title: Pre-treatment mycobacterial sputum load influences individual on-treatment measurements.
abstract: Time to culture positivity (TTP) in liquid medium is now widely available as a measure of viable mycobacterial sputum load. TTP correlates well with and could replace colony-forming unit (CFU) counting in studies of antituberculosis drug effects. We investigated the influence of the pre-treatment mycobacterial sputum load on 4428 CFU measurements obtained within the first 14 days of treatment. Using a prediction model we show that pre-treatment CFU counts contribute 29% to the variation of on-treatment CFU counts and increase the precision of the prediction of on-treatment CFU from TTP by 12%. On the other hand, pre-treatment TTP contributed only 12% to the variation of on-treatment TTP and only added 2% to the prediction of TTP from CFU. We conclude pre-treatment measurements are covariates that can enhance the accuracy of statistical estimates of treatment effects, particularly when measured by CFU counts.
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Diacon
authors.forename: Lize
authors.initials: L
authors.lastname: van der Merwe
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Demers
authors.forename: Florian
authors.initials: F
authors.lastname: Von Groote-Bidlingmaier
authors.forename: Amour
authors.initials: A
authors.lastname: Venter
authors.forename: Peter R
authors.initials: PR
authors.lastname: Donald
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D055808:Drug Discovery / Q000379:methods; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D050296:Microbial Viability / Q000187:drug effects; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000302:isolation & purification*; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000382:microbiology*
chemical_list: D000995:Antitubercular Agents