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The U.S. territory of American Samoa has experienced recent outbreaks of illnesses caused by viruses transmitted by Aedes species mosquitoes, including dengue, chikungunya, and Zika virus. In November 2016, a traveler from the Solomon Islands tested positive for infection with dengue virus type 2 (DENV-2). Additional dengue cases were identified in the subsequent weeks through passive and active surveillance. Suspected dengue cases were tested locally with a dengue rapid diagnostic test (RDT) for DENV nonstructural protein 1 (NS1). Specimens from RDT-positive cases and patients meeting the dengue case definition were tested by real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) at Hawaii State Laboratories. During November 2016-October 2018, a total of 3,240 patients were tested for evidence of DENV infection (118 by RDT-NS1 alone, 1,089 by real-time RT-PCR alone, and 2,033 by both methods), 1,081 (33.4%) of whom tested positive for dengue (19.5 per 1,000 population). All 941 real-time RT-PCR-positive specimens were positive for DENV-2. The monthly number of laboratory-confirmed cases peaked at 120 during December 2017. Among laboratory-confirmed dengue cases, 380 (35.2%) patients were hospitalized; one patient, who was transferred to American Samoa for care late in his illness, died. The public health response to this outbreak included disposal of solid waste to remove mosquito breeding sites, indoor residual spraying of pesticides in schools, reinforcement of dengue patient management education, and public education on mosquito avoidance and seeking medical care for symptoms of dengue., Competing Interests: All authors have completed and submitted the ICMJE form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.

Cross-reactivity within flavivirus antibody assays, produced by shared epitopes in the envelope proteins, can complicate the serological diagnosis of Zika virus (ZIKAV) infection. We assessed the utility of the plaque reduction neutralization test (PRNT) to confirm recent ZIKAV infections and rule out misleading positive immunoglobulin M (IgM) results in areas with various levels of past dengue virus (DENV) infection incidence. We reviewed PRNT results of sera collected for diagnosis of ZIKAV infection from 1 January through 31 August 2016 with positive ZIKAV IgM results, and ZIKAV and DENV PRNTs were performed. PRNT result interpretations included ZIKAV, unspecified flavivirus, DENV infection, or negative. For this analysis, ZIKAV IgM was considered false positive for samples interpreted as a DENV infection or negative. In U.S. states, 208 (27%) of 759 IgM-positive results were confirmed to be ZIKAV compared to 11 (21%) of 52 in the U.S. Virgin Islands (USVI), 15 (15%) of 103 in American Samoa, and 13 (11%) of 123 in Puerto Rico. In American Samoa and Puerto Rico, more than 80% of IgM-positive results were unspecified flavivirus infections. The false-positivity rate was 27% in U.S. states, 18% in the USVI, 2% in American Samoa, and 6% in Puerto Rico. In U.S. states, the PRNT provided a virus-specific diagnosis or ruled out infection in the majority of IgM-positive samples. Almost a third of ZIKAV IgM-positive results were not confirmed; therefore, providers and patients must understand that IgM results are preliminary. In territories with historically higher rates of DENV transmission, the PRNT usually could not differentiate between ZIKAV and DENV infections., (This is a work of the U.S. Government and is not subject to copyright protection in the United States. Foreign copyrights may apply.)

On October 21, 2015, the Hawaii Department of Health (HDOH) was notified of a positive dengue immunoglobulin M (IgM) antibody result in a woman residing on Hawaii Island (also known as the Big Island). The patient had no history of travel off the island, and other family members reported having similar signs and symptoms, which consisted of fever, headache, myalgias and arthralgias, and a generalized erythematous rash. HDOH initiated an investigation to identify any additional cases and potential exposure sources. On October 24, HDOH received report of a group of mainland U.S. visitors who had traveled together on Hawaii Island, including several who had developed a febrile illness. Additionally, on October 27, HDOH was notified of an unrelated person, also on Hawaii Island, with a positive dengue IgM result. As of November 26, 2015, HDOH had identified 107 laboratory-confirmed cases of dengue fever, with dates of onset ranging from September 11 to November 18, 2015.