A Differential Effect of Indian Ocean Dipole and El Niño on Cholera Dynamics in Bangladesh

Masahiro Hashizume,Kazuhiko Moji,Md Yunus,Luis Fernando Chaves,Kim Streatfield,A S G Faruque,Dongsheng Zhou

doi:10.1371/journal.pone.0060001

Abstract

BackgroundA stationary (i.e., constant through time) association between El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and epidemics of cholera in Bangladesh has been widely assumed. However, whether or not elements of the local climate that are relevant for cholera transmission have stationary signatures of the IOD on their dynamics over different time scales is still not clear. Here we report results on the time-varying relationships between the various remote and local environmental drivers and cholera incidence in Bangladesh.Methodology/Principal FindingsWe performed a cross wavelet coherency analysis to examine patterns of association between monthly cholera cases in the hospitals in Dhaka and Matlab (1983–2008) and indices for both IOD and ENSO. Our results showed that the strength of both the IOD and ENSO associations with cholera hospitalizations changed across time scales during the study period. In Dhaka, 4-year long coherent cycles were observed between cholera and the index of IOD in 1988–1997. In Matlab, the effect of ENSO was more dominant while there was no evidence for an IOD effect on cholera hospitalizations.Conclusions/SignificanceOur results call for the consideration of non-stationary, possibly non-linear, patterns of association between cholera hospitalizations and climatic factors in cholera epidemic early warning systems.

Highlights

Cholera remains a major public health problem in many places, including Bangladesh, India, and a number of countries in Africa and South America [1]
Our analyses indicated that the links between cholera hospitalizations and both Indian Ocean Dipole (IOD) and the El Nino Southern Oscillation (ENSO) were not consistent overtime and that the timing of the associations was different between urban Dhaka and rural Matlab
In Matlab, the effect of ENSO on cholera hospitalizations was more dominant; there was no similar evidence of an effect of IOD on cholera hospitalizations

Summary

Introduction

Cholera remains a major public health problem in many places, including Bangladesh, India, and a number of countries in Africa and South America [1]. It has been reported that the El Nino-Southern Oscillation (ENSO) plays a role in the interannual variation of endemic cholera in Bangladesh [6,8,9,10]. Sea surface temperature (SST) and sea surface height (SSH) in the Bay of Bengal have been proposed to influence the incidence of cholera in Dhaka [6,11,12,13]. A stationary (i.e., constant through time) association between El Nino Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and epidemics of cholera in Bangladesh has been widely assumed.

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Conclusion