Ultrasensitive human immunodeficiency virus type 1 p24 antigen assay modified for use on dried whole-blood spots as a reliable, affordable test for infant diagnosis

The ultrasensitive human immunodeficiency virus (HIV) p24 antigen assay was modified for use on pediatric dried whole-blood spots on Whatman no. 1 filter paper. The modified assay was found to be reliable and accurate, making it an affordable tool for pediatric HIV diagnosis in developing countries.

Evaluation of HIV-1 p24 Antigenemia and Level of CD8+CD38+ T cells as Surrogate Markers of HIV-1 RNA Viral Load in HIV-1-Infected Patients in Dakar, Senegal

Alternative, affordable, and simple assays to monitor antiretroviral therapy (ART) in resource-poor settings are needed. We have evaluated and compared a heat-denatured (HD) HIV p24 amplified enzyme-linked immunosorbent assay from Perkin-Elmer and CD38CD8 T-cell levels, determined by flow cytometry, for their capacity to predict viral load (VL) in HIV-1-infected patients from Senegal. Median fluorescence intensity (MFI) of CD38 expression on memory (CD45RO) CD8 T cells correlated better with RNA VL than HD p24 antigenemia (R = 0.576, P < 0.0001 vs R = 0.548, P < 0.0001). MFI of CD38 expression on memory CD8 T cells could predict detectable RNA VL (VL = 2.6 log10) with a sensitivity of 87% and a specificity of 74%. A comparable sensitivity (89%) could be reached for HD p24 assay, but only to predict RNA VL of more than 5 logs, which might lead to unacceptable delays in clinical decision making. The clinical use of the HD p24 assay to monitor ART in Senegal would require more comparative data about the kinetics of p24 antigen and HIV RNA in peripheral blood as well as further evaluation regarding its sensitivity toward subtype A and CRF02. MFI of CD38 expression on memory CD8 T cells appeared to be a better alternative to monitor ART in HIV-infected patients from Senegal.

Comparison of two human immunodeficiency virus (HIV) RNA surrogate assays to the standard HIV RNA assay

Human immunodeficiency virus (HIV) RNA testing is the gold standard for monitoring antiretroviral therapy in HIV-infected patients. However, equipment and reagent costs preclude widespread use of the assay in resource-limited settings. The Perkin-Elmer Ultrasensitive p24 assay and the Cavidi Exavir Load assay both offer potentially simpler, less costly technologies for monitoring viral load. These assays were compared to the Roche Amplicor HIV-1 Monitor Test, v1.5, using panels of clinical samples (subtype B) from HIV-positive subjects and HIV-spiked samples (subtypes A, C, D, CRF_01AE, CRF_02AG, and F). The Ultrasensitive p24 assay detected 100% of the spiked samples with virus loads of >250,000 copies/ml and 61% of the clinical samples with virus loads of 219 to 288,850 copies/ml. Detection rates were improved substantially if an external lysis buffer was added to the procedure. The Cavidi assay detected 54 to 100% of spiked samples with virus loads >10,000 copies/ml and 68% of the clinical samples. These detection rates were also greatly improved with a newly implemented version of this kit. Coefficients of variation demonstrate good reproducibility for each of these kits. The results from the Cavidi v1.0, Cavidi v2.0, and Perkin-Elmer, and the Perkin-Elmer Plus external buffers all correlated well with the results from the Roche Monitor Test (r = 0.83 to 0.96, r = 0.84 to 0.99, r = 0.58 to 0.67, and r = 0.59 to 0.95, respectively). Thus, the use of these two assays for monitoring patients, together with less-frequent confirmation testing, offers a feasible alternative to frequent HIV RNA testing in resource-limited settings.

Multicenter evaluation of a new 4th generation HIV screening assay Elecsys HIV combi

Fourth-generation screening assays which permit a simultaneous detection of human immunodeficiency virus (HIV) antigen and antibody reduce the diagnostic window on average by four days in comparison to third-generation antibody assays. Recently, the new automated Elecsys HIV combi was compared in a multicenter study to alternative fourth- and third-generation assays, p24 antigen test and HIV-1 RNA RT-PCR. A total of 104 serocon-version panels, samples of the acute phase of infection after seroconversion (n = 33), anti-HIV-1 positive specimens (n = 572) from patients in different stages of the disease, 535 subtyped samples from different geographical locations, including group M (subtypes A-J) and group O, anti-HIV-2 positive sera (n = 364), dilutions of cell culture supernatants (n = 60) infected with different HIV-1 subtypes, selected performance panels, 8406 unselected samples from blood donors originating from different blood transfusion centers, 3810 unselected sera from daily routine and from hospitalized patients, 9927 unselected samples from South Africa and 1943 potentially interfering samples were tested with the Elecsys HIV combi. Elecsys HIV combi showed a comparable sensitivity to HIV-1 Ag stand-alone assays for early detection of HIV infection in seroconversion panels. The mean time delay of Elecsys HIV combi (last negative sample + 1 day) in comparison to HIV-1 RT-PCR for 92 panels tested with both methods was 3.23 days. The diagnostic window was reduced with Elecsys HIV combi between 1.56 and 5.32 days in comparison to third-generation assays. The specificity of Elecsys HIV combi in blood donors was 99.80% after repeated testing. Our results show that a fourth-generation assay with improved specificity and sensitivity like the Elecsys HIV combi is suitable for blood donor screening due to its low number of false positives and since it detects HIV p24 antigen with a comparable sensitivity to single antigen assays.

HIV-1 p24 may persist during long-term highly active antiretroviral therapy, increases little during short treatment breaks, and its rebound after treatment stop correlates with CD4(+) T cell loss

The dynamics of HIV-1 RNA during structured treatment interruptions (STIs) are well established, but little is known about viral proteins like p24. We studied 65 participants of an STI trial. Before the trial, continuous highly active antiretroviral therapy (HAART) had suppressed their viral load to <50 copies/mL during 6 months. They then interrupted HAART during weeks 1 through 2, 11 through 12, 21 through 22, 31 through 32, and 41 through 52. The p24 was measured by boosted enzyme-linked immunosorbent assay of plasma pretreated by efficient virus disruption and heat denaturation. At time point 0, p24 was measurable in 22 patients (34%), who had maintained a viral load <50 copies/mL for 25.4 months (median, range: 6.2-38.9 months) under HAART. Viral rebounds during 2-week STIs led to a mean p24 increase of only 0.08 to 0.19 log10 (ie, 20%-60%). Pre-HAART viral load and p24 at time 0 independently predicted p24 rebounds during the 4 2-week STIs. The p24 at time 0 and HIV-1 RNA rebound during weeks 41 through 52 independently determined the concomitant p24 rebound. An increase of p24 but not viral load during the first 8 weeks of the long STI correlated significantly with concomitant CD4(+) T cell loss. Persisting p24 despite successful HAART may reflect virus replication in reservoirs not represented by plasma viral load and has implications for the concept of therapeutic vaccination.

Comparative evaluation of TRI-DOT Rapid HIV test with fourth-generation ELISA for the detection of human immunodeficiency virus

This study evaluated the TRI-DOT Rapid HIV test for the early detection of human immunodeficiency virus (HIV) infection in comparison with a fourth-generation ELISA (Vironostika HIV Uniform II). Of 23,609 sera, seven (0.03%) gave discordant results. Six of these were reactive only by the fourth-generation assay and were p24 antigen-positive by VIDAS DUO, Western blot and qualitative RT-PCR tests. The remaining discordant serum was considered to be false-positive by the TRI-DOT assay, as it was negative by repeat ELISA and Western blot tests. The sensitivity and specificity of the TRI-DOT test were 99.48% and 99.99%, respectively, compared with the fourth-generation ELISA.

Combination assay detecting both human immunodeficiency virus (HIV) p24 antigen and anti-HIV antibodies opens a second diagnostic window

Fourth-generation human immunodeficiency virus (HIV) screening immunoassays reduce the diagnostic window between infection and diagnosis by the inclusion of HIV p24 antigen detection together with HIV antibody detection in the same test. We compared third- and fourth-generation HIV immunoassays and a dedicated HIV p24 antigen test for detection of a case of HIV seroconversion. This demonstrated a second diagnostic window using the fourth-generation assay due to a decline of HIV p24 antigen prior to the detection of HIV antibody. However, HIV p24 antigen was detected in the same sample by the dedicated HIV p24 antigen test, as was HIV proviral DNA. Although it is likely to be rare, this phenomenon has also been reported for other fourth-generation HIV immunoassays and has implications for the reported diagnostic windows of these assays.

Performance evaluation of three automated human immunodeficiency virus antigen-antibody combination immunoassays

Three fourth-generation antigen/antibody combination assays (Elecsys, AxSYM, Architect HIV) and two third-generation (AxSYM, Centaur) HIV antibody immunoassays were evaluated. The evaluation panel of 479 samples included: nine tissue culture derived HIV-1 strains at four different p24 antigen concentrations (n=36), a p24 antigen sensitivity panel (n=10), 149 HIV-1 or HIV-2 confirmed antibody positive samples, ten anti-HIV-1 positive low titer samples, three seroconversion panels (n=21), and 253 HIV negative samples. The Architect had the best sensitivity for detection of HIV-1 antigen across eight HIV-1 subtypes, followed by the AxSYM while the Elecsys could not detect the highest antigen concentration evaluated (25 pg/mL) for eight of nine virus isolates. All assays showed 100% sensitivity for detection of HIV-1, group M, group O, and HIV-2 antibody positive samples. The Architect Ag/Ab Combo assay detected the first positive bleed of the three seroconversion panels and detected infection 4-26 days earlier than the third generation assays. Based on evaluation of 253 negative samples, assay specificity varied from 98.0% to 99.6%. The Architect HIV Ag/Ab Combo exhibited the best performance for specificity and detection of p24 antigen leading to closure of seroconversion window and demonstrating its utility for early diagnosis of HIV infection.

Natural controlled HIV infection: preserved HIV-specific immunity despite undetectable replication competent virus

Long-term non-progressive HIV infection, characterized by low but detectable viral load and stable CD4 counts in the absence of antiviral therapy, is observed in about 5% of HIV-infected patients. Here we identified four therapy naïve individuals who are strongly seropositive for HIV-1 but who lack evidence of detectable HIV p24 antigen, plasma RNA, and proviral DNA in routine diagnostic testing. With an ultrasensitive PCR, we established that frequencies of pol proviral DNA sequences were as low as 0.2-0.5 copies/10(6) PBMC. HIV could not be isolated using up to 30x10(6) patient PBMC. One individual was heterozygous for CCR5 Delta32, but CCR5 expression on CD4+ T cells was normal to high in all four individuals. In vitro R5 and X4 HIV-1 susceptibility of CD8-depleted PBMC of all study subjects was significantly lower than the susceptibility of CD8-depleted PBMC of healthy blood donors. All individuals expressed protective HLA-B*58s alleles and showed evidence of HIV-specific cellular immunity either by staining with HLA-B*57 tetramers folded with an HIV RT or gag peptide or after stimulation with HIV-1 p24 gag, RT, or nef peptides in ELIspot analysis. HIV-specific CD4+ T helper cells were demonstrated by proliferation of CD4+ T cells and intracellular staining for IL-2 and IFNgamma after stimulation with an HIV-gag peptide pool. Sera of all individuals showed antibody-mediated neutralization of both R5 and X4 HIV-1 variants. These data implicate that very low-level antigen exposure is sufficient for sustained HIV-specific immunity and suggest the possibility of a multi-factorial control of HIV infection.

Comparative evaluation of the VIDAS HIV DUO Ultra assay for combined detection of HIV-1 antigen and antibodies to HIV

The aim of the study was to evaluate the performance of the combined antigen and antibody HIV screening assay VIDAS HIV DUO Ultra (BioMérieux, Marcy l'Etoile, France) in comparison with two other combined tests: the former version of the same test (VIDAS HIV DUO, BioMérieux) and the AxSYM HIV Ag/Ab Combo assay (Abbott Laboratories, Rungis, France). A prospective study was performed on serum specimens received on a routine basis for HIV testing: 1443 blood samples were tested with the three assays. Sensitivity was 100% for the three tests. Specificity assessed on repeated false-positive samples was 99.86, 99.03 and 99.65% for VIDAS HIV DUO Ultra, VIDAS HIV DUO and AxSYM HIV Ag/Ab Combo, respectively. In addition, 14 seroconversion panels were tested with the VIDAS DUO Ultra and AxSYM HIV Ag/Ab Combo assays. For four of these panels, a positive signal was detected one blood sampling point earlier with the VIDAS DUO Ultra assay, corresponding to a higher sensitivity of the HIV antigen test. These results indicate that the VIDAS HIV DUO Ultra exhibits an improved specificity with comparison to the former version of this assay and an excellent sensitivity for early detection of HIV seroconversion.

Detection and quantification of human immunodeficiency virus type 1 p24 antigen in dried whole blood and plasma on filter paper stored under various conditions

The quantification of human immunodeficiency virus type 1 (HIV-1) by an assay measuring heat-dissociated (HD) p24 antigen (Ag) in specimens of whole blood and plasma stored on filter paper, and of plasma stored in tubes, was compared to HIV-1 RNA plasma levels determined by real-time reverse transcription (RT)-PCR. The stability of p24 Ag on filter paper under conditions simulating specimen transport was also evaluated. The HD p24 Ag in both plasma and whole-blood specimens stored on filter paper correlated with plasma HIV-1 RNA levels (Spearman rank rho = 0.74 [P < 0.0001] and rho = 0.56 [P = 0.0001], respectively). The sensitivity of the HD p24 Ag assay was similar when plasma and whole blood on filter paper were contrasted to the real-time RT-PCR assay (80% versus 82.5% and 78.6% versus 83.3%, respectively). However, while the specificity of the HD p24 Ag assay of plasma on filter paper was 100%, the specificity was diminished in whole-blood specimens. The storage of specimens on filter paper for 2 weeks at 37 degrees C, 24 degrees C, or 0 degrees C did not alter the detection or quantification of HD p24 Ag. These results suggest that transport and storage of plasma on filter paper and quantification of HD p24 Ag may be a reliable method for HIV-1 load monitoring.

Signal-boosted qualitative ultrasensitive p24 antigen assay for diagnosis of subtype C HIV-1 infection in infants under the age of 2 years

The gold standard for diagnosis of HIV-1 infection in infants under the age of 2 years is DNA or reverse transcriptase polymerase chain reaction. However, these tests are expensive and therefore not available in resource-limited countries. With the increasing availability of antiretroviral drugs for prevention of mother-to-child transmission of HIV and treatment of AIDS in resource-poor countries, there is an urgent need to develop cheaper, alternative, and cost-effective laboratory methods for early diagnosis of infant HIV-1 infection that will be useful in identifying infected infants who may benefit from early cotrimoxazole prophylaxis or commencement of antiretroviral therapy. We evaluated an alternative method, the enzyme-linked immunosorbent assay-based qualitative ultrasensitive p24 antigen assay for diagnosis of subtype C HIV-1 infection in infants under the age of 2 years using DNA polymerase chain reaction as the reference method. The assay showed a sensitivity of 96.7% (95% CI: 93.0-100) for detection of HIV-1 infection among infants 0-18 months of age with a specificity of 96.1% (95% CI: 91.7-100). These evaluated parameters were not statistically different between infants aged 0-6 and 7-18 months. The ultrasensitive p24 antigen assay is a useful diagnostic test for detection of HIV-1 infection among infants aged 0-18 months.

Alternatives to HIV-RNA and CD4 count to monitor HIV disease progression: a prospective cohort study in Romania

Little evidence exists on how to efficiently and effectively monitor HIV-disease progression in developing countries. Better understanding regarding cost-effective tests may help to resolve questions regarding treatment. A prospective cohort study was conducted with a 1-year follow-up period. Immune complex-dissociated (ICD) p24 antigen (ICD p24Ag), alone or in combination with HIV p24 antibody (p24Ab), was compared to HIV-RNA and CD4+ count in a cohort of 160 HIV-infected adolescents in Romania. The main outcome measure was disease progression, defined as >50,000 copies/ml of HIV-RNA or death. Among the 160 adolescents, a higher mean ICD p24Ag was significantly associated with clinical disease classification (CDC), plasma HIV-RNA concentration, and p24Ab. Multivariate logistic regression showed detectable ICD p24Ag had an odds ratio of 3.7 (95% CI 1.4-9.7) for disease progression in comparison to undetectable ICD p24Ag. ICD p24Ag is of value in determining the prognosis of disease in HIV-1-infected adolescents in developing countries. Additional studies for validation of this assay for HIV clades primarily affecting developing countries, are now needed.

Evaluation of two commercially available, inexpensive alternative assays used for assessing viral load in a cohort of human immunodeficiency virus type 1 subtype C-infected patients from South Africa

Although human immunodeficiency virus type 1 (HIV-1) RNA is the acknowledged "gold standard" marker for monitoring disease activity in patients receiving highly active antiretroviral therapy (HAART), it remains unaffordable in resource-constrained settings. The present study investigated two commercially available kits for the detection of HIV-1 viral load markers as more affordable alternatives to HIV-1 RNA quantitation. The greatly improved heat-denatured, signal-boosted HiSens HIV-1 p24 Ag Ultra kit (Perkin-Elmer) and the ExaVir Load Quantitative HIV-RT kit (Cavidi Tech AB) were compared with the Amplicor HIV-1 Monitor (version 1.5) assay (Roche Molecular Systems Inc.). A total of 117 samples containing HIV-1 subtype C were analyzed by all three methodologies. Eighty-nine of these samples represented serial measurements from 20 patients receiving HAART. The remaining samples analyzed were from a group of treatment-naive patients. The association between the p24 antigen assay and the RNA assay was fairly strong (R(2) = 0.686). The association between the reverse transcriptase (RT) quantitation assay and the RNA assay was strong (R(2) = 0.810). Both alternative assays seemed most useful for the serial monitoring of patients receiving HAART (n = 89 plasma samples from 20 patients), as all assays showed a statistically significant downward trend over time, with the trend being either linear or curvilinear. In addition, all three assays showed negative correlations with the CD4 count (CD4 count versus RNA load, r = -0.336 and P = 0.001; CD4 count versus p24 antigen level, r = -0.541 and P < 0.0001; CD4 count versus RT level, r = -0.358 and P = 0.0006). Still of major concern are both the lack of sensitivity and the wide degrees of variability of both assays. However, both assays provide a less expensive alternative to the Roche viral load assay and demonstrate the same trends during treatment.

Evaluation of an ultrasensitive p24 antigen assay as a potential alternative to human immunodeficiency virus type 1 RNA viral load assay in resource-limited settings

An inexpensive enzyme-linked immunosorbent assay method for human immunodeficiency virus type 1 quantitation, ultrasensitive p24 antigen assay (Up24), was compared with RNA viral load assay (VL). Up24 had 100% sensitivity of detection at a viral load of >/=30,000, with sensitivity of 46.4% at a viral load of <30,000 (232 specimens from 65 seropositive subjects). The assay was highly reproducible, with excellent correlation between duplicates and among three laboratories.

Evaluation of the sensitivity and specificity of six HIV combined p24 antigen and antibody assays

In this study, we evaluated the performance of six HIV combined p24 antigen and antibody (Ag/Ab) assays versus two third-generation anti-HIV antibody assays. The assays were evaluated using p24 antigen panel of 31 HIV-1 subtypes (n = 124), 25 HIV-1 seroconversion panels (n = 176), HIV-1 antibody positive samples including group M subtypes and group O (n = 559), HIV-2 positive samples (n = 110), and unselected HIV negative samples from four French private laboratories (n = 1005). The results showed that overall HIV combined Ag/Ab assays present better performance, when compared to antibody-only assays. However, some differences were observed in the sensitivity of the six HIV combined Ag/Ab assays evaluated. The AxSYM and Murex Combo assays had the best sensitivity score in this study and reduced the window period by 2.0-2.35 days relative to antibody only assays and 1-2.17 days relative to the other combined Ag/Ab assays. Among combined HIV Ag/Ab assays, Genscreen Plus and AxSYM Combo presented the highest specificity, with 99.9% and 99.8%, respectively.

Laboratory markers associated with progression of HIV infection

Infection with HIV may develop to AIDS at different rates in different individuals, with a spectrum varying from rapid progression to long-term non-progression. The variable course of HIV-1 infection causes emotional trauma for the infected person and complicates the design and interpretation of therapeutic trials because of unrecognized differences in prognosis. Owing to the variable clinical expression of HIV infection, the use of non-clinical disease markers has become important to patient management. Thus, it is essential to have tests which can accurately assess the stage of infection in an individual, as well as predict its course and monitor its progression. These laboratory tests are valuable during the period of clinical latency and subsequently supplement various clinical parameters.

A new combined HIV p24 antigen and anti-HIV-1/2/O screening assay

It is important to shorten the window period after acute HIV infection in which infected individuals are still antibody-negative, especially in blood donors. Newly developed fourth-generation assays detect antibodies to HIV-1, including subtype O, and to HIV-2 and, simultaneously, p24 antigen of HIV-1. To evaluate this assay for daily routine work we compared it with different third-generation assays using sera from uninfected patients and patients with known HIV infection. The most interesting sera are those drawn during seroconversion from freshly infected patients. Whenever we encounter such a patient with acute HIV infection we store the serum in aliquots at -20 degrees C. Thus, we were able to establish our own seroconversion panel and use it in our laboratory for evaluation of new assays. The new test was shown to be able to detect all chronically HIV-infected individuals and four of six patients during seroconversion although in two of these patients conventional assays for HIV antibodies were still negative. The rate of unspecific reactivities was slightly higher as compared with third-generation assays.

[Risk of HIV-1 or 2 infection associated with transfusion in Benin]

OBJECTIVE

To evaluate the residual risk of transmission of HIV 1/2 infection through transfusion of seronegative blood.

METHODS

This study was carried out between January and July 2000. It was based on eight hundred and twenty-one (821) blood donors screened negative for HIV antibodies by ELISA using Vironostika Uni-form II plus 0 (Organon Teknika). 675 (82.2%) were men and 146 (17.8%) women all aged between 18 and 56 years with a mean age of 25.5 +/- 7.8 years. Serum aliquots of these seronegative blood donor were frozen and further tested with two tests: Enzymun-Test HIV Combi (Roche Immunodiagnostics) and Murex HIV Antigen Mab (Murex).

RESULTS

Twenty six out of 821 (3.2%) seronegative specimens were repeatedly reactive for Enzymun-test. All were tested negative once again for anti-HIV antibodies by ELISA using Vironostika Uni-form II/plus 0. Out of these 26, only one was repeatedly reactive for Murex. For further analysis of the 25 donors tested negative for Murex, only 9 came back for another donation five months later. All of them were tested negative for anti-HIV antibodies by ELISA (Vironostika).

CONCLUSION

Our study shows the existence of residual risk of transmission of HIV1/2 infection associated with transfusion of seronegative blood donors. This risk was higher in our countries compared with industrialised nations. Therefore implementing strategies should be a priority to avoid the residual risk and improve blood transfusion safety.

Insemination with isolated and virologically tested spermatozoa is a safe way for human immunodeficiency type 1 virus?Serodiscordant couples with an infected male partner to have a child

OBJECTIVE

To enable serodiscordant couples to reproduce while minimizing the risk of infecting the female partner and to demonstrate the feasibility of including these couples in an insemination program.

DESIGN

Prospective follow-up study.

SETTING

Ambulatory IUIs.

PATIENT(S)

Fifty-six HIV-1-serodiscordant couples with a male infected partner.

INTERVENTION(S)

Sperm cell separation by the gradient density method followed by the swim-up method, virological detection, and IUI after ovarian stimulation.

MAIN OUTCOME MEASURE(S)

Pregnancy rate, HIV-1 test, and p24 antigenemia in women.

RESULT(S)

Two hundred thirteen IUIs were performed, and 37 pregnancies occurred, resulting in 33 births and 2 ongoing pregnancies. Fifty percent of couples have a child. No women were infected.

CONCLUSION(S)

Our study demonstrates the efficiency of an IUI program with prepared and virologically tested spermatozoa in serodiscordant couples with an HIV-1-infected male partner, allowing the couples to have children without transmission of the virus to the female partner.

Lowering the detection limits of HIV-1 viral load using real-time immuno-PCR for HIV-1 p24 antigen

Presently, the assay that attains maximal sensitivity and dynamic range of HIV-1 viral copy number (50 copies per milliliter) is nucleic acid amplification of HIV RNA in plasma. Enzyme-linked immunosorbent assay (ELISA) methods for quantification of HIV-1 p24 antigen have been relatively insensitive. In this report, we show data that indicate real-time immuno-polymerase chain reaction (IPCR), a combination of the ELISA and PCR techniques, is more sensitive for HIV-1 p24 antigen detection than other currently reported methods. When derived from an IPCR standard curve, a dose response was observed from patient samples with known viral loads diluted within a 3-log range (1.68-6,514 viral RNA copies per milliliter). IPCR detected 42% (22/52) of patient samples that had fewer than 50 viral RNA copies per milliliter by reverse transcriptase-PCR. IPCR shows the potential to become the most analytically sensitive test available for determination of HIV-1 viral load by the detection of HIV-1 p24 antigen.

HIV diagnostic tests: An overview

This article provides an overview of different HIV diagnostic tests, describing how they work and the advantages and limitations of the various tests. This article also briefly reviews the structure and genetic diversity of HIV, the mechanism the virus uses to infect host cells and the different phases of HIV infection. This information is included to facilitate understanding of how HIV diagnostic tests work and what molecular markers these tests use to pinpoint an HIV infection.

Lack of longitudinal intrapatient correlation between p24 antigenemia and levels of human immunodeficiency virus (HIV) type 1 RNA in patients with chronic hiv infection during structured treatment interruptions

Structured treatment interruptions (STIs) have been proposed as a potential treatment strategy during human immunodeficiency virus type 1 (HIV-1) antiretroviral therapy. This still-experimental intervention requires a close monitoring of patients' plasma viremia and CD4(+)-T-cell counts during the treatment interruption phase. By using signal amplification of a heat-dissociated p24 antigen (p24Ag) assay, we compared p24Ag levels with levels of HIV RNA in plasma. One hundred seventy-four plasma samples were obtained from 51 chronically HIV-infected patients: 117 from patients who underwent STIs and 57 from patients who did not. Partial immune complex dissociation and clearance of those complexes by the erythrocytes were also investigated. A significant association between the two assays was observed (beta = 0.23, 95% confidence interval = 0.18, 0.28; P < 0.0001), but the association was smaller in the subset of samples from patients undergoing STIs. Moreover, discordant results and lack of longitudinal intrapatient correlation between levels of p24Ag and HIV-1 RNA were higher in this group. Incomplete immune complex dissociation and binding of those complexes to erythrocytes could be contributing factors involved in the diminished detection of p24Ag. Therefore, signal amplification of a heat-dissociated p24Ag had a positive association with current HIV RNA assays in a population-based analysis. However, it might not be sensitive enough to monitor longitudinal intrapatient viremia during STIs in patients with high CD4(+)-T-cell counts potentially due to the production of high-affinity anti-p24 antibodies and clearance of immune complexes by erythrocytes.

Rapid clearance of virus after acute HIV-1 infection: correlates of risk of AIDS

OBJECTIVE

Our objective was to define early virologic and immunologic determinants of human immunodeficiency virus (HIV) type 1 disease progression among 22 case subjects with acute infection from the Trinidad Seroconvertor Cohort.

METHODS

A linear segmented regression model was fitted to sequential quantitative virus load measurements. Parameters of virus kinetics during different phases of primary infection were correlated with clinical and immunologic end points, by use of Kaplan-Meier estimates and Cox regression.

RESULTS

Ten individuals developed acquired immunodeficiency syndrome (AIDS)-defining events. In univariate analysis, progression to AIDS was associated with rate of initial HIV clearance (P=.002), virus load during set point (P=.008), and CD4(+) cell count during steady state (P=.04). In the multivariate analysis, a rapid rate of initial clearance was the sole independent predictor of subsequent progression to AIDS and was associated with a 92% reduction in the risk of AIDS. The rate of initial clearance is inversely correlated with the number of early symptoms (r=-0.66; P=.0008). However, symptoms did not predict subsequent risk of AIDS.

CONCLUSION

Among a subset of patients, rapid clearance of plasma HIV-1 after peak viremia is associated with lower viral set point, prolonged virus suppression before loss of virologic control, and decreased risk of AIDS. These findings are consistent with the hypothesis that effective immune responses during the earliest phase of infection are important determinants of the subsequent natural history.

First report of human immunodeficiency virus transmission via an RNA-screened blood donation

BACKGROUND AND OBJECTIVES

Blood banks in the USA have recently introduced minipool nucleic acid amplification testing (MP-NAT) of blood products to reduce the transmission of human immunodeficiency virus (HIV) and hepatitis C virus (HCV) by transfusions. However, MP-NAT is limited in its ability to detect preseroconversion samples with very low viral RNA loads.

MATERIALS AND METHODS

To determine whether a red blood cell unit, from an MP-NAT-negative donation, transmitted HIV when transfused to a patient, we compared the viral sequences from the blood donor and recipient. The implicated donation was also tested by commercially available NAT assays at a range of dilution factors to determine whether the infectious unit could have been detected using individual-donation NAT (ID-NAT).

RESULTS

Phylogenetic linkage of HIV sequences in the blood donor and recipient confirmed the transmission of HIV by blood transfusion, the first such case identified since introduction of MP-NAT screening in 1999. Viral RNA was reliably detected by ID-NAT, but only inconsistently detected by MP-NAT.

CONCLUSIONS

Even following the introduction of MP-NAT, a preseroconversion donation with a viral load of <or= 150 copies of RNA/ml went undetected and resulted in an HIV transmission. Implementation of ID-NAT will further reduce such rare transmissions, but at a considerable cost per infectious unit interdicted.