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Laboratory tests recommended for initial evaluation and follow-up of all patients are summarized in Table 2-15, pg 43.
HIV Types and Subtypes
HIV-1
HIV infection is established by detecting antibodies to the virus, viral antigens, viral RNA/DNA, or by culture (Lancet 1996;348:176). The standard test is serology for antibody detection. Two HIV types are HIV-1 and HIV-2, which show 40 to 60% aminoacid homology. HIV-1 accounts for nearly all cases except a minority of strains that originate in West Africa. HIV-1 is divided into subtypes designated A through K (collectively referred to as Group M with subtypes designated A, B, C, D, F, G, H, J and K and 15 circulating recombinant forms (CRFs) (AIDS 2000;14:S31). These CRFs include CRF01_AE (a mosaic with sequences from clades A and E), and CRF02_AG. Sub type O shows 55 to 70% homology with the M subtypes. Six strains account for most infections: subtype A, B, C, D and CRFs -- CRF01-AE and CRF02-AG (Table 2-1). Another group of viruses is labeled "N" for "new" first reported in 1998 (Nat Med 1998;4:1032; Science 2000;287:607). The O and N Groups are now thought to represent divergent evolution or distinctive cross-species transmission. Group O strains were once common in Cameroon, and HIV-2 was prominent in West Africa in the mid 1990's, but both have been largely displaced by HIV-1. Over 98% of HIV-1 infections in the United States are caused by subtype B; most non-B subtypes in the United States were acquired in other countries (JID 2000;181:470); the relatively rare O and N subtypes are still found primarily in West Africa. In a review of subtypes from 196 immigrants in New York City in 2005, subtype B accounted for 111 (55%), subtype A for 54 (27%), and subtype C for 8 (4%) (JID 2006;41:399).
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TABLE 2-1:
