Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. CD4 decline in seroconverter and seroprevalent individuals in the precombination of antiretroviral therapy era Sara Lodi a , Andrew Phillips b , Giota Touloumi c , Nikos Pantazis c , Heiner C. Bucher d , Abdel Babiker a , Genevie `ve Che ˆne e , Philippe Vanhems f,g , Kholoud Porter a , on behalf of the CASCADE Collaboration M Background: Studies based on seroconverters have increased our understanding of HIV disease. It is not clear, however, whether their disease progression differs from that of the general HIV population, given their reasons for presenting for testing. Methods: Using linear mixed models we compared CD4 decline rates for a seroconverter (CASCADE) and seroprevalent group (Concorde trial) with time origin being dates of seroconversion and randomization, respectively. Follow-up was censored at the earlier of last alive date and 1 January 1996. Analyses were adjusted for risk group, age and sex. To explore the role of symptomatic seroconversion we further categorized seroconverters into two groups: with and without an HIV test interval below 30 days as proxy. Results: The 7226 seroconverter and 1746 seroprevalent eligible individuals were mainly men (78 and 85%, respectively) infected through sex between men (52 and 63%) with mean [95% confidence interval (CI)] baseline CD4 cell count of 610 (602, 619) and 492 (479, 505) cells/ml, respectively. There was no evidence that rate of CD4 decline differs between the two groups even after adjusting for potential confounders (P ¼ 0.67). Estimated loss in the year after reaching an arbitrary threshold of 400 cells/ml was 67 (95% CI 65, 69) and 67 (64, 69) cells/ml in the seroconverter and seroprevalent group, respectively. Whereas seroconverters with test interval below 30 days (n ¼ 310) experienced faster decline, there was no difference in rates between other serocon- verters and seroprevalent individuals (P ¼ 0.87). Conclusions: These data suggest that estimates of HIV progression derived from seroconverters are likely to hold more generally for the HIV-infected population. ß 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins AIDS 2010, 24:2697–2704 Keywords: CD4 decline, HIV, natural history, repeat testing, seroconverters, seroprevalent Introduction For a minority of HIV-infected individuals the date of HIV seroconversion can be well approximated due to the availability of a previous antibody negative HIV test, or because of the existence of laboratory test results indicative of acute infection. Studies based on such individuals, seroconverters, have provided much of our a MRC Clinical Trials Unit, b UCL Medical School, London, UK, c Athens University Medical School, Greece, d Basel Institute for Clinical Epidemiology & Biostatistics, University Hospital Basel, Switzerland, e Universite ´ Bordeaux II, f Edouard Herriot Hospital, Lyon, and g Universite ´ de Lyon 1, France. Correspondence to Dr Sara Lodi, MRC Clinical Trials Unit, 222 Euston Road, London NW12DA, UK. E-mail: sal@ctu.mrc.ac.uk  See Acknowledgement section. Received: 9 June 2010; revised: 22 July 2010; accepted: 27 July 2010. DOI:10.1097/QAD.0b013e32833ef6c4 ISSN 0269-9370 Q 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins 2697