title: A dengue outbreak on a floating village at Cat Ba Island in Vietnam.
abstract: BACKGROUND
  A dengue outbreak in an ecotourism destination spot in Vietnam, from September to November 2013, impacted a floating village of fishermen on the coastal island of Cat Ba. The outbreak raises questions about how tourism may impact disease spread in rural areas.
  
  
  METHODS
  Epidemiological data were obtained from the Hai Phong Preventive Medical Center (PMC), including case histories and residential location from all notified dengue cases from this outbreak. All household addresses were geo-located. Knox test, a spatio-temporal analysis that enables inference dengue clustering constrained by space and time, was performed on the geocoded locations. From the plasma available from two patients, positive for Dengue serotype 3 virus (DENV3), the Envelope (E) gene was sequenced, and their genetic relationships compared to other E sequences in the region.
  
  
  RESULTS
  Of 192 dengue cases, the odds ratio of contracting dengue infections for people living in the floating villages compared to those living on the island was 4.9 (95 % CI: 3.6-6.7). The space-time analyses on 111 geocoded dengue residences found the risk of dengue infection to be the highest within 4 days and a radius of 20 m of a given case. Of the total of ten detected clusters with an excess risk greater than 2, the cluster with the highest number of cases was in the floating village area (24 patients for a total duration of 31 days). Phylogenetic analysis revealed a high homology of the two DENV3 strains (genotype III) from Cat Ba with DENV3 viruses circulating in Hanoi in the same year (99.1 %).
  
  
  CONCLUSIONS
  Our study showed that dengue transmission is unlikely to be sustained on Cat Ba Island and that the 2013 epidemic likely originated through introduction of viruses from the mainland, potentially Hanoi. These findings suggest that prevention efforts should be focused on mainland rather than on the island.
authors.affiliation: Oxford University Clinical Research Unit Hanoi, Hanoi, Vietnam. thanhlv@oucru.org.
authors.forename: Thanh
authors.initials: T
authors.lastname: Le Viet
authors.affiliation: Oxford University Clinical Research Unit Hanoi, Hanoi, Vietnam. mchoisy@gmail.com.|MIVEGEC (University of Montpellier, CNRS 5290, IRD 224), Montpellier, France. mchoisy@gmail.com.
authors.forename: Marc
authors.initials: M
authors.lastname: Choisy
authors.affiliation: Oxford University Clinical Research Unit Hanoi, Hanoi, Vietnam. jbryant@oucru.org.|Nuffield Department of Clinical Medicine, Centre for Tropical Medicine, University of Oxford, Oxford, United Kingdom. jbryant@oucru.org.
authors.forename: Juliet E
authors.initials: JE
authors.lastname: Bryant
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam. vu.duoc@gmail.com.
authors.forename: Duoc
authors.initials: D
authors.lastname: Vu Trong
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam. phamquangthai@gmail.com.
authors.forename: Thai
authors.initials: T
authors.lastname: Pham Quang
authors.affiliation: Oxford University Clinical Research Unit Hanoi, Hanoi, Vietnam. peter.horby@gmail.com.|Nuffield Department of Clinical Medicine, Centre for Tropical Medicine, University of Oxford, Oxford, United Kingdom. peter.horby@gmail.com.
authors.forename: Peter
authors.initials: P
authors.lastname: Horby
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam. nthiennihe@vnn.vn.
authors.forename: Hien
authors.initials: H
authors.lastname: Nguyen Tran
authors.affiliation: Oxford University Clinical Research Unit Hanoi, Hanoi, Vietnam. huongttk@oucru.org.
authors.forename: Huong
authors.initials: H
authors.lastname: Tran Thi Kieu
authors.affiliation: National Hospital of Tropical Diseases, Hanoi, Vietnam. nvutrung@fpt.vn.
authors.forename: Trung
authors.initials: T
authors.lastname: Nguyen Vu
authors.affiliation: National Hospital of Tropical Diseases, Hanoi, Vietnam. kinhnv@nhtd.vn.
authors.forename: Kinh
authors.initials: K
authors.lastname: Nguyen Van
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam. lom9@hotmail.com.
authors.forename: Mai
authors.initials: M
authors.lastname: Le Quynh
authors.affiliation: Oxford University Clinical Research Unit Hanoi, Hanoi, Vietnam. heiman.wertheim@gmail.com.|Nuffield Department of Clinical Medicine, Centre for Tropical Medicine, University of Oxford, Oxford, United Kingdom. heiman.wertheim@gmail.com.|Radboudumc, Nijmegen, Netherlands. heiman.wertheim@gmail.com.
authors.forename: Heiman F L
authors.initials: HF
authors.lastname: Wertheim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D003715:Dengue / Q000453:epidemiology*; D003716:Dengue Virus; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010802:Phylogeny; D012424:Rural Population / Q000706:statistics & numerical data; D062211:Spatio-Temporal Analysis; D014744:Vietnam / Q000453:epidemiology; D055815:Young Adult