Objective: We evaluated the performance of the GS fourth-generation antigen/antibody assay and compared Centers for Disease Control and Prevention's (CDC's) proposed alternative algorithm [repeatedly reactive fourth-generation immunoassay followed by an HIV-1/HIV-2 differentiation immunoassay and, if needed, nucleic acid test (NAT)] with the current algorithm (repeatedly reactive third-generation immunoassay followed by HIV-1 western blot).
Design: A convenience sample of the following four specimen sets was acquired: 10 014 from insurance applicants, 493 known western blot-positive, 20 known western blot-indeterminate specimens, and 230 specimens from 26 HIV-1 seroconverters.
Methods: Specimens were tested with the GS third-generation and fourth-generation immunoassays, the Multispot HIV-1/HIV-2 differentiation immunoassay, NAT, and western blot. We applied the two algorithms using these results.
Results: Among insurance specimens, 13 (0.13%) specimens were immunoassay repeatedly reactive: two were HIV-positive (repeatedly reactive by third-generation and fourth-generation immunoassays, and western blot and Multispot positive); two third-generation repeatedly reactive and nine fourth-generation repeatedly reactive specimens were false-positive. Third-generation and fourth-generation specificities were 99.98% [95% confidence interval (CI) 99.93–100%] and 99.91% (95% CI 99.84–99.96%), respectively.
All HIV-1 western blot-positive specimens were repeatedly reactive by third-generation and fourth-generation immunoassays. By Multispot, 491 (99.6%) were HIV-1-positive and two (0.4%) were HIV-2-positive.
Only eight (40%) western blot-indeterminate specimens were fourth-generation repeatedly reactive: six were Multispot and NAT-negative and two were Multispot HIV-1-positive but NAT-negative.
The alternative algorithm correctly classified as positive 102 seroconverter specimens with the third-generation immunoassay and 130 with the fourth-generation immunoassay compared with 56 using the western blot with either immunoassay.
Conclusion: The alternative testing algorithm improved early infection sensitivity and identified HIV-2 infections. Two potential false-positive algorithm results occurred with western blot-indeterminate specimens.
aDivision of HIV/AIDS Prevention, National Center for HIV, Hepatitis, STD and TB Prevention, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia
bQuest Diagnostics, Baltimore, Maryland
cQuest Diagnostics, Collegeville, Pennsylvania
dQuest Diagnostics, Lenexa, Kansas, USA.
Correspondence to Muazzam Nasrullah, MD, MPH, Division of HIV/AIDS Prevention, National Center for HIV, Hepatitis, STD and TB Prevention, Centers for Disease Control and Prevention, 1600 Clifton Rd, Mailstop E46, Atlanta, GA 30333, USA. Tel: +1 404 639 3271; fax: +1 404 639 8640; e-mail: firstname.lastname@example.org
Received 29 August, 2012
Revised 17 October, 2012
Accepted 22 October, 2012