title: CT694 and pgp3 as serological tools for monitoring trachoma programs.
abstract: BACKGROUND
  Defining endpoints for trachoma programs can be a challenge as clinical signs of infection may persist in the absence of detectable bacteria. Antibody-based tests may provide an alternative testing strategy for surveillance during terminal phases of the program. Antibody-based assays, in particular ELISAs, have been shown to be useful to document C. trachomatis genital infections, but have not been explored extensively for ocular C. trachomatis infections.
  
  
  RESULTS
  An antibody-based multiplex assay was used to test two C. trachomatis antigens, pgp3 and CT694, for detection of trachoma antibodies in bloodspots from Tanzanian children (n = 160) collected after multiple rounds of mass azithromycin treatment. Using samples from C. trachomatis-positive (by PCR) children from Tanzania (n = 11) and control sera from a non-endemic group of U.S. children (n = 122), IgG responses to both pgp3 and CT694 were determined to be 91% sensitive and 98% specific. Antibody responses of Tanzanian children were analyzed with regard to clinical trachoma, PCR positivity, and age. In general, children with more intense ocular pathology (TF/TI = 2 or most severe) had a higher median antibody response to pgp3 (p = 0.0041) and CT694 (p = 0.0282) than those with normal exams (TF/TI = 0). However, 44% of children with no ocular pathology tested positive for antibody, suggesting prior infection. The median titer of antibody responses for children less than three years of age was significantly lower than those of older children. (p<0.0001 for both antigens).
  
  
  CONCLUSIONS
  The antibody-based multiplex assay is a sensitive and specific additional tool for evaluating trachoma transmission. The assay can also be expanded to include antigens representing different diseases, allowing for a robust assay for monitoring across NTD programs.
authors.affiliation: Division of Parasitic Diseases and Malaria, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: E Brook
authors.initials: EB
authors.lastname: Goodhew
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Priest
authors.forename: Delynn M
authors.initials: DM
authors.lastname: Moss
authors.forename: Guangming
authors.initials: G
authors.lastname: Zhong
authors.forename: Beatriz
authors.initials: B
authors.lastname: Munoz
authors.forename: Harran
authors.initials: H
authors.lastname: Mkocha
authors.forename: Diana L
authors.initials: DL
authors.lastname: Martin
authors.forename: Sheila K
authors.initials: SK
authors.lastname: West
authors.forename: Charlotte
authors.initials: C
authors.lastname: Gaydos
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Lammie
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D000907:Antibodies, Bacterial / Q000097:blood*; D000942:Antigens, Bacterial / Q000276:immunology*; D017963:Azithromycin / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007223:Infant; D008219:Lymphogranuloma Venereum / Q000175:diagnosis / Q000188:drug therapy*; D008297:Male; D012680:Sensitivity and Specificity; D013636:Tanzania
chemical_list: D000900:Anti-Bacterial Agents; D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C550863:CT694 protein, Chlamydia trachomatis; D007074:Immunoglobulin G; C082169:pgp3 protein, Chlamydia; D017963:Azithromycin