title: Early participation in an HIV cohort study slows disease progression and improves survival. The Swiss HIV Cohort Study.
abstract: BACKGROUND
  Different levels of experience of physicians caring for patients with HIV infection have been found to be associated with differences in survival amongst their patients. We examined whether early participation in the Swiss HIV Cohort Study (SHCS), an ongoing prospective study with regular follow-up visits at specialized clinics, improved survival of HIV-infected patients.
  
  
  METHODS
  We studied 3553 HIV-infected individuals who joined the Swiss HIV Cohort Study (SHCS) with different levels of immunosuppression: mild (CD4 count above 500 x 106 cells L-1; n x 2038); severe (100-199 cells; n = 960); and very severe (50-99 cells; n = 555). Characteristics at different CD4 cell levels were compared and Cox proportional hazards regression was used to examine the mortality experience during a total of 16 201 person-years of follow-up.
  
  
  RESULTS
  Participants joining the cohort early with mild immunodeficiency were younger, more likely to be female, and more likely to have a history of intravenous drug use. At CD4 cell counts below 200 x 106 cells L-1, they were less likely to have a history of Pneumocystis carinii pneumonia or AIDS, more likely to be on prophylaxis against P. carinii and more likely to be on antiretroviral therapy than those joining with severe or very severe immunodeficiency. For example, at the time of the first CD4 cell count in the range of 50-99 x 106 cells L-1, 8.9, 15.0 and 21.6% of participants who joined with mild, severe and very severe immunodeficiency had suffered an episode of P. carinii pneumonia. In Cox models adjusted for CD4 cell count at entry and other relevant baseline differences, mortality was increased amongst participants who joined with severe and very severe immunodeficiency. Hazard ratios (95% confidence intervals (CI)) were 1.71 (1.21-2.42) for participants with severe immunodeficiency at entry and 2.61 (1.70-4. 01) for those with very severe immunodeficiency, compared with 1.0 for those with mild immunodeficiency at entry.
  
  
  CONCLUSIONS
  Individuals who were seen regularly at specialized HIV units from early stages of the infection onwards were, at comparable levels of immunodeficiency, less likely to progress to AIDS, and mortality during subsequent follow-up was reduced. This is likely to be explained by better access to prophylactic regimens and antiretroviral therapy.
authors.affiliation: Outpatient Department of Internal Medicine, University Hospital of Basel, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Battegay
authors.forename: M
authors.initials: M
authors.lastname: Wirz
authors.forename: M H
authors.initials: MH
authors.lastname: Steuerwald
authors.forename: M
authors.initials: M
authors.lastname: Egger
mesh_terms: D000328:Adult; D018791:CD4 Lymphocyte Count; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D015658:HIV Infections / Q000401:mortality*; D006801:Humans; D008297:Male; D016016:Proportional Hazards Models; D011446:Prospective Studies; D013557:Switzerland / Q000453:epidemiology