Interactions between timing and transmissibility explain diverse flavivirus dynamics in Fiji.

Zika virus (ZIKV) has caused large, brief outbreaks in isolated populations, however ZIKV can also persist at low levels over multiple years. The reasons for these diverse transmission dynamics remain poorly understood. In Fiji, which has experienced multiple large single-season dengue epidemics, there was evidence of multi-year transmission of ZIKV between 2013 and 2017. To identify factors that could explain these differences in dynamics between closely related mosquito-borne flaviviruses, we jointly fit a transmission dynamic model to surveillance, serological and molecular data. We estimate that the observed dynamics of ZIKV were the result of two key factors: strong seasonal effects, which created an ecologically optimal time of year for outbreaks; and introduction of ZIKV after this optimal time, which allowed ZIKV transmission to persist over multiple seasons. The ability to jointly fit to multiple data sources could help identify a similar range of possible outbreak dynamics in other settings.

Sustained Low-Level Transmission of Zika and Chikungunya Viruses after Emergence in the Fiji Islands.

Zika and chikungunya viruses were first detected in Fiji in 2015. Examining surveillance and phylogenetic and serologic data, we found evidence of low-level transmission of Zika and chikungunya viruses during 2013-2017, in contrast to the major outbreaks caused by closely related virus strains in other Pacific Island countries.

Investigation of a Guillain-Barré syndrome cluster in the Republic of Fiji.

BACKGROUND: In 2014, we investigated a cluster of Guillain-Barre syndrome (GBS) in Fiji that occurred during a dengue epidemic. We designed a case-control study to determine the etiology. METHODS: Cases were patients meeting Brighton Collaboration criteria for GBS with onset from February 2014 to May 2014. Controls were persons without symptoms of GBS who were matched by age group and location. We collected information on demographics and potential exposures. Serum samples were tested for evidence of recent arboviral or Leptospira spp. infections. RESULTS: Nine cases of GBS were identified for an incidence of five cases per 100,000 population/year. Median age of cases was 27years (range: 0.8-52); five (56%) were male. Six (67%) reported an acute illness prior to GBS onset. Among the 9 cases and 28 controls enrolled, odds ratios for reported exposures or antibodies against various arboviruses or Leptospira spp. were not statistically significant. CONCLUSIONS: No clear etiologies were identified for this unusual GBS cluster. There was a temporal association between the GBS cluster and a dengue epidemic, but we were unable to substantiate an epidemiologic or laboratory association. Further study is needed to explore potential associations between arboviral infections and GBS.

Use of a Rapid Test for Diagnosis of Dengue during Suspected Dengue Outbreaks in Resource-Limited Regions.

Dengue is major public health problem, globally. Timely verification of suspected dengue outbreaks allows for public health response, leading to the initiation of appropriate clinical care. Because the clinical presentation of dengue is nonspecific, dengue diagnosis would benefit from a sensitive rapid diagnostic test (RDT). We evaluated the diagnostic performance of an RDT that detects dengue virus (DENV) nonstructural protein 1 (NS1) and anti-DENV IgM during suspected acute febrile illness (AFI) outbreaks in four countries. Real-time reverse transcription-PCR and anti-DENV IgM enzyme-linked immunosorbent assay were used to verify RDT results. Anti-DENV IgM RDT sensitivity and specificity ranged from 55.3 to 91.7% and 85.3 to 98.5%, respectively, and NS1 sensitivity and specificity ranged from 49.7 to 92.9% and 22.2 to 89.0%, respectively. Sensitivity varied by timing of specimen collection and DENV serotype. Combined test results moderately improved the sensitivity. The use of RDTs identified dengue as the cause of AFI outbreaks where reference diagnostic testing was limited or unavailable.