The cryptococcal antigen lateral flow assay: A point-of-care diagnostic at an opportune time.

Cryptococcal meningitis is a devastating HIV-related opportunistic infection, affecting nearly 1 million individuals and causing over 500 000 deaths each year. The burden of disease is greatest in sub-Saharan Africa and Southeast Asia, where cryptococcal disease is the most common cause of meningitis. Rapid, accurate and affordable diagnosis of cryptococcal disease has been lacking in many of the most heavily affected areas. Here, we review a point-of-care assay for cryptococcal disease, the dipstick-formatted cryptococcal antigen lateral flow assay (LFA) (IMMY, Norman, OK). In comparison to culture, the assay is 99.5% sensitive and 98% specific. In comparison to other commercially available tests for cryptococcal antigen, the LFA has equal or superior sensitivity and specificity in CSF, plasma and serum samples. We discuss potential applications for the use of the assay in resource-limited settings, including what is likely to be an important role of the LFA in screening for early cryptococcal infection before clinical disease and in evaluating pre-emptive treatment.

Nucleoside reverse transcriptase inhibitor resistance mutations associated with first-line stavudine-containing antiretroviral therapy: programmatic implications for countries phasing out stavudine.

BACKGROUND: The World Health Organization Antiretroviral Treatment Guidelines recommend phasing-out stavudine because of its risk of long-term toxicity. There are two mutational pathways of stavudine resistance with different implications for zidovudine and tenofovir cross-resistance, the primary candidates for replacing stavudine. However, because resistance testing is rarely available in resource-limited settings, it is critical to identify the cross-resistance patterns associated with first-line stavudine failure. METHODS: We analyzed HIV-1 resistance mutations following first-line stavudine failure from 35 publications comprising 1,825 individuals. We also assessed the influence of concomitant nevirapine vs. efavirenz, therapy duration, and HIV-1 subtype on the proportions of mutations associated with zidovudine vs. tenofovir cross-resistance. RESULTS: Mutations with preferential zidovudine activity, K65R or K70E, occurred in 5.3% of individuals. Mutations with preferential tenofovir activity, ≥ two thymidine analog mutations (TAMs) or Q151M, occurred in 22% of individuals. Nevirapine increased the risk of TAMs, K65R, and Q151M. Longer therapy increased the risk of TAMs and Q151M but not K65R. Subtype C and CRF01_AE increased the risk of K65R, but only CRF01_AE increased the risk of K65R without Q151M. CONCLUSIONS: Regardless of concomitant nevirapine vs. efavirenz, therapy duration, or subtype, tenofovir was more likely than zidovudine to retain antiviral activity following first-line d4T therapy.

A review of the virological efficacy of the 4 World Health Organization-recommended tenofovir-containing regimens for initial HIV therapy.

We systematically reviewed studies of the virological efficacy of the 4 new tenofovir (TDF)-containing regimens recommended for initial antiretroviral (ARV) therapy in the 2010 World Health Organization ARV Treatment Guidelines. Thirty-three studies assessed the efficacy of 1 or more TDF-containing regimens: TDF/lamivudine (3TC)/nevirapine (NVP) (n = 3), TDF/ emtricitabine (FTC)/NVP (n = 9), TDF/3TC/efavirenz (EFV) (n = 6), and TDF/FTC/EFV (n = 19). TDF/3TC/NVP was the least well-studied and appeared the least efficacious of the 4 regimens. In 2 comparative studies, TDF/3TC/NVP was associated with significantly more virological failure than AZT/3TC/NVP; a third study was terminated prematurely because of early virological failure. TDF/FTC/NVP was either equivalent or inferior to its comparator arms. TDF/3TC/EFV was equivalent to its comparator arms. TDF/FTC/EFV was equivalent or superior to its comparator arms. Possible explanations for these findings include the greater antiviral activity of EFV versus NVP and longer intracellular half-life of FTC-triphosphate versus 3TC-triphosphate. Further study of TDF/3TC/NVP is required before it is widely deployed for initial ARV therapy.

The HIVdb system for HIV-1 genotypic resistance interpretation.

The Stanford HIV Drug Resistance Database hosts a freely available online genotypic resistance interpretation system called HIVdb to help clinicians and laboratories interpret HIV-1 genotypic resistance tests. These tests are designed to assess susceptibility to nucleoside and nonnucleoside reverse transcriptase inhibitors (NRTI and NNRTI), protease inhibitors and integrase inhibitors. The HIVdb genotypic resistance interpretation system output consists of (1) a list of penalty scores for each antiretroviral (ARV) resistance mutation in a submitted sequence, (2) estimates of decreased NRTI, NNRTI, protease and integrase inhibitor susceptibility, and (3) comments about each ARV resistance mutation in the submitted sequence. The application's strengths are its convenience for submitting sequences, its quality control analysis, its transparency and its extensive comments. The Sierra Web service is an extension that enables laboratories analyzing many sequences to individualize the format of their results. The algorithm specification interface compiler makes it possible for HIVdb to provide results using a variety of different HIV-1 genotypic resistance interpretation algorithms.

HIV-1 antiretroviral resistance: scientific principles and clinical applications.

The efficacy of an antiretroviral (ARV) treatment regimen depends on the activity of the regimen's individual ARV drugs and the number of HIV-1 mutations required for the development of resistance to each ARV - the genetic barrier to resistance. ARV resistance impairs the response to therapy in patients with transmitted resistance, unsuccessful initial ARV therapy and multiple virological failures. Genotypic resistance testing is used to identify transmitted drug resistance, provide insight into the reasons for virological failure in treated patients, and help guide second-line and salvage therapies. In patients with transmitted drug resistance, the virological response to a regimen selected on the basis of standard genotypic testing approaches the responses observed in patients with wild-type viruses. However, because such patients are at a higher risk of harbouring minority drug-resistant variants, initial ARV therapy in this population should contain a boosted protease inhibitor (PI) - the drug class with the highest genetic barrier to resistance. In patients receiving an initial ARV regimen with a high genetic barrier to resistance, the most common reasons for virological failure are nonadherence and, potentially, pharmacokinetic factors or minority transmitted drug-resistant variants. Among patients in whom first-line ARVs have failed, the patterns of drug-resistance mutations and cross-resistance are often predictable. However, the extent of drug resistance correlates with the duration of uncontrolled virological replication. Second-line therapy should include the continued use of a dual nucleoside/nucleotide reverse transcriptase inhibitor (NRTI)-containing backbone, together with a change in the non-NRTI component, most often to an ARV belonging to a new drug class. The number of available fully active ARVs is often diminished with each successive treatment failure. Therefore, a salvage regimen is likely to be more complicated in that it may require multiple ARVs with partial residual activity and compromised genetic barriers of resistance to attain complete virological suppression. A thorough examination of the patient's ARV history and prior resistance tests should be performed because genotypic and/or phenotypic susceptibility testing is often not sufficient to identify drug-resistant variants that emerged during past therapies and may still pose a threat to a new regimen. Phenotypic testing is also often helpful in this subset of patients. ARVs used for salvage therapy can be placed into the following hierarchy: (i) ARVs belonging to a previously unused drug class; (ii) ARVs belonging to a previously used drug class that maintain significant residual antiviral activity; (iii) NRTI combinations, as these often appear to retain in vivo virological activity, even in the presence of reduced in vitro NRTI susceptibility; and rarely (iv) ARVs associated with previous virological failure and drug resistance that appear to have possibly regained their activity as a result of viral reversion to wild type. Understanding the basic principles of HIV drug resistance is helpful in guiding individual clinical decisions and the development of ARV treatment guidelines.