Urban Schmitt

Multicenter Evaluation of a New Automated Fourth-Generation Human Immunodeficiency Virus Screening Assay with a Sensitive Antigen Detection Module and High Specificity

ABSTRACT Fourth-generation assays for the simultaneous detection of human immunodeficiency virus (HIV) antigen and antibody that were available on the international market until now have antigen detection modules with relatively poor sensitivity and produce a higher rate of false-positive results than third-generation enzyme immunoassays (EIAs). The new Cobas Core HIV Combi EIA with an improved sensitivity for HIV p24 antigen was compared to alternative fourth- and third-generation assays, the p24 antigen test, and HIV type 1 (HIV-1) RNA reverse transcriptase PCR (RT-PCR). A total of 94 seroconversion panels (n = 709 sera), samples from the acute phase of infection after seroconversion (n = 32), anti-HIV-1-positive specimens (n = 730) from patients in different stages of the disease, 462 subtyped samples from different geographical locations, anti-HIV-2-positive sera (n = 302), dilutions of cell culture supernatants (n = 62) from cells infected with different HIV-1 subtypes, selected performance panels from Boston Biomedica Inc., 7,579 unselected samples from blood donors, 303 unselected daily routine samples, 997 specimens from hospitalized patients, and potentially interfering samples (n = 1,222) were tested with Cobas Core HIV Combi EIA. The new assay showed a sensitivity comparable to that of the Abbott HIV-1 AG Monoclonal A for early detection of HIV infection in seroconversion panels. The mean time delay of Cobas Core HIV Combi EIA (last negative sample plus 1 day) in comparison to that for HIV-1 RT-PCR for 87 panels tested with both methods was 2.75 days. The diagnostic window was reduced with Cobas Core HIV Combi EIA by between 3.6 and 5.7 days from that for third-generation assays. The specificities of Cobas Core HIV Combi EIA in blood donors were 99.84 and 99.85% (after repeated testing). Overall, 30 repeatedly reactive false-positive results out of 10,031 HIV-negative samples were obtained with Cobas Core HIV Combi EIA. Our results show that a fourth-generation assay with improved specificity such as Cobas Core HIV Combi EIA is suitable for blood donor screening because of its low number of false positives and because it detects HIV p24 antigen with a sensitivity comparable to that of single-antigen assays.

Distinct prevalence of antibodies to the E2 protein of GB virus C/hepatitis G virus in different parts of the world.

Since the identification of the new human virus, GB virus C (GBV‐C)/hepatitis G virus (HGV), in 1995/1996, reverse transcription polymerase chain reaction remained the sole available diagnostic tool for GBV‐C/HGV infection. Recently, a serologic test based on the detection of antibodies to the putative envelope protein 2 (anti‐E2) has been introduced. We used this assay for a seroepidemiological survey including 3,314 healthy individuals from different parts of the world, 123 patients from Germany who were suspected to have an increased risk of acquiring GBV‐C/HGV infection, 128 multiple organ donors, and 90 GBV‐C/HGV RNA positive persons. In European countries, anti‐E2 seropositivity ranged from 10.9% (Germany) to 15.3% (Austria). In South Africa (20.3%) and Brazil (19.5%), even higher anti‐E2 prevalence rates were recorded. In Asian countries like Bhutan (3.9%), Malaysia (6.3%), and the Philippines (2.7%), anti‐E2 positivity was significantly lower. GBV‐C/HGV anti‐E2 prevalence in potential “risk groups,” i.e., patients on hemodialysis and renal transplant recipients, did not vary significantly from anti‐E2 seroprevalence in German blood donors. Anti‐E2 and GBV‐C/HGV RNA were found to be mutually exclusive, confirming the notion that anti‐E2 has to be considered as a marker of past infection. J. Med. Virol. 54:103–106, 1998.

Multicenter evaluation of a new rapid automated human immunodeficiency virus antigen detection assay.

Although human immunodeficiency virus (HIV) antigen assays are of limited value for monitoring antiretroviral therapy, they play an important role for confirmatory testing of fourth generation HIV screening enzyme immunoassay (EIA) reactive samples. In a multicenter study, a new automated rapid p24 antigen assay, Elecsys HIV Ag (Roche Diagnostics Boehringer Mannheim GmbH, Penzberg, Germany), was compared to FDA licensed tests (Abbott HIV-1 Ag monoclonal and Coulter HIV-1 p24 antigen assay). In the evaluation 27 seroconversion panels were included, sera from the acute phase of infection, single and follow-up samples from HIV antibody positive patients, dilution series of HIV antigen positive standards, sera and cell culture supernatants infected with different HIV-1 subtypes (A-H, and O) HIV-2 and recombinant HIV-1 (gag/env) isolates. To challenge the specificity of the new assay, 2565 unselected blood donors, sera from pregnant women, dialysis and hospitalized patients and 407 potentially cross-reactive samples were investigated. Acute HIV infection was detected in three to eight seroconversion panels earlier with Elecsys HIV Ag than with the alternative assays. Higher numbers of serum samples from HIV infected patients tested positive by Elecsys HIV Ag than with the comparative assays. All HIV-1 subtypes and HIV-2 isolates were recognized with Elecsys HIV Ag. Abbott HIV-1 Ag monoclonal and Coulter HIV-1 p24 antigen assay showed a variable sensitivity for the different HIV-1 subtypes. The specificity of Elecsys HIV Ag and Coulter HIV-1 p24 antigen assay were 99.8 and 99.93%, respectively. All the eight sera that were false reactive by Elecsys HIV Ag were tested negative with the Elecsys HIV Ag Neutralization Test. In conclusion, Elecsys HIV Ag was more sensitive than the alternative assays and showed a high specificity in combination with the neutralization assay. The very short incubation time of 18 min and the fully automated procedure of Elecsys HIV Ag which permits direct testing from the primary patient blood collection tube, represent a major improvement for routine laboratory diagnosis in comparison to the alternative assays.

Antibodies to the E2 protein of GB Virus C/hepatitis G virus: low prevalence in Asian countries

Epidemiological investigations of GB virus C (GBV-C)/hepatitis G virus (HGV), an infectious agent discovered in 1995/1996, are facilitated by a recently developed immunoassay for the detection of antibodies to the viral envelope 2 protein (anti-E2). We used this assay to establish GBV-C/HGV prevalence in seven European, African, and Asian countries. A total of 1579 serum samples from healthy adults lacking prior exposure to known parenteral risk factors was screened. Anti-E2 positivity ranged from 13.6% (Italy) to 7.7% (Mauritius) in the European and African countries investigated. Anti-E2 prevalence was exceedingly low in the Philippines and Sri Lanka. This observation might be attributable to socio-economical and demographic factors.