title: Geographic Information System and tools of spatial analysis in a pneumococcal vaccine trial.
abstract: BACKGROUND
  The goal of this Geographic Information System (GIS) study was to obtain accurate information on the locations of study subjects, road network and services for research purposes so that the clinical outcomes of interest (e.g., vaccine efficacy, burden of disease, nasopharyngeal colonization and its reduction) could be linked and analyzed at a distance from health centers, hospitals, doctors and other important services. The information on locations can be used to investigate more accurate crowdedness, herd immunity and/or transmission patterns.
  
  
  METHODS
  A randomized, placebo-controlled, double-blind trial of an 11-valent pneumococcal conjugate vaccine (11PCV) was conducted in Bohol Province in central Philippines, from July 2000 to December 2004. We collected the information on the geographic location of the households (N = 13,208) of study subjects. We also collected a total of 1982 locations of health and other services in the six municipalities and a comprehensive GIS data over the road network in the area.
  
  
  RESULTS
  We calculated the numbers of other study subjects (vaccine and placebo recipients, respectively) within the neighborhood of each study subject. We calculated distances to different services and identified the subjects sharing the same services (calculated by distance). This article shows how to collect a complete GIS data set for human to human transmitted vaccine study in developing country settings in an efficient and economical way.
  
  
  CONCLUSIONS
  The collection of geographic locations in intervention trials should become a routine task. The results of public health research may highly depend on spatial relationships among the study subjects and between the study subjects and the environment, both natural and infrastructural.
  
  
  BACKGROUND
  ISRCTN: ISRCTN62323832.
authors.affiliation: Research Institute for Tropical Medicine, Muntinlupa City, Philippines. leilanitn@yahoo.com.
authors.forename: Antti
authors.initials: A
authors.lastname: Tanskanen
authors.forename: Leilani T
authors.initials: LT
authors.lastname: Nillos
authors.forename: Antti
authors.initials: A
authors.lastname: Lehtinen
authors.forename: Hanna
authors.initials: H
authors.lastname: Nohynek
authors.forename: Diozele Hazel M
authors.initials: DH
authors.lastname: Sanvictores
authors.forename: Eric Af
authors.initials: EA
authors.lastname: Simões
authors.forename: Veronica L
authors.initials: VL
authors.lastname: Tallo
authors.forename: Marilla G
authors.initials: MG
authors.lastname: Lucero