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AIDS Cohort Study (aid + cohort_study)

Distribution by Scientific Domains

Life Sciences	40%

Selected Abstracts

Assessing immunophenotyping performance: Proficiency-validation for adopting improved flow cytometry methods

CYTOMETRY, Issue 4 2007
Lance E. Hultin
Abstract Background: The continuous improvement and evolution of immune cell phenotyping requires periodic upgrading of laboratory methods and technology. Flow cytometry laboratories that are participating in research protocols sponsored by the NIAID are required to perform "switch" studies to validate performance before methods for T-cell subset analysis can be changed. Methods: Switch studies were conducted among the four flow cytometry laboratories of the Multicenter AIDS Cohort Study (MACS), comparing a 2-color, lyse-wash method and a newer, 3-color, lyse no-wash method. Two of the laboratories twice failed to satisfy the criteria for acceptable differences from the previous method. Rather than repeating more switch studies, these laboratories were allowed to adopt the 3-color, lyse no-wash method. To evaluate the impact of the switch to the new method at these two sites, their results with the new method were evaluated within the context of all laboratories participating in the NIH-NIAID-Division of AIDS Immunology Quality Assurance (IQA) proficiency-testing program. Results: Laboratory performance at these two sites substantially improved relative to the IQA standard test results. Variation across the four MACS sites and across replicate samples was also reduced. Conclusions: Although switch studies are the conventional method for assessing comparability of laboratory methods, two alternatives to the requirement of repeating failed switch studies should be considered: (1) test the new method and assess performance on the proficiency testing reference panel, and (2) prior to adoption of the new methods, use both the old and the new method on the reference panel samples and demonstrate that performance with the new method is better according to standard statistical procedures. These alternatives may help some laboratories' transition to a new and superior methodology more quickly than if they are required to attempt multiple, serial switch studies. © 2007 Clinical Cytometry Society [source]

Investigation of pre-diagnostic virological markers for progressive multifocal leukoencephalopathy in human immunodeficiency virus-infected patients

JOURNAL OF MEDICAL VIROLOGY, Issue 7 2009
Mary K. Grabowski
Abstract Progressive multifocal leukoencephalopathy (PML) is a severe neurological disorder due to JC virus (JCV) infection. Pre-diagnostic biological markers and risk factors for PML are not well understood. We conducted a case,control study nested within the Multicenter AIDS Cohort Study to examine the association between JCV viruria and viremia and serum antibody to JCV capsids, in relation to subsequent PML diagnoses, 5 months to 12 years later. Other demographic and immunologic factors were also examined. The study population included 28 incident cases of PML, 26 matched HIV-positive controls, and 50 HIV-negative controls. Prevalence of JCV viruria was 37% in cases, 42% in HIV-positive controls, and 28% in HIV-negative controls (P,=,0.43). Among persons with JCV viruria, persistent viruria was more common in cases (89%) than in HIV-positive controls (33%) (P,=,0.02). Presence of JCV viruria was not related to the time to PML diagnosis (OR: 1.03, 95% CI: 0.8,1.4); however, the urinary concentration of JCV DNA increased with proximity to the date of PML diagnosis in cases. JCV seropositivity did not differ between cases or controls (P,=,0.42). Four cases tested JCV seronegative, including one case only 5 months prior to diagnosis with PML. JCV DNA was detected in the serum of one HIV-positive control. Smoking was the only demographic variable analyzed associated with an increased risk for PML (MOR: 9.0, 95% CI: 1.2,394.5). The results suggest that persistent JCV viruria and increasing urinary concentration of JCV DNA may be predictive of PML for some patients. J. Med. Virol. 81:1140,1150, 2009. © 2009 Wiley-Liss, Inc. [source]

Semiparametric Analysis for Recurrent Event Data with Time-Dependent Covariates and Informative Censoring

BIOMETRICS, Issue 1 2010
C.-Y. Huang
Summary Recurrent event data analyses are usually conducted under the assumption that the censoring time is independent of the recurrent event process. In many applications the censoring time can be informative about the underlying recurrent event process, especially in situations where a correlated failure event could potentially terminate the observation of recurrent events. In this article, we consider a semiparametric model of recurrent event data that allows correlations between censoring times and recurrent event process via frailty. This flexible framework incorporates both time-dependent and time-independent covariates in the formulation, while leaving the distributions of frailty and censoring times unspecified. We propose a novel semiparametric inference procedure that depends on neither the frailty nor the censoring time distribution. Large sample properties of the regression parameter estimates and the estimated baseline cumulative intensity functions are studied. Numerical studies demonstrate that the proposed methodology performs well for realistic sample sizes. An analysis of hospitalization data for patients in an AIDS cohort study is presented to illustrate the proposed method. [source]

Regression Analysis of Doubly Censored Failure Time Data Using the Additive Hazards Model

BIOMETRICS, Issue 3 2004
Liuquan Sun
Summary Doubly censored failure time data arise when the survival time of interest is the elapsed time between two related events and observations on occurrences of both events could be censored. Regression analysis of doubly censored data has recently attracted considerable attention and for this a few methods have been proposed (Kim et al., 1993, Biometrics49, 13,22; Sun et al., 1999, Biometrics55, 909,914; Pan, 2001, Biometrics57, 1245,1250). However, all of the methods are based on the proportional hazards model and it is well known that the proportional hazards model may not fit failure time data well sometimes. This article investigates regression analysis of such data using the additive hazards model and an estimating equation approach is proposed for inference about regression parameters of interest. The proposed method can be easily implemented and the properties of the proposed estimates of regression parameters are established. The method is applied to a set of doubly censored data from an AIDS cohort study. [source]

Nonparametric Estimation for the Three-Stage Irreversible Illness,Death Model

BIOMETRICS, Issue 3 2000
Somnath Datta
Summary. In this paper, we present new nonparametric estimators of the stage-occupation probabilities in the three-stage irreversible illness-death model. These estimators use a fractional risk set and a reweighting approach and are valid under stage-dependent censoring. Using a simulated data set, we compare the behavior of our estimators with previously proposed estimators. We also apply our estimators to data on time to Pneumocystis pneumonia and death obtained from an AIDS cohort study. [source]