title: Effects of weather factors on dengue fever incidence and implications for interventions in Cambodia.
abstract: BACKGROUND
  Dengue viruses and their mosquito vectors are sensitive to their environment. Temperature, rainfall and humidity have well-defined roles in the transmission cycle. Therefore changes in these conditions may contribute to increasing incidence. The aim of this study was to examine the relationship between weather factors and dengue incidence in three provinces in Cambodia, in order to strengthen the evidence basis of dengue control strategies in this high-burden country.
  
  
  METHODS
  We developed negative binomial models using monthly average maximum, minimum, mean temperatures and monthly cumulative rainfall over the period from January 1998 to December 2012. We adopted piecewise linear functions to estimate the incidence rate ratio (IRR) between dengue incidence and weather factors for simplicity in interpreting the coefficients. We estimated the values of parameters below cut-points defined in terms of the results of sensitivity tests over a 0-3 month lagged period.
  
  
  RESULTS
  Mean temperature was significantly associated with dengue incidence in all three provinces, but incidence did not correlate well with maximum temperature in Banteay Meanchey, nor with minimum temperature in Kampong Thom at a lag of three months in the negative binomial model. The monthly cumulative rainfall influence on the dengue incidence was significant in all three provinces, but not consistently over a 0-3 month lagged period. Rainfall significantly affected the dengue incidence at a lag of 0 to 3 months in Siem Reap, but it did not have an impact at a lag of 2 to 3 months in Banteay Meanchey, nor at a lag of 2 months in Kampong Thom.
  
  
  CONCLUSIONS
  The association between dengue incidence and weather factors also apparently varies by locality, suggesting that a prospective dengue early warning system would likely be best implemented at a local or regional scale, rather than nation-wide in Cambodia. Such spatial down-scaling would also enable dengue control measures to be better targeted, timed and implemented.
authors.affiliation: World Health Organization, Phnom Penh, Cambodia. dudwh7@naver.com.
authors.forename: Youngjo
authors.initials: Y
authors.lastname: Choi
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Choon Siang
authors.initials: CS
authors.lastname: Tang
authors.affiliation: Australian National University, Canberra, Australia.
authors.forename: Lachlan
authors.initials: L
authors.lastname: McIver
authors.affiliation: Nagasaki University, Nagasaki, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hashizume
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Vibol
authors.initials: V
authors.lastname: Chan
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Rabindra Romauld
authors.initials: RR
authors.lastname: Abeyasinghe
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Steven
authors.initials: S
authors.lastname: Iddings
authors.affiliation: National Center for Parasitology, Entomology & Malaria Control, Phnom Penh, Cambodia.
authors.forename: Rekol
authors.initials: R
authors.lastname: Huy
mesh_terms: D002160:Cambodia / Q000453:epidemiology; D003715:Dengue / Q000453:epidemiology* / Q000517:prevention & control; D006801:Humans; D006813:Humidity; D015994:Incidence; D015233:Models, Statistical; D011446:Prospective Studies; D011891:Rain; D013696:Temperature; D014887:Weather