Performance of the new HIV-1/2 Diagnostic Algorithm in Florida's public health testing population: A review of the first five months of utilization

Abstract

ObjectiveThe Centers for Disease Control and Prevention and the Association of Public Health Laboratories have proposed a new HIV-1/2 Diagnostic Algorithm: a fourth-generation HIV-1/2 Ag/Ab immunoassay (IA) followed, when repeatedly reactive, by an HIV-1/HIV-2 antibody differentiation test, and if that is non-reactive, HIV-1 nucleic acid amplification testing (NAT). The objective of the study was to evaluate performance of the new algorithm after five months of utilization in our high volume, high HIV-1 seroprevalence public health population. MethodsAlgorithm sensitivity and specificity was evaluated on 51,953 prospective serum or plasma specimens from individuals self-referring for HIV serostatus determination. Specimens were tested on the day of receipt or maintained at 4°C until the next testing opportunity. If the initial HIV-1/2 Ag/Ab IA (Abbott Combo) was nonreactive, a negative lab interpretation report would follow. If the initial IA was reactive, repeat screening in duplicate was immediately performed. Repeatedly reactive specimens were tested with an HIV-1/HIV-2 differentiation assay (Multispot [MS] HIV-1/HIV-2 Rapid Test) on the same or next workday. If the Abbott Combo-MS assays were discordant, HIV-1 NAT (APTIMA® HIV-1 RNA) was performed. In addition to the algorithm performance, we also evaluated the laboratory “specimen receipt to reporting” turnaround time (TAT). ResultsThe sensitivity and specificity of the new HIV Diagnostic Algorithm with serum and plasma specimens over the initial 5 month period was 100% (922/922) and 99.99% (51,030/51,031), respectively. Two algorithm-defined acute HIV-1 infections (AHI) were detected. In addition only 3 of the 992 MS secondary tests performed were interpreted as HIV-1 Indeterminate (HIV-1 recombinant gp41 reactivity only). Of these, 2 were HIV-1 NAT reactive, defined in-house as an early HIV infection (EHI) and one was HIV-1 NAT nonreactive, indicating a false positive initial screening result. Laboratory TAT for reporting concordant reactive Abbott Combo-MS results in ≤2 workdays was 96%, compared to 22% for reporting concordant reactive 3rd generation IA-Western blot results. ConclusionsIn our public health testing population, results from the new HIV Diagnostic Algorithm exceeded those of the 3rd generation IA-WB algorithm with respect to HIV-1 sensitivity. The identification of two algorithm-defined AHIs provided the opportunity to inform these individuals of their HIV status and link them to medical care earlier than the scheduled posttest counseling appointment.