title: An index of community ocular Chlamydia trachomatis load for control of trachoma.
abstract: Quantitative PCR (Q-PCR) technology has recently been applied to the measurement of ocular loads of Chlamydia trachomatis. We present an index called the community ocular C. trachomatis load (COCTL) which is similar to the community microfilarial load (CMFL) of onchocerciasis. Our index has the advantage of being scale-independent so that, for example, percentage changes are the same whether calculated per eye swab or per Q-PCR capillary. The COCTL for a population or subgroup is formed by adding the arbitrary concentration of 1 organism per ml to each individual Q-PCR quantification, calculating the geometric mean, and finally subtracting 1 per ml again. The use of the COCTL is illustrated in a study of trachoma in northern Tanzania. The COCTL is higher in people with clinical trachoma than those without (5.8 organisms per swab vs. 0.1), and in children aged six months to ten years than in the overall population (1.1 vs. 0.4). The COCTL index is potentially useful for sentinel sites, operational research and calibration of clinical measures of trachoma.
authors.affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK. neal.alexander@lshtm.ac.uk
authors.forename: N D E
authors.initials: ND
authors.lastname: Alexander
authors.forename: A W
authors.initials: AW
authors.lastname: Solomon
authors.forename: M J
authors.initials: MJ
authors.lastname: Holland
authors.forename: R L
authors.initials: RL
authors.lastname: Bailey
authors.forename: S K
authors.initials: SK
authors.lastname: West
authors.forename: J F
authors.initials: JF
authors.lastname: Shao
authors.forename: D C W
authors.initials: DC
authors.lastname: Mabey
authors.forename: A
authors.initials: A
authors.lastname: Foster
mesh_terms: D000284:Administration, Oral; D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D017963:Azithromycin / Q000008:administration & dosage; D002648:Child; D002675:Child, Preschool; D002692:Chlamydia trachomatis / Q000302:isolation & purification*; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D016133:Polymerase Chain Reaction / Q000379:methods; D012720:Severity of Illness Index; D013636:Tanzania / Q000453:epidemiology; D014141:Trachoma / Q000453:epidemiology / Q000382:microbiology* / Q000517:prevention & control
chemical_list: D000900:Anti-Bacterial Agents; D017963:Azithromycin