1238. A 4th Generation Antigen/Antibody Combination Assay-based HIV Testing Algorithm Using HIV-1 NAAT for Confirmation Detects a High Proportion of HIV Infections
Session: Oral Abstract Session: HIV: Detection, Linkage, and Utilization
Saturday, October 5, 2013: 10:42 AM
Room: The Moscone Center: 250-262

Background: FDA-approved 4th-generation HIV antigen/antibody immunoassays can detect HIV infection earlier than traditional confirmatory tests (i.e., Western blot). Screening and confirmatory test results (4th-generation reactive / Western blot negative) that are discordant may be misclassified as HIV-negative by clinicians. Use of an algorithm with HIV-1 Nucleic Acid Amplification Testing (NAAT) for confirmation enables proper classification of reactive 4th-generation test results. We report a prospective evaluation of a testing algorithm using HIV-1 NAAT to confirm reactive 4th-generation results.

Methods: The STOP study is an ongoing, multi-site study comparing methods to detect acute HIV infection. In New York City, participants at three STD clinics and two community-based testing programs were screened for HIV with a 4th-generation antigen/antibody immunoassay (Architect, Abbott). Specimens with a reactive 4th-generation result were tested with a qualitative HIV-1 NAAT (APTIMA, Gen-Probe), Western blot (WB, Bio-Rad), and a HIV-1/HIV-2 antibody differentiation assay (Multispot, Bio-Rad).

Results: From October 3, 2011 to March 11, 2013, we tested 13,931 specimens with the 4th-generation assay, of which 501 (3.6%) were reactive. HIV-1 RNA was detected in 459 (92%) of these specimens by HIV-1 NAAT (Figure 1). Among the 42 specimens with HIV-1 RNA not detected by NAAT, 7 (1.4%) were reactive by both WB and Multispot, consistent with HIV-1 infection. Three of these 7 individuals were determined to have newly diagnosed HIV infection and denied any HIV antiretroviral use, 4 were already aware of their HIV status. Overall, among 466 HIV infections that were diagnosed in this study, HIV-1 infection was confirmed by NAAT in 98.5% of cases (n=459) compared with 93.6% confirmed by Multispot (n=437; p<0.0001) and 95.1% by WB (n=443; p<0.0001), respectively.  

Conclusion: In an HIV testing algorithm that uses a 4th-generation assay as the screening test, NAAT confirmed a higher proportion of HIV infections than Multispot or WB. Discordant 4th-generation/NAAT results (4th-generation reactive/NAAT not detected), however, must be resolved by Multispot or WB to properly diagnose infections in persons with undetectable levels of HIV RNA.


Emily Westheimer, MSc, Bureau of STD Prevention and Control, New York City Department of Health and Mental Hygiene, Queens, NY, Philip Peters, MD, Centers for Disease Control and Prevention, Atlanta, GA, Jie Fu, PhD, Bureau of Public Health Labs, New York City Department of Health and Mental Hygiene, New York, NY, Francesca R. Giancotti, PhD, Bureau Of Public Health Labs, New York City Department of Health and Mental Hygiene, New York, NY, Anita Radix, MD, MPH, Callen-Lorde Community Health Center, New York, NY, Demetre Daskalakis, MD, New York University School of Medicine, New York, NY and Benjamin Tsoi, MD, MPH, Bureau of HIV/AIDS Prevention, New York City Department of Health and Mental Hygiene, Queens, NY


E. Westheimer, None

P. Peters, None

J. Fu, None

F. R. Giancotti, None

A. Radix, None

D. Daskalakis, None

B. Tsoi, None

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