title: Cholera and shigellosis: different epidemiology but similar responses to climate variability.
abstract: BACKGROUND
  Comparative studies of the associations between different infectious diseases and climate variability, such as the El Niño-Southern Oscillation, are lacking. Diarrheal illnesses, particularly cholera and shigellosis, provide an important opportunity to apply a comparative approach. Cholera and shigellosis have significant global mortality and morbidity burden, pronounced differences in transmission pathways and pathogen ecologies, and there is an established climate link with cholera. In particular, the specific ecology of Vibrio cholerae is often invoked to explain the sensitivity of that disease to climate.
  
  
  RESULTS
  The extensive surveillance data of the International Center for Diarrheal Disease Research, Bangladesh are used here to revisit the known associations between cholera and climate, and to address their similarity to previously unexplored patterns for shigellosis. Monthly case data for both the city of Dhaka and a rural area known as Matlab are analyzed with respect to their association with El Niño and flooding. Linear correlations are examined between flooding and cumulative cases, as well as for flooding and El Niño. Rank-correlation maps are also computed between disease cases in the post-monsoon epidemic season and sea surface temperatures in the Pacific. Similar climate associations are found for both diseases and both locations. Increased cases follow increased monsoon flooding and increased sea surface temperatures in the preceding winter corresponding to an El Niño event.
  
  
  CONCLUSIONS
  The similarity in association patterns suggests a systemic breakdown in population health with changing environmental conditions, in which climate variability acts primarily through increasing the exposure risk of the human population. We discuss these results in the context of the on-going debate on the relative importance of the environmental reservoir vs. secondary transmission, as well as the implications for the use of El Niño as an early indicator of flooding and enteric disease risk.
authors.affiliation: Center for Ocean-Land-Atmosphere Studies, Fairfax, Virginia, United States of America.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Cash
authors.affiliation: Institut Català de Ciències del Clima (IC3), Barcelona, Catalunya, Spain; Institució Catalana de Recerca i Estudis Avançats, Barcelona, Catalunya, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Rodó
authors.affiliation: University of North Carolina Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Emch
authors.affiliation: International Centre for Diarrheal Disease Research, Dhaka, Bangladesh.
authors.forename: Md
authors.initials: M
authors.lastname: Yunus
authors.affiliation: International Centre for Diarrheal Disease Research, Dhaka, Bangladesh.
authors.forename: Abu S G
authors.initials: AS
authors.lastname: Faruque
authors.affiliation: Department of Ecology and Evolutionary Biology University of Michigan, Ann Arbor, Michigan, United States of America; Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Pascual
mesh_terms: D001459:Bangladesh / Q000453:epidemiology; D002771:Cholera / Q000453:epidemiology*; D002980:Climate; D004196:Disease Outbreaks; D004405:Dysentery, Bacillary / Q000453:epidemiology*; D055868:Floods; D006801:Humans; D011159:Population Surveillance; D012621:Seasons; D012623:Seawater; D013696:Temperature; D014734:Vibrio cholerae