title: Climatic-driven seasonality of emerging dengue fever in Hanoi, Vietnam.
abstract: BACKGROUND
  Dengue fever (DF) has been emerging in Hanoi over the last decade. Both DF epidemiology and climate in Hanoi are strongly seasonal. This study aims at characterizing the seasonality of DF in Hanoi and its links to climatic variables as DF incidence increases from year to year.
  
  
  METHODS
  Clinical suspected cases of DF from the 14 central districts of Hanoi were obtained from the Ministry of Health over a 8-year period (2002-2009). Wavelet decompositions were used to characterize the main periodic cycles of DF and climatic variables as well as the mean phase angles of these cycles. Cross-wavelet spectra between DF and each climatic variables were also computed. DF reproductive ratio was calculated from Soper's formula and smoothed to highlight both its long-term trend and seasonality.
  
  
  RESULTS
  Temperature, rainfall, and vapor pressure show strong seasonality. DF and relative humidity show both strong seasonality and a sub-annual periodicity. DF reproductive ratio is increasing through time and displays two clear peaks per year, reflecting the sub-annual periodicity of DF incidence. Temperature, rainfall and vapor pressure lead DF incidence by a lag of 8-10 weeks, constant through time. Relative humidity leads DF by a constant lag of 18 weeks for the annual cycle and a lag decreasing from 14 to 5 weeks for the sub-annual cycle.
  
  
  CONCLUSIONS
  Results are interpreted in terms of mosquito population dynamics and immunological interactions between the different dengue serotypes in the human compartment. Given its important population size, its strong seasonality and its dengue emergence, Hanoi offers an ideal natural experiment to test hypotheses on dengue serotypes interactions, knowledge of prime importance for vaccine development.
authors.affiliation: Biostatistics and Medical Informatics Department, Institute of Training for Preventive Medicine and Public Health, Hanoi Medical University, Hanoi, Vietnam. dothithanhtoan@hmu.edu.vn.
authors.forename: Thi Thanh Toan
authors.initials: TT
authors.lastname: Do
authors.forename: Pim
authors.initials: P
authors.lastname: Martens
authors.forename: Ngoc Hoat
authors.initials: NH
authors.lastname: Luu
authors.forename: Pamela
authors.initials: P
authors.lastname: Wright
authors.forename: Marc
authors.initials: M
authors.lastname: Choisy
mesh_terms: D002980:Climate; D057231:Climate Change; D021821:Communicable Diseases, Emerging / Q000453:epidemiology*; D003715:Dengue / Q000453:epidemiology*; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D014744:Vietnam / Q000453:epidemiology