title: Geospatial distribution and clustering of Chlamydia trachomatis in communities undergoing mass azithromycin treatment.
abstract: OBJECTIVE
  We detected spatial clustering of households with Chlamydia trachomatis infection (CI) and active trachoma (AT) in villages undergoing mass treatment with azithromycin (MDA) over time.
  
  
  METHODS
  We obtained global positioning system (GPS) coordinates for all households in four villages in Kongwa District, Tanzania. Every 6 months for a period of 42 months, our team examined all children under 10 for AT, and tested for CI with ocular swabbing and Amplicor. Villages underwent four rounds of annual MDA. We classified households as having ≥1 child with CI (or AT) or having 0 children with CI (or AT). We calculated the difference in the K function between households with and without CI or AT to detect clustering at each time point.
  
  
  RESULTS
  Between 918 and 991 households were included over the 42 months of this analysis. At baseline, 306 households (32.59%) had ≥1 child with CI, which declined to 73 households (7.50%) at 42 months. We observed borderline clustering of households with CI at 12 months after one round of MDA and statistically significant clustering with growing cluster sizes between 18 and 24 months after two rounds of MDA. Clusters diminished in size at 30 months after 3 rounds of MDA. Active trachoma did not cluster at any time point.
  
  
  CONCLUSIONS
  This study demonstrates that CI clusters after multiple rounds of MDA. Clusters of infection may increase in size if the annual antibiotic pressure is removed. The absence of growth after the three rounds suggests the start of control of transmission.
authors.affiliation: Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Jithin
authors.initials: J
authors.lastname: Yohannan
authors.affiliation: Bloomberg School of Public Health, Department of Biostatistics, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Bing
authors.initials: B
authors.lastname: He
authors.affiliation: Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Jiangxia
authors.initials: J
authors.lastname: Wang
authors.affiliation: Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Gregory
authors.initials: G
authors.lastname: Greene
authors.affiliation: Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Yvette
authors.initials: Y
authors.lastname: Schein
authors.affiliation: Kongwa Trachoma Project, Kongwa, Tanzania.
authors.forename: Harran
authors.initials: H
authors.lastname: Mkocha
authors.affiliation: Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Munoz
authors.affiliation: Division of Intramural Research, National Institute for Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Quinn
authors.affiliation: International Chlamydia Laboratory, Division of Infectious Diseases, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Gaydos
authors.affiliation: Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Sheila K
authors.initials: SK
authors.lastname: West
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D017963:Azithromycin / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D002692:Chlamydia trachomatis / Q000302:isolation & purification*; D019353:Endemic Diseases; D006801:Humans; D007223:Infant; D012424:Rural Population; D013029:Space-Time Clustering; D013636:Tanzania / Q000453:epidemiology; D014141:Trachoma / Q000188:drug therapy* / Q000453:epidemiology* / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D017963:Azithromycin
keywords: Chlamydia trachomatis; azithromycin; trachoma