title: How reliable is an undetectable viral load?
abstract: OBJECTIVE
  An article by the Swiss AIDS Commission states that patients with stably suppressed viraemia [i.e. several successive HIV-1 RNA plasma concentrations (viral loads, VL) below the limits of detection during 6 months or more of highly active antiretroviral therapy (HAART)] are unlikely to be infectious. Questions then arise: how reliable is the undetectability of the VL, given the history of measures? What factors determine reliability?
  
  
  METHODS
  We assessed the probability (henceforth termed reliability) that the n+1 VL would exceed 50 or 1000 HIV-1 RNA copies/mL when the nth one had been <50 copies/mL in 6168 patients of the Swiss HIV Cohort Study who were continuing to take HAART between 2003 and 2007. General estimating equations were used to analyse potential factors of reliability.
  
  
  RESULTS
  With a cut-off at 50 copies/mL, reliability was 84.5% (n=1), increasing to 94.5% (n=5). Compliance, the current type of HAART and the first antiretroviral therapy (ART) received (HAART or not) were predictive factors of reliability. With a cut-off at 1000 copies/mL, reliability was 97.5% (n=1), increasing to 99.1% (n=4). Chart review revealed that patients had stopped their treatment, admitted to major problems with compliance or were taking non-HAART ART in 72.2% of these cases. Viral escape caused by resistance was found in 5.6%. No explanation was found in the charts of 22.2% of cases.
  
  
  CONCLUSIONS
  After several successive VLs at <50 copies/mL, reliability reaches approximately 94% with a cut-off of 50 copies/mL and approximately 99% with a cut-off at 1000 copies/mL. Compliance is the most important factor predicting reliability.
authors.affiliation: Division of Clinical Epidemiology, University Hospital Geneva, Geneva, Switzerland. christophe.combescure@hcuge.ch
authors.forename: Christophe
authors.initials: C
authors.lastname: Combescure
authors.forename: N
authors.initials: N
authors.lastname: Vallier
authors.forename: B
authors.initials: B
authors.lastname: Ledergerber
authors.forename: M
authors.initials: M
authors.lastname: Cavassini
authors.forename: H
authors.initials: H
authors.lastname: Furrer
authors.forename: A
authors.initials: A
authors.lastname: Rauch
authors.forename: M
authors.initials: M
authors.lastname: Battegay
authors.forename: E
authors.initials: E
authors.lastname: Bernasconi
authors.forename: P
authors.initials: P
authors.lastname: Vernazza
authors.forename: B
authors.initials: B
authors.lastname: Hirschel
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000627:therapeutic use*; D023241:Antiretroviral Therapy, Highly Active / Q000379:methods; D018791:CD4 Lymphocyte Count; D015331:Cohort Studies; D024882:Drug Resistance, Viral; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000276:immunology / Q000635:transmission / Q000821:virology; D015497:HIV-1 / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D055118:Medication Adherence; D008875:Middle Aged; D015999:Multivariate Analysis; D011336:Probability; D012367:RNA, Viral / Q000097:blood; D015203:Reproducibility of Results; D013557:Switzerland; D019562:Viral Load / Q000187:drug effects / Q000379:methods*; D014766:Viremia / Q000175:diagnosis* / Q000821:virology
chemical_list: D019380:Anti-HIV Agents; D012367:RNA, Viral