timely notification regarding suspect cases and immediate and aggressive coordinated epidemiological investigation and vector control activities are essential to prevent dengue fever or another arbovirus from establishing itself in Hawaii.