title: The incubation period to AIDS in injecting drug users estimated from prevalent cohort data, accounting for death prior to an AIDS diagnosis.
abstract: OBJECTIVE
  To estimate the incubation-period distribution (time from seroconversion to AIDS) accounting for death before an AIDS diagnosis (DBAD) in a cohort of injecting drug users (IDU) in Amsterdam, The Netherlands and to compare these estimates with those previously obtained from a contemporaneous study of homosexual and bisexual men in Amsterdam carried out using the same facilities.
  
  
  METHODS
  Participants in a cohort study begun in Amsterdam at the end of 1985 have scheduled follow-up visits every 4 months. All participants of Dutch nationality and who had two or more follow-up visits before January 1996 from which CD4 measurements were available were included in this study. Data concerning AIDS diagnosis and death were verified through review of national and municipal registries.
  
  
  METHODS
  Because time of seroconversion was unknown for study participants and because IDU are at substantial risk for DBAD, we used a Markov model with CD4-based stages that allows for DBAD. The parameters in this model were estimated using the method of maximum likelihood and confidence intervals were calculated using bootstrap methods.
  
  
  RESULTS
  A total of 173 IDU (134 seroprevalent, 39 seroincident) made 1829 visits. Nearly 10% of the visits were non-consecutive. Forty-five IDU developed AIDS and 25 died without an AIDS diagnosis. We estimated that 24% [95% confidence interval (CI), 17-25%] of IDU die before an AIDS diagnosis. As a result, the median time from seroconversion to AIDS (10.5 years; 95% CI, 9.1-10.7 years) is considerably longer than the median time from seroconversion to death (8.3 years; 95% CI, 7.9-8.5 years). Conditional on survival to an AIDS diagnosis, the median time to AIDS is 8.2 years (95% CI, 7.7-8.7 years). The median survival time after a diagnosis of AIDS is estimated to be 1.0 years.
  
  
  CONCLUSIONS
  The high occurrence of DBAD in IDU has a considerable influence on estimates of the incubation-period distribution. Progression from seroconversion to death was faster in the IDU cohort than in a cohort of homosexual men in Amsterdam (median, 8.3 years and 9.6 years, respectively). However, progression to AIDS conditional on survival to an AIDS diagnosis seems to be similar in both the IDU cohort and in the cohort of homosexual men (median, 8.2 years and 8.3 years, respectively).
authors.affiliation: Department of Public Health, Municipal Health Service, Amsterdam, The Netherlands.
authors.forename: J C
authors.initials: JC
authors.lastname: Hendriks
authors.forename: G A
authors.initials: GA
authors.lastname: Satten
authors.forename: E J
authors.initials: EJ
authors.lastname: van Ameijden
authors.forename: H A
authors.initials: HA
authors.lastname: van Druten
authors.forename: R A
authors.initials: RA
authors.lastname: Coutinho
authors.forename: G J
authors.initials: GJ
authors.lastname: van Griensven
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology*; D000328:Adult; D018791:CD4 Lymphocyte Count; D002423:Cause of Death; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D006679:HIV Seropositivity / Q000453:epidemiology*; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D008390:Markov Chains; D008875:Middle Aged; D012042:Registries; D015819:Substance Abuse, Intravenous / Q000150:complications*; D013997:Time Factors