title: The spatial dynamics of dengue virus in Kamphaeng Phet, Thailand.
abstract: BACKGROUND
  Dengue is endemic to the rural province of Kamphaeng Phet, Northern Thailand. A decade of prospective cohort studies has provided important insights into the dengue viruses and their generated disease. However, as elsewhere, spatial dynamics of the pathogen remain poorly understood. In particular, the spatial scale of transmission and the scale of clustering are poorly characterized. This information is critical for effective deployment of spatially targeted interventions and for understanding the mechanisms that drive the dispersal of the virus.
  
  
  RESULTS
  We geocoded the home locations of 4,768 confirmed dengue cases admitted to the main hospital in Kamphaeng Phet province between 1994 and 2008. We used the phi clustering statistic to characterize short-term spatial dependence between cases. Further, to see if clustering of cases led to similar temporal patterns of disease across villages, we calculated the correlation in the long-term epidemic curves between communities. We found that cases were 2.9 times (95% confidence interval 2.7-3.2) more likely to live in the same village and be infected within the same month than expected given the underlying spatial and temporal distribution of cases. This fell to 1.4 times (1.2-1.7) for individuals living in villages 1 km apart. Significant clustering was observed up to 5 km. We found a steadily decreasing trend in the correlation in epidemics curves by distance: communities separated by up to 5 km had a mean correlation of 0.28 falling to 0.16 for communities separated between 20 km and 25 km. A potential explanation for these patterns is a role for human movement in spreading the pathogen between communities. Gravity style models, which attempt to capture population movement, outperformed competing models in describing the observed correlations.
  
  
  CONCLUSIONS
  There exists significant short-term clustering of cases within individual villages. Effective spatially and temporally targeted interventions deployed within villages may target ongoing transmission and reduce infection risk.
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; Faculty of Public Health, Mahidol University, Bangkok, Thailand.
authors.forename: Piraya
authors.initials: P
authors.lastname: Bhoomiboonchoo
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Robert V
authors.initials: RV
authors.lastname: Gibbons
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Angkana
authors.initials: A
authors.lastname: Huang
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: In-Kyu
authors.initials: IK
authors.lastname: Yoon
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Darunee
authors.initials: D
authors.lastname: Buddhari
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Ananda
authors.initials: A
authors.lastname: Nisalak
authors.affiliation: Faculty of Public Health, Mahidol University, Bangkok, Thailand.
authors.forename: Natkamol
authors.initials: N
authors.lastname: Chansatiporn
authors.affiliation: Faculty of Public Health, Mahidol University, Bangkok, Thailand.
authors.forename: Mathuros
authors.initials: M
authors.lastname: Thipayamongkolgul
authors.affiliation: Queen Sirikit National Institute of Child Health, Bangkok, Thailand.
authors.forename: Siripen
authors.initials: S
authors.lastname: Kalanarooj
authors.affiliation: Department of Infectious Diseases, State University of New York, Syracuse, New York, United States of America.
authors.forename: Timothy
authors.initials: T
authors.lastname: Endy
authors.affiliation: University of Rhode Island, Providence, Rhode Island, United States of America.
authors.forename: Alan L
authors.initials: AL
authors.lastname: Rothman
authors.affiliation: Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
authors.forename: Anon
authors.initials: A
authors.lastname: Srikiatkhachorn
authors.affiliation: Center for Infectious Disease and Vaccine Research, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
authors.forename: Sharone
authors.initials: S
authors.lastname: Green
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Mammen P
authors.initials: MP
authors.lastname: Mammen
authors.affiliation: Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.
authors.forename: Derek A
authors.initials: DA
authors.lastname: Cummings
authors.affiliation: Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.
authors.forename: Henrik
authors.initials: H
authors.lastname: Salje
mesh_terms: D016000:Cluster Analysis; D003715:Dengue / Q000453:epidemiology* / Q000821:virology; D003716:Dengue Virus / Q000302:isolation & purification*; D062306:Geography, Medical; D006801:Humans; D062206:Spatial Analysis; D013785:Thailand / Q000453:epidemiology