HIV Genetic Variation Influences Diagnostic Assay Performance

Increasing diversity of human immunodeficiency virus (HIV) strains is influencing the diagnostic capacity of viral load assays. This, in turn, affects the ability of clinicians to effectively monitor progress of anti-HIV drug therapies

Reports presented at the 16th Conference on Retroviruses and Opportunistic Infections (CROI) in Montreal on February 10, 2009, confirmed that there is a rising prevalence of Non-B HIV subtypes in the United States.

The Global HIV Surveillance Program at Abbott (Abbott Park, IL, USA) evaluated HIV-infected specimens using the Abbott RealTime HIV-1 test and the Roche (Indianapolis, IN, USA) Cobas Taqman HIV-1 test. The Abbott RealTime (RT) HIV assay quantified HIV more accurately than the Cobas Taqman assay in an analysis of 317 seropositive samples from seven countries: Argentina, Brazil, Cameroon, Saudi Arabia, South Africa, Thailand, and Uganda. The samples included six different HIV subtypes and eight circulating recombinant forms. Only 18 samples were subtype B, the most common HIV strain in the United States. The Taqman assay failed to detect five infected samples and under estimated viral load in 38 samples, compared to the Abbott assay.

A study performed by the University of Maryland School of Medicine (Baltimore, MD, USA) showed that the prevalence of non-subtype B strains in the Baltimore metro area is about two percent, based on tests of 2,200 HIV patients. However, in the Maryland portion of the Washington D.C. area, 13 % of the positive samples sequenced were non-B. The majority of non-B subtypes (80.8 %) were from recent immigrants from Africa.

Similar data presented by ARUP Laboratories (Salt Lake City, UT) showed that the prevalence of non-B subtypes increased steadily from 2004 through 2008 with incidences of non-B subtypes in 30 of 43 states. The most dramatic increases were seen for subtypes A and C.

The studies add to the growing body of evidence documenting the increasing spread of divergent HIV strains in the United States. The New England Journal of Medicine (NEJM) (April 10, 2008) reported: "The continuing spread of HIV is causing a world pandemic of unprecedented genetic and geographic complexity. Five HIV subtypes and two circulating recombinant forms have each established a global prevalence greater than 2.5%, a level that virtually ensures continued presence in the decades to come."

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