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Follow-up Samples (follow-up + sample)
Selected AbstractsDetection of drug resistance mutations as a predictor of subsequent virological failure in patients with HIV-1 viral rebounds of less than 1,000 RNA copies/mlJOURNAL OF MEDICAL VIROLOGY, Issue 9 2007Chris Verhofstede Abstract In order to evaluate the usefulness of resistance testing after a viral rebound with plasma HIV RNA levels of less than 1,000 copies (c)/ml, genotyping was performed on 39 samples from patients on highly active antiretroviral therapy (HAART) showing a viremia of over 50 c/ml up to a maximum of 1,000 c/ml after at least one undetectable viral load result. Protease and reverse transcriptase (RT) sequences were obtained for all 39 samples. In 10 (25.6%) of the samples, mutations not seen before the initiation of the regimen were observed. The M184V/I mutation was the most prevalent but in several patients a combination of multiple mutations was detected. Follow-up samples were available for 34 patients. In six (85.71%) out of seven patients with new mutations, the viral load on the follow-up visit remained detectable, indicating true failure, compared to 6 (31.6%) true failures out of 19 patients in whom only wild type virus was detected (P,=,0.02) and three (37.5%) out of eight patients in whom only the mutations already present at the initiation of HAART were seen (P,=,0.08). The results indicate that reliable resistance testing can be performed on samples with a viral burden of less than 1,000 c/ml and demonstrate that multiple drug resistance mutations can be selected at low viral load rebounds. Most importantly, detection of resistance mutations in viral rebound samples was predictive of subsequent virological failure. J. Med. Virol. 79:1254,1260, 2007. © Wiley-Liss, Inc. [source] Feasibility and validity of low-budget telephonic follow-up interviews in routine outcome monitoring of substance abuse treatmentADDICTION, Issue 7 2009Suzan C.C. Oudejans ABSTRACT Aims Routine outcome monitoring (ROM) is receiving growing attention. However, follow-up interviews are time-consuming and costly. This study examines the feasibility and validity of low-budget telephonic follow-up interviews for ROM in a substance abuse treatment centre (SATC). Design Observational study using data collected for routine outcome monitoring. Setting The study was performed in a SATC in an urban area in the Netherlands. Participants Feasibility and validity were assessed on data of 2325 patients. Measurements Data on pre-treatment socio-demographic and clinical characteristics were collected using electronic patient records (EPRs) and the European version of the Addiction Severity Index (EuropASI). Data on intensity of treatment were also collected through the EPRs. Telephonic follow-up interviews were conducted between 9 and 10 months after intake. Findings A 53% follow-up rate was achieved; 35% of the patients could not be contacted, 3% explicitly refused and in 8% other reasons accounted for non-participation. About 50% of the interviews took place in the intended time-frame. Costs were ,40 ($57) per completed interview. There were indications of selection bias, because patients with cocaine as their primary problem and patients with polysubstance abuse were under-represented in the follow-up sample; the presence of these disorders is associated with negative treatment outcome. Conclusions Implementing telephonic low-budget follow-up interviews for ROM is feasible, but selection bias threatens internal validity of data, limiting generalization to the total treatment population. Increased efforts to track patients for follow-up may improve generalization. [source] Addressing an Idiosyncrasy in Estimating Survival Curves Using Double Sampling in the Presence of Self-Selected Right CensoringBIOMETRICS, Issue 2 2001Constantine E. Frangakis Summary. We investigate the use of follow-up samples of individuals to estimate survival curves from studies that are subject to right censoring from two sources: (i) early termination of the study, namely, administrative censoring, or (ii) censoring due to lost data prior to administrative censoring, so-called dropout. We assume that, for the full cohort of individuals, administrative censoring times are independent of the subjects' inherent characteristics, including survival time. To address the loss to censoring due to dropout, which we allow to be possibly selective, we consider an intensive second phase of the study where a representative sample of the originally lost subjects is subsequently followed and their data recorded. As with double-sampling designs in survey methodology, the objective is to provide data on a representative subset of the dropouts. Despite assumed full response from the follow-up sample, we show that, in general in our setting, administrative censoring times are not independent of survival times within the two subgroups, nondropouts and sampled dropouts. As a result, the stratified Kaplan,Meier estimator is not appropriate for the cohort survival curve. Moreover, using the concept of potential outcomes, as opposed to observed outcomes, and thereby explicitly formulating the problem as a missing data problem, reveals and addresses these complications. We present an estimation method based on the likelihood of an easily observed subset of the data and study its properties analytically for large samples. We evaluate our method in a realistic situation by simulating data that match published margins on survival and dropout from an actual hip-replacement study. Limitations and extensions of our design and analytic method are discussed. [source] Validation of MCADD newborn screeningCLINICAL GENETICS, Issue 2 2009EM Maier Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) represents a potentially fatal fatty acid ,-oxidation disorder. Newborn screening (NBS) by tandem mass spectrometry (MS/MS) has been implemented worldwide, but is associated with unresolved questions regarding population heterogeneity, burden on healthy carriers, cut-off policies, false-positive and negative rates. In a retrospective case-control study, 333 NBS samples showing borderline acylcarnitine patterns but not reaching recall criteria were genotyped for the two most common mutations (c.985A>G/c.199C>T) and compared with genotypes and acylcarnitines of 333 controls, 68 false-positives, and 34 patients. c.985A>G was more frequently identified in the study group and false-positives compared to controls (1:4.3/1:2.3 vs. 1:42), whereas c.199C>T was found more frequently only within the false-positives (1:23). Biochemical criteria were devised to differentiate homozygous (c.985A>G), compound heterozygous (c.985A>G/c.199C>T), and heterozygous individuals. Four false-negatives were identified because our initial algorithm required an elevation of octanoylcarnitine (C8) and three secondary markers in the initial and follow-up sample. The new approach allowed a reduction of false-positives (by defining high cut-offs: 1.4 ,mol/l for C8; 7 for C8/C12) and false-negatives (by sequencing the ACADM gene of few suspicious samples). Our validation strategy is able to differentiate healthy carriers from patients doubling the positive predictive value (42,88%) and to target NBS to MCADD-subsets with potentially higher risk of adverse outcome. It remains controversial, if NBS programs should aim at identifying all subsets of all diseases included. Because the natural course of milder variants cannot be assessed by observational studies, our strategy could serve as a general model for evaluation of MS/MS-based NBS. [source] Re-estimating the prevalence of psychiatric disorders in a nationally representative sample of persons receiving care for HIV: results from the HIV cost and services utilization studyINTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 2 2002PhD Maria Orlando Abstract The objective of this study was to obtain accurate estimates of the prevalence of psychiatric disorder in the population represented by the HIV Costs and Services Utilization Study cohort. We constructed logistic regression models to predict DSM-IV diagnoses of depression, generalized anxiety disorder, panic, and dysthymia among a subsample of the HCSUS cohort who in separate interviews completed the CIDI-SF and the full CIDI diagnostic interview. Diagnoses were predicted using responses to the CIDI-SF as well as other variables contained in the baseline and first follow-up interviews. Resulting regression equations were applied to the entire baseline and first follow-up samples to obtain new estimates of the prevalence of disorder. Compared to estimates based on the CIDI-SF alone, estimates obtained from this procedure provide a more accurate representation of the prevalence of the presence of any one of these four psychiatric disorders in this population, yielding more correct classifications and a lower false-positive rate. Prevalence rates reported in this study are as much as 16% lower than rates estimated using the CIDI-SF alone, but are still considerably higher than estimates for the general community population. Copyright © 2002 Whurr Publishers Ltd. [source] Concurrence of hepatitis B surface antibodies and surface antigen: implications for postvaccination control of health care workersJOURNAL OF VIRAL HEPATITIS, Issue 2 2002H. L. Zaaijer Among 1081 persons testing positive for hepatitis B surface antigen, 106 (10%) tested positive for antibodies to surface antigen (anti-HBs) in the same blood sample. Thirty of these persons were studied in detail: seven tested positive for hepatitis B e-antigen, nine were apparently healthy blood donors, and in 14 chronic infection could be demonstrated in follow-up samples. Frozen samples of 14 persons were available for additional quantitative anti-HBs testing using another anti-HBs assay: three showed no anti-HBs reactivity, seven showed borderline anti-HBs levels (1,5 IU/L), and anti-HBs titres ranged from 23 to 66 IU/L in four HBsAg-positive persons, including an apparently healthy blood donor. Thus, after hepatitis B vaccination of medical personnel, presence of anti-HBs may erroneously suggest immunity, while in fact chronic infection with hepatitis B virus is present. [source] Primary infection with the Epstein-Barr virus and risk of multiple sclerosis,ANNALS OF NEUROLOGY, Issue 6 2010Lynn I. Levin PhD To determine whether multiple sclerosis (MS) risk increases following primary infection with the Epstein-Barr virus (EBV), we conducted a nested case-control study including 305 individuals who developed MS and 610 matched controls selected among the >8 million active-duty military personnel whose serum has been stored in the Department of Defense Serum Repository. Time of EBV infection was determined by measuring antibody titers in serial serum samples collected before MS onset among cases, and on matched dates among controls. Ten (3.3%) cases and 32 (5.2%) controls were initially EBV negative. All of the 10 EBV-negative cases became EBV positive before MS onset; in contrast, only 35.7% (n = 10) of the 28 controls with follow-up samples seroconverted (exact p value = 0.0008). We conclude that MS risk is extremely low among individuals not infected with EBV, but it increases sharply in the same individuals following EBV infection. ANN NEUROL 2010;67:824,830 [source] Addressing an Idiosyncrasy in Estimating Survival Curves Using Double Sampling in the Presence of Self-Selected Right CensoringBIOMETRICS, Issue 2 2001Constantine E. Frangakis Summary. We investigate the use of follow-up samples of individuals to estimate survival curves from studies that are subject to right censoring from two sources: (i) early termination of the study, namely, administrative censoring, or (ii) censoring due to lost data prior to administrative censoring, so-called dropout. We assume that, for the full cohort of individuals, administrative censoring times are independent of the subjects' inherent characteristics, including survival time. To address the loss to censoring due to dropout, which we allow to be possibly selective, we consider an intensive second phase of the study where a representative sample of the originally lost subjects is subsequently followed and their data recorded. As with double-sampling designs in survey methodology, the objective is to provide data on a representative subset of the dropouts. Despite assumed full response from the follow-up sample, we show that, in general in our setting, administrative censoring times are not independent of survival times within the two subgroups, nondropouts and sampled dropouts. As a result, the stratified Kaplan,Meier estimator is not appropriate for the cohort survival curve. Moreover, using the concept of potential outcomes, as opposed to observed outcomes, and thereby explicitly formulating the problem as a missing data problem, reveals and addresses these complications. We present an estimation method based on the likelihood of an easily observed subset of the data and study its properties analytically for large samples. We evaluate our method in a realistic situation by simulating data that match published margins on survival and dropout from an actual hip-replacement study. Limitations and extensions of our design and analytic method are discussed. [source] Monitoring gastric lymphoma in peripheral blood by quantitative IgH allele-specific oligonucleotide real-time PCR and API2-MALT1 PCRBRITISH JOURNAL OF HAEMATOLOGY, Issue 5 2005M. I. Schreuder Summary Gastric extranodal marginal zone lymphoma (EMZL) often shows prolonged localised disease, but the present study demonstrated the presence of tumour cells in peripheral blood (PB) of low stage patients. We studied the presence of tumour cells in PB in gastric lymphoma patients harbouring or lacking t(11;18)(q21;q21), by real-time immunoglobulin (Ig)H allele-specific oligonucleotide-polymerase chain reaction (ASO-PCR) and API2-MALT1 PCR. Tumour cells were exclusively detected in PB of t(11;18)(q21;q21)+ -EMZL patients. The presence of tumour cells in PB and gastric biopsy follow-up samples showed a good correlation in these patients, suggesting clinical relevance for monitoring of tumour cells in PB of gastric t(11;18)(q21;q21)+ -EMZL patients. [source] | |||||||||||||