title: Quantifying the emergence of dengue in Hanoi, Vietnam: 1998-2009.
abstract: BACKGROUND
  An estimated 2.4 billion people live in areas at risk of dengue transmission, therefore the factors determining the establishment of endemic dengue in areas where transmission suitability is marginal is of considerable importance. Hanoi, Vietnam is such an area, and following a large dengue outbreak in 2009, we set out to determine if dengue is emerging in Hanoi.
  
  
  RESULTS
  We undertook a temporal and spatial analysis of 25,983 dengue cases notified in Hanoi between 1998 and 2009. Age standardized incidence rates, standardized age of infection, and Standardized Morbidity Ratios (SMR) were calculated. A quasi-Poisson regression model was used to determine if dengue incidence was increasing over time. Wavelet analysis was used to explore the periodicity of dengue transmission and the association with climate variables. After excluding the two major outbreak years of 1998 and 2009 and correcting for changes in population age structure, we identified a significant annual increase in the incidence of dengue cases over the period 1999-2008 (incidence rate ratio  =  1.38, 95% confidence interval  =  1.20-1.58, p value  =  0.002). The age of notified dengue cases in Hanoi is high, with a median age of 23 years (mean 26.3 years). After adjusting for changes in population age structure, there was no statistically significant change in the median or mean age of dengue cases over the period studied. Districts in the central, highly urban, area of Hanoi have the highest incidence of dengue (SMR>3).
  
  
  CONCLUSIONS
  Hanoi is a low dengue transmission setting where dengue incidence has been increasing year on year since 1999. This trend needs to be confirmed with serological surveys, followed by studies to determine the underlying drivers of this emergence. Such studies can provide insights into the biological, demographic, and environmental changes associated with vulnerability to the establishment of endemic dengue.
authors: Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Unit, Hanoi, Vietnam.
authors: Hoang Quoc
authors: HQ
authors: Cuong
authors: Nguyen Tran
authors: NT
authors: Hien
authors: Tran Nhu
authors: TN
authors: Duong
authors: Tran Vu
authors: TV
authors: Phong
authors: Nguyen Nhat
authors: NN
authors: Cam
authors: Jeremy
authors: J
authors: Farrar
authors: Vu Sinh
authors: VS
authors: Nam
authors: Khoa T D
authors: KT
authors: Thai
authors: Peter
authors: P
authors: Horby
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D021821:Communicable Diseases, Emerging / Q000453:epidemiology*; D003715:Dengue / Q000453:epidemiology*; D005260:Female; D005843:Geography; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D014744:Vietnam / Q000453:epidemiology; D055815:Young Adult