title: The Indian Ocean dipole and cholera incidence in Bangladesh: a time-series analysis.
abstract: BACKGROUND
  It has been reported that the El Niño-Southern Oscillation (ENSO) influences the interannual variation of endemic cholera in Bangladesh. There is increased interest in the influence of the Indian Ocean dipole (IOD), a climate mode of coupled ocean-atmosphere variability, on regional ocean climate in the Bay of Bengal and on Indian monsoon rainfall.
  
  
  OBJECTIVE
  We explored the relationship between the IOD and the number of cholera patients in Bangladesh, controlling for the effects of ENSO.
  
  
  METHODS
  Time-series regression was performed. Negative binomial models were used to estimate associations between the monthly number of hospital visits for cholera in Dhaka and Matlab (1993-2007) and the dipole mode index (DMI) controlling for ENSO index [NINO3, a measure of the average sea surface temperature (SST) in the Niño 3 region], seasonal, and interannual variations. Associations between cholera cases and SST and sea surface height (SSH) of the northern Bay of Bengal were also examined.
  
  
  RESULTS
  A 0.1-unit increase in average DMI during the current month through 3 months before was associated with an increase in cholera incidence of 2.6% [(95% confidence interval (CI), 0.0-5.2; p = 0.05] in Dhaka and 6.9% (95% CI, 3.2-10.8; p < 0.01) in Matlab. Cholera incidence in Dhaka increased by 2.4% (95% CI, 0.0-5.0; p = 0.06) after a 0.1-unit decrease in DMI 4-7 months before. Hospital visits for cholera in both areas were positively associated with SST 0-3 months before, after adjusting for SSH (p < 0.01).
  
  
  CONCLUSIONS
  These findings suggest that both negative and positive dipole events are associated with an increased incidence of cholera in Bangladesh with varying time lags.
authors.affiliation: Institute of Tropical Medicine and Global Center of Excellence Program, Nagasaki University, Nagasaki, Japan. hashizum@nagasaki-u.ac.jp
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hashizume
authors.forename: A S G
authors.initials: AS
authors.lastname: Faruque
authors.forename: Toru
authors.initials: T
authors.lastname: Terao
authors.forename: Md
authors.initials: M
authors.lastname: Yunus
authors.forename: Kim
authors.initials: K
authors.lastname: Streatfield
authors.forename: Taro
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Moji
mesh_terms: D001459:Bangladesh / Q000453:epidemiology; D002771:Cholera / Q000453:epidemiology*; D006801:Humans; D019156:Indian Ocean / Q000453:epidemiology