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  • by routine serologic testing are pooled into 200-μl aliquots to create a master pool of 90 specimens from 9 pools of 10 specimens. A positive RT-PCR tests in the master pool then prompts testing of the contributing 10-sample pools and then the individual samples (JAMA 2002;288:216). Positive results are confirmed. In North Carolina, use of this method took 14 days and the cost was $2.01 per specimen. The test was used for contact tracing , since acute HIV has been associated with high rates of transmission (JID 2005;191:1403). Application of the test for one year in North Carolina included tests of 109,250 persons, of whom 606 were seropositive and 23 had acute HIV infection. A subsequent report for 2002 to 2007 indicated detection of 89 with acute HIV infection; 67 contacts were tested, and there were 11 newly detected cases. This equates to about 2 per year (McCoy S. CROI, 2008; Abstract #531).
  • Prognosis: Viral load correlates with the rate of CD4 decline or CD4 slope (JID 2002;185:908), but this association is not as strong as once thought (JAMA 2006;296:1523). The most comprehensive study to assess the association between viral load and natural history is the analysis of stored sera from the Multicenter AIDS Cohort Study (MACS), which found a strong association between “set point” and rate of progression that was independent of the baseline CD4 count (Ann Intern Med 1995;122:573; Science 1996;272:1167; JID 1996;174:696; JID 1996;174:704; AIDS 1999;13:1305; NEJM 2001;349,720; AIDS 2002;16:2455; Lancet 2003;362:679; JAIDS 2005;38:289). This has changed in the HAART era, when outcome is determined by therapy and is less dependent on baseline VL (AIDS 20 06;20:1197; CID 2006;42:136; JID 2004;190: 280). Even without HAART the CD4 slope appears to be influenced by other factors that influence immune activation (Nat Med 2006;12:1365).A strong association is supported by the rapid CD4 decline the accompanies rapid return of viremia to pretreatment levels when HAART is discontinued (NEJM 2003;349:837) and the sustained normal CD4 levels in "elite controllers" (JID 2008;197:563).
  • Risk of opportunistic infection: The VL appears to predict OIs independently of CD4 count when counts are <200 cells/mm3 (JAMA 1996;276:105; AIDS 1999;13:341; AIDS 1999;13:1035; JAIDS 2001;27:44), JID 2006; 194:633 The major prospective study examining this association was ACTG 722, which found that the failure to decrease VL by ≥1 log10 c/mL in patients with a baseline CD4 count of <150 cells/mm3 increased the risk of an OI 15-fold (JAIDS 2002;30:154). A retrospective review of over 12,000 patients showed that CD4 counts are the best predictors of progression to an AIDS-defining complication (Lancet 2002;360:119).
  • Probability of transmission: The probability of HIV transmission with nearly any type of exposure is directly correlated with viral load (NEJM 2000;342:921; JAIDS 1996;12:427;

 

2007 © John G. Bartlett, M.D. All rights reserved.20

Chapter 2: Laboratory Tests

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