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On April 24, 2023, the American Samoa Department of Health (ASDoH) declared a public health emergency amid concern about a possible measles outbreak given low 2-dose vaccination coverage at the time. ASDoH had received two positive measles immunoglobulin (Ig) M test results after Flag Day festivities 1 week earlier from vaccinated children. ASDoH performed active case finding, took actions to mitigate transmission, and requested technical assistance from CDC. ASDoH implemented a vaccination campaign to improve suboptimal coverage. Confirmatory molecular testing of specimens from these initial persons under investigation (PUIs) was not possible, but subsequent testing of specimens from additional PUIs by Hawaii State Laboratories Division and CDC ruled out measles. In settings with low measles prevalence, measles antibody testing results have low positive predictive value and can lead to difficulties with interpreting results. Testing for additional pathogens revealed a variety of viruses known to cause common childhood viral exanthems. Both molecular and serologic testing should be performed for all suspected measles cases. To decrease the probability of false-positive IgM results, testing should be reserved for cases that meet the Council of State and Territorial Epidemiologists measles case definition, especially those in persons with no evidence of immunity and with a history of recent international travel. In addition, maintaining high measles vaccination coverage can prevent future outbreaks.

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.

The first patients with laboratory-confirmed cases of Zika virus disease in American Samoa had symptom onset in January 2016 (1). In response, the American Samoa Department of Health (ASDoH) implemented mosquito control measures (1), strategies to protect pregnant women (1), syndromic surveillance based on electronic health record (EHR) reports (1), Zika virus testing of persons with one or more signs or symptoms of Zika virus disease (fever, rash, arthralgia, or conjunctivitis) (1-3), and routine testing of all asymptomatic pregnant women in accordance with CDC guidance (2,3) All collected blood and urine specimens were shipped to the Hawaii Department of Health Laboratory for Zika virus testing and to CDC for confirmatory testing. Early in the response, collection and testing of specimens from pregnant women was prioritized over the collection from symptomatic nonpregnant patients because of limited testing and shipping capacity. The weekly numbers of suspected Zika virus disease cases declined from an average of six per week in January-February 2016 to one per week in May 2016. By August, the EHR-based syndromic surveillance (1) indicated a return to pre-outbreak levels. The last Zika virus disease case detected by real-time, reverse transcription-polymerase chain reaction (rRT-PCR) occurred in a patient who had symptom onset on June 19, 2016. In August 2016, ASDoH requested CDC support in assessing whether local transmission had been reduced or interrupted and in proposing a timeline for discontinuation of routine testing of asymptomatic pregnant women. An end date (October 15, 2016) was determined for active mosquito-borne transmission of Zika virus and a timeline was developed for discontinuation of routine screening of asymptomatic pregnant women in American Samoa (conception after December 10, 2016, with permissive testing for asymptomatic women who conceive through April 15, 2017).

During December 2015-January 2016, the American Samoa Department of Health (ASDoH) detected through surveillance an increase in the number of cases of acute febrile rash illness. Concurrently, a case of laboratory-confirmed Zika virus infection, a mosquito-borne flavivirus infection documented to cause microcephaly and other severe brain defects in some infants born to women infected during pregnancy (1,2) was reported in a traveler returning to New Zealand from American Samoa. In the absence of local laboratory capacity to test for Zika virus, ASDoH initiated arboviral disease control measures, including public education and vector source reduction campaigns. On February 1, CDC staff members were deployed to American Samoa to assist ASDoH with testing and surveillance efforts.

During December 2015-January 2016, the American Samoa Department of Health (ASDoH) detected through surveillance an increase in the number of cases of acute febrile rash illness. Concurrently, a case of laboratory-confirmed Zika virus infection, a mosquito-borne flavivirus infection documented to cause microcephaly and other severe brain defects in some infants born to women infected during pregnancy was reported in a traveler returning to New Zealand from American Samoa. In the absence of local laboratory capacity to test for Zika virus, ASDoH initiated arboviral disease control measures, including public education and vector source reduction campaigns. On February 1, CDC staff members were deployed to American Samoa to assist ASDoH with testing and surveillance efforts. To track the progression of the outbreak in the absence of confirmed case results, trends in the number of suspected Zika virus disease cases were monitored through syndromic surveillance using automated searches of the electronic health record system at the one hospital and four health care clinics in the territory.

American Samoa has experienced multiple outbreaks of mosquitoborne viral disease in recent years, including chikun...gunya in 2014, dengue in 2015, and Zika in 2016. During November 2016-October 2018, 1,081 laboratory-confirmed dengue cases were identified, with only dengue virus type 2 detected. The epidemic peaked in December 2017, after which, case counts slowly decreased. Sustainable, effective interventions are still needed to control dengue, as is continued emphasis on clinical management to reduce mortality. Persons residing in or traveling to areas with risk for dengue should use insect repellent, wear long sleeves and pants, and stay in residences with screens on doors and windows.

During December 2015-January 2016, the American Samoa Department of Health (ASDoH) detected through surveillance an increase in the number of cases of acute febrile rash illness. Concurrently, a case of laboratory-confirmed Zika virus infection, a mosquito-borne flavivirus infection documented to cause microcephaly and other severe brain defects in some infants born to women infected during pregnancy was reported in a traveler returning to New Zealand from American Samoa. In the absence of local laboratory capacity to test for Zika virus, ASDoH initiated arboviral disease control measures, including public education and vector source reduction campaigns. On February 1, CDC staff members were deployed to American Samoa to assist ASDoH with testing and surveillance efforts. To track the progression of the outbreak in the absence of confirmed case results, trends in the number of suspected Zika virus disease cases were monitored through syndromic surveillance using automated searches of the electronic health record system at the one hospital and four health care clinics in the territory.

The first patients with laboratory-confirmed cases of Zika virus disease in American Samoa had symptom onset in January 2016. In response, the American Samoa Department of Health (ASDoH) implemented mosquito control measures, strategies to protect pregnant women, syndromic surveillance based on electronic health record (EHR) reports, Zika virus testing of persons with one or more signs or symptoms of Zika virus disease (fever, rash, arthralgia, or conjunctivitis), and routine testing of all asymptomatic pregnant women in accordance with CDC guidance. All collected blood and urine specimens were shipped to the Hawaii Department of Health Laboratory for Zika virus testing and to CDC for confirmatory testing. Early in the response, collection and testing of specimens from pregnant women was prioritized over the collection from symptomatic nonpregnant patients because of limited testing and shipping capacity. The weekly numbers of suspected Zika virus disease cases declined from an average of six per week in January-February 2016 to one per week in May 2016.