title: When can antibiotic treatments for trachoma be discontinued? Graduating communities in three African countries.
abstract: BACKGROUND
  Repeated mass azithromycin distributions are effective in controlling the ocular strains of chlamydia that cause trachoma. However, it is unclear when treatments can be discontinued. Investigators have proposed graduating communities when the prevalence of infection identified in children decreases below a threshold. While this can be tested empirically, results will not be available for years. Here we use a mathematical model to predict results with different graduation strategies in three African countries.
  
  
  METHODS
  A stochastic model of trachoma transmission was constructed, using the parameters with the maximum likelihood of obtaining results observed from studies in Tanzania (with 16% infection in children pre-treatment), The Gambia (9%), and Ethiopia (64%). The expected prevalence of infection at 3 years was obtained, given different thresholds for graduation and varying the characteristics of the diagnostic test.
  
  
  RESULTS
  The model projects that three annual treatments at 80% coverage would reduce the mean prevalence of infection to 0.03% in Tanzanian, 2.4% in Gambian, and 12.9% in the Ethiopian communities. If communities graduate when the prevalence of infection falls below 5%, then the mean prevalence at 3 years with the new strategy would be 0.3%, 3.9%, and 14.4%, respectively. Graduations reduced antibiotic usage by 63% in Tanzania, 56% in The Gambia, and 11% in Ethiopia.
  
  
  CONCLUSIONS
  Models suggest that graduating communities from a program when the infection is reduced to 5% is a reasonable strategy and could reduce the amount of antibiotic distributed in some areas by more than 2-fold.
authors.affiliation: F.I. Proctor Foundation, University of California, San Francisco, California, United States of America.
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Ray
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Lietman
authors.forename: Travis C
authors.initials: TC
authors.lastname: Porco
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Keenan
authors.forename: Robin L
authors.initials: RL
authors.lastname: Bailey
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Solomon
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Burton
authors.forename: Emma
authors.initials: E
authors.lastname: Harding-Esch
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Holland
authors.forename: David
authors.initials: D
authors.lastname: Mabey
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D017963:Azithromycin / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D002692:Chlamydia trachomatis / Q000187:drug effects*; D004363:Drug Utilization / Q000592:standards*; D005002:Ethiopia / Q000453:epidemiology; D005260:Female; D005714:Gambia / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D008962:Models, Theoretical; D015995:Prevalence; D013636:Tanzania / Q000453:epidemiology; D014141:Trachoma / Q000188:drug therapy* / Q000453:epidemiology*
chemical_list: D000900:Anti-Bacterial Agents; D017963:Azithromycin