Background: CDC recently released new guidelines for laboratory diagnosis of HIV infection in the United States (the “CDC algorithm”), which recommends use of an assay that differentiates HIV-1 from HIV-2 after a reactive HIV-1/HIV-2 screening test. Currently only the Multispot HIV-1/HIV-2 differentiation test (MS) is FDA-approved for this use. A new test, the Geenius HIV-1/HIV-2 Supplemental assay (Geenius), has been proposed to replace MS.
Methods: We evaluated Geenius with a panel of specimens previously tested with FDA-approved screening tests, MS and the Aptima RNA assay (NAT) and classified by the CDC algorithm. The 873 specimens included 658 classified as HIV-1 by the CDC algorithm (HIV1+), 8 classified as acute HIV-1 infections (acute), and 207 specimens with reactive results on at least one HIV-1/HIV-2 screening test identified from 4500 previously collected specimens classified as negative (HIV-): 176 with a reactive HIV screening test result other than MS, 5 reactive on another screening test and MS, and 26 with only a reactive MS screening test result. We compared Geenius results with those from the CDC algorithm and MS.
Results: Of 658 HIV1+ specimens, Geenius classified 654 (99.4%) as HIV1+, 1 as HIV-, 1 as HIV-1 indeterminate (HIV-1 IND), and 2 as HIV-positive “untypeable.” (Both these specimens were initially positive for both HIV-1 and HIV-2 with MS, but classified as HIV-1 after dilution). Thirteen additional HIV1+ specimens that were positive for both HIV-1 and HIV-2 by MS before dilution were positive for HIV-1 only by Geenius. One of 8 acute HIV specimens was HIV-2 IND by Geenius and HIV- by MS; all others were HIV- with both tests. Of the 181 HIV- specimens with a reactive non-MS screening test result, 165 (91.2%) were classified as HIV- by Geenius; one of the remaining 16 was classified as HIV1+. Of 31 HIV- specimens with a reactive MS screening result, 24 were classified as HIV- by Geenius; none were concordantly reactive with MS and HIV-1 positive by Geenius. The majority of the non-negative Geenius results were HIV-2 IND (Table). All HIV- specimens categorized as HIV-2 IND were attributable to reactivity at the gp140 HIV-2 peptide line only.
Conclusions: The ability of the Geenius to detect established and early HIV infection is similar to the MS currently used in the CDC algorithm, but more IND results, particularly HIV-2 IND results, occur with Geenius.
|Geenius HIV-1/HIV-2 differentiation assay interpretation||Total|
|HIV Negative||HIV Indeterminate||HIV-2 Indeterminate||HIV-1 Indeterminate||HIV Positive, “Untypeable”||HIV-2 Positive||HIV-1 Positive|
|Multispot supplemental test interpretation**||HIV-1 Only
|HIV-1 Indeterminate (only 1 of 2 spots)||3||3|
|Multispot screening test interpretation***||Reactive||24||2||4||1||0||0||0||31|
*207 specimens with false-reactive results on one or more HIV screening tests were obtained from a previous study of 4500 HIV-negative specimens. ** Multispot supplemental test interpretation: reactivity at both HIV-1 spots required for positive; reactivity at only one of two HIV-1 spots is considered indeterminate; reactivity at both HIV-1 and HIV-2 spots is considered HIV-1/HIV-2 undifferentiated. ***Multispot screening test interpretation: any reactivity at any spot is considered reactive; the 31 include 5 with reactivity to another HIV-1/HIV-2 screening assay