Richard Respess

HIV-1 Viral Load Assays for Resource-Limited Settings

The authors discuss studies on the low-cost viral load assays that are currently available and their potential for use in resource-limited settings.

Prevalence of mutations associated with reduced antiretroviral drug susceptibility among human immunodeficiency virus type 1 seroconverters in the United States, 1993-1998

To assess the prevalence of mutations associated with decreased antiretroviral drug susceptibility, specimens were tested from persons infected with human immunodeficiency virus (HIV) during 1993-1998. Subjects were drug naive and were attending sexually transmitted disease clinics in 6 US cities. All were enrolled consecutively and had tested negative for HIV during the 2 years before enrollment. Plasma specimens from patients having >/=1 reverse transcriptase (RT) or primary protease mutation were tested phenotypically with a recombinant virus assay. Of 99 patients, 6 (6%) had mutations associated with zidovudine resistance, 2 (2%) had mutations associated with nonnucleoside RT inhibitor resistance, and 1 (1%) had a primary protease mutation. Overall, the prevalence of resistance-associated primary mutations was 5%, although high levels of decreased drug susceptibility (IC(50)s >/=10 times that of a reference virus) were observed in just 1%. These findings confirm the transmission of these mutations to drug-naive persons.

Antiretroviral Resistance Mutations among Pregnant Human Immunodeficiency Virus Type 1–Infected Women and Their Newborns in the United States: Vertical Transmission and Clades

To assess the impact of antiretroviral resistance on perinatal transmission prevention efforts, human immunodeficiency virus type 1 (HIV-1) genotypic resistance testing was done for 220 HIV-1-infected, zidovudine (AZT)-exposed pregnant women and 24 of their infected infants. The women were prospectively enrolled in 4 US cities in 1991-1997. Phylogenetic and sequencing analyses revealed 5 women with non-clade B infections traced to western African origins. AZT-associated mutations were detected in 17.3% of pregnant women, whereas genotypic resistance to nonnucleoside reverse-transcriptase inhibitors and protease inhibitors was infrequent. No significant association was detected between perinatal transmission and the presence of either AZT or nucleoside reverse-transcriptase inhibitor resistance-associated mutations. AZT resistance mutations were detected in 2 (8.3%) neonatal samples, but the mutation pattern was not identical to the mothers. Although no effect of viral resistance on mother-infant transmission was demonstrated, the advent of more-potent drug classes and the potential for the rapid emergence of resistance warrant prospective surveillance.

Comparison of Two Human Immunodeficiency Virus (HIV) RNA Surrogate Assays to the Standard HIV RNA Assay

ABSTRACT 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 >250,000copies/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.

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

ABSTRACT 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.

Comparative Analysis of Two Commercial Phenotypic Assays for Drug Susceptibility Testing of Human Immunodeficiency Virus Type 1

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) isolates from 50 plasma specimens were analyzed for phenotypic susceptibility to licensed reverse transcriptase inhibitors and protease inhibitors by the Antivirogram and PhenoSense HIV assays. Twenty of these specimens were from recently seroconverted drug-naïve persons, and 30 were from patients who were the sources of occupational exposures to HIV-1; 16 of the specimens in the latter group were from drug-experienced patients. The phenotypic results of the Antivirogram and PhenoSense HIV assays were categorized as sensitive or reduced susceptibility on the basis of the cutoff values established by the manufacturers of each assay. Data for 12 to 15 drugs were available by both assays for 38 specimens and represented a total of 529 pairs of results. The two data sets had a 91.5% concordance by phenotypic category. The discordant results (n = 45) were distributed randomly among 26 specimens and included 28 results (62.2%) which were within a twofold difference of the assay cutoff values. None of the discordant results were associated with primary resistance mutations that predicted high-level (>20-fold) resistance. Discordant results were distributed equally among specimens from drug-experienced and drug-naïve individuals and were slightly higher for protease inhibitors than for nonnucleoside reverse transcriptase inhibitors or nucleoside reverse transcriptase inhibitors. The findings of the present study demonstrate that the results of the Antivirogram and PhenoSense HIV assays correlate well, despite the use of different testing strategies.

Ultrasensitive p24 antigen assay for diagnosis of perinatal human immunodeficiency virus type 1 infection.

ABSTRACT We evaluated an ultrasensitive p24 antigen enzyme immunosorbent assay on 802 plasma specimens from 582 infants and children of 0 to 180 days of age. Overall sensitivity and specificity were 91.7% and 98.5%, respectively. After exclusion of infants of less than 7 days of age, the sensitivity and specificity were 93.7% and 98.3%, respectively.

Antiretroviral Drug Resistance in Human Immunodeficiency Virus–Infected Source Patients for Occupational Exposures to Healthcare Workers

OBJECTIVE To assess the prevalence of HIV antiretroviral resistance among source patients for occupational HIV exposures. DESIGN Blood and data (eg, stage of HIV, previous antiretroviral drug therapy, and HIV RNA viral load) were collected from HIV-infected patients who were source patients for occupational exposures. SETTING Seven tertiary-care medical centers in five U.S. cities (San Diego, California; Miami, Florida; Boston, Massachusetts; Albany, New York; and New York, New York [three sites]) during 1998 to 1999. PARTICIPANTS Sixty-four HIV-infected patients who were source patients for occupational exposures. RESULTS Virus from 50 patients was sequenced; virus from 14 patients with an undetectable (ie, < 400 RNA copies/mL) viral load could not be sequenced. Overall, 19 (38%) of the 50 patients had primary genotypic mutations associated with resistance to reverse transcriptase or protease inhibitors. Eighteen of the 19 viruses with primary mutations and 13 wild type viruses were phenotyped by recombinant assays; 19 had phenotypic resistance to at least one antiretroviral agent. Of the 50 source patients studied, 26 had taken antiretroviral agents in the 3 months before the occupational exposure incident. Sixteen (62%) of the 26 drug-treated patients had virus that was phenotypically resistant to at least one drug. Four (17%) of 23 untreated patients had phenotypically resistant virus. No episodes of HIV transmission were observed among the exposed HCWs. CONCLUSIONS There was a high prevalence of drug-resistant HIV among source patients for occupational HIV exposures. Healthcare providers should use the drug treatment information of source patients when making decisions about post-exposure prophylaxis.