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1.  Marginal Structural Models for Case-Cohort Study Designs to Estimate the Association of Antiretroviral Therapy Initiation With Incident AIDS or Death 
American Journal of Epidemiology  2012;175(5):381-390.
To estimate the association of antiretroviral therapy initiation with incident acquired immunodeficiency syndrome (AIDS) or death while accounting for time-varying confounding in a cost-efficient manner, the authors combined a case-cohort study design with inverse probability-weighted estimation of a marginal structural Cox proportional hazards model. A total of 950 adults who were positive for human immunodeficiency virus type 1 were followed in 2 US cohort studies between 1995 and 2007. In the full cohort, 211 AIDS cases or deaths occurred during 4,456 person-years. In an illustrative 20% random subcohort of 190 participants, 41 AIDS cases or deaths occurred during 861 person-years. Accounting for measured confounders and determinants of dropout by inverse probability weighting, the full cohort hazard ratio was 0.41 (95% confidence interval: 0.26, 0.65) and the case-cohort hazard ratio was 0.47 (95% confidence interval: 0.26, 0.83). Standard multivariable-adjusted hazard ratios were closer to the null, regardless of study design. The precision lost with the case-cohort design was modest given the cost savings. Results from Monte Carlo simulations demonstrated that the proposed approach yields approximately unbiased estimates of the hazard ratio with appropriate confidence interval coverage. Marginal structural model analysis of case-cohort study designs provides a cost-efficient design coupled with an accurate analytic method for research settings in which there is time-varying confounding.
doi:10.1093/aje/kwr346
PMCID: PMC3282878  PMID: 22302074
acquired immunodeficiency syndrome; case-cohort studies; cohort studies; confounding bias; HIV; pharmacoepidemiology; selection bias
2.  The Effects of Opiate Use and Hepatitis C Virus Infection on Risk of Diabetes Mellitus in the Women’s Interagency HIV Study 
Background
Opiate use is common in HIV- and hepatitis C virus (HCV)-infected individuals, however its contribution to the risk of diabetes mellitus is not well understood.
Methods
Prospective study of 1,713 HIV-infected and 652 uninfected participants from the Women’s Interagency HIV Study between October 2000 and March 2006. Diabetes defined as fasting glucose ≥126 mg/dl, or self-report of diabetes medication use or confirmed diabetes diagnosis. Opiate use determined using an interviewer-administered questionnaire. Detectable plasma HCV RNA confirmed HCV infection.
Results
Current opiate users had a higher prevalence of diabetes (15%) than non-users (10%, p=.03), as well as a higher risk of incident diabetes (adjusted relative hazard [RHadj] 1.58, 95% CI 1.01, 2.46), after controlling for HCV infection, HIV/antiretroviral therapy status and diabetes risk factors including age, race/ethnicity, family history of diabetes and body mass index. HCV infection was also an independent risk factor for diabetes (RHadj 1.61, 95% CI 1.02, 2.52). HCV-infected women reporting current opiate use had the highest diabetes incidence (4.83 cases/100 person-years).
Conclusions
Among women with or at-risk for HIV, opiate use is associated with increased diabetes risk independently of HCV infection. Diabetic screening should be part of care for opiate users, and those infected with HCV.
doi:10.1097/QAI.0b013e3181d0c911
PMCID: PMC3069645  PMID: 20190642
opiate use; diabetes mellitus; fasting glucose; Hepatitis C virus; HIV; women
3.  Time Scale and Adjusted Survival Curves for Marginal Structural Cox Models 
American Journal of Epidemiology  2010;171(6):691-700.
Typical applications of marginal structural time-to-event (e.g., Cox) models have used time on study as the time scale. Here, the authors illustrate use of time on treatment as an alternative time scale. In addition, a method is provided for estimating Kaplan-Meier–type survival curves for marginal structural models. For illustration, the authors estimate the total effect of highly active antiretroviral therapy on time to acquired immunodeficiency syndrome (AIDS) or death in 1,498 US men and women infected with human immunodeficiency virus and followed for 6,556 person-years between 1995 and 2002; 323 incident cases of clinical AIDS and 59 deaths occurred. Of the remaining 1,116 participants, 77% were still under observation at the end of follow-up. By using time on study, the hazard ratio for AIDS or death comparing always with never using highly active antiretroviral therapy from the marginal structural model was 0.52 (95% confidence interval: 0.35, 0.76). By using time on treatment, the analogous hazard ratio was 0.44 (95% confidence interval: 0.32, 0.60). In time-to-event analyses, the choice of time scale may have a meaningful impact on estimates of association and precision. In the present example, use of time on treatment yielded a hazard ratio further from the null and more precise than use of time on study as the time scale.
doi:10.1093/aje/kwp418
PMCID: PMC2877453  PMID: 20139124
acquired immunodeficiency syndrome; antiretroviral therapy, highly active; bias (epidemiology); causal inference; confounding factors (epidemiology); proportional hazards model; survival curve; survival time
4.  Using Marginal Structural Measurement-Error Models to Estimate the Long-term Effect of Antiretroviral Therapy on Incident AIDS or Death 
American Journal of Epidemiology  2009;171(1):113-122.
To estimate the net effect of imperfectly measured highly active antiretroviral therapy on incident acquired immunodeficiency syndrome or death, the authors combined inverse probability-of-treatment-and-censoring weighted estimation of a marginal structural Cox model with regression-calibration methods. Between 1995 and 2007, 950 human immunodeficiency virus–positive men and women were followed in 2 US cohort studies. During 4,054 person-years, 374 initiated highly active antiretroviral therapy, 211 developed acquired immunodeficiency syndrome or died, and 173 dropped out. Accounting for measured confounders and determinants of dropout, the weighted hazard ratio for acquired immunodeficiency syndrome or death comparing use of highly active antiretroviral therapy in the prior 2 years with no therapy was 0.36 (95% confidence limits: 0.21, 0.61). This association was relatively constant over follow-up (P = 0.19) and stronger than crude or adjusted hazard ratios of 0.75 and 0.95, respectively. Accounting for measurement error in reported exposure using external validation data on 331 men and women provided a hazard ratio of 0.17, with bias shifted from the hazard ratio to the estimate of precision as seen by the 2.5-fold wider confidence limits (95% confidence limits: 0.06, 0.43). Marginal structural measurement-error models can simultaneously account for 3 major sources of bias in epidemiologic research: validated exposure measurement error, measured selection bias, and measured time-fixed and time-varying confounding.
doi:10.1093/aje/kwp329
PMCID: PMC2800300  PMID: 19934191
acquired immunodeficiency syndrome; bias (epidemiology); cohort studies; confounding factors (epidemiology); epidemiologic measurements; HIV; pharmacoepidemiology; selection bias
5.  Hormonal Contraception and Metabolic Outcomes in Women with or at Risk for HIV Infection 
Introduction
The use of hormonal contraception (HC) is increasing in HIV-infected women. Both HC and HIV infection have been associated with adverse metabolic outcomes. We investigated the association of progestin-only and combined (estrogen/progestin) HC with disorders of glucose and lipid metabolism in HIV-infected and uninfected women.
Methods
Linear mixed models evaluated the association of HC type with fasting HDL, LDL, triglycerides, the homeostasis model assessment estimate of insulin resistance (HOMA-IR), and glucose in 885 HIV-infected and 408 HIV-uninfected women from the Women's Interagency HIV Study seen between October 2000 and September 2005.
Results
Compared to non-HC users, progestin-only HC was independently associated with lower HDL (-3mg/dL;95% confidence interval[CI]:-5,-1 in HIV-infected and -6mg/dL;95% CI:-9,-3 in HIV-uninfected women), greater HOMA (+0.86;95% CI:0.51,1.22 and +0.56;95% CI:0.12,1.01). Combined HC was associated with higher HDL(+5mg/dL;95% CI:2,7 and +5mg/dL;95% CI:3,7).
Conclusion
Progestin–only HC is associated with lower HDL and greater HOMA-IR than non-HC users. Combined HC may be preferred in HIV-infected women of reproductive age at risk for cardiovascular disease, but interactions with antiretroviral therapy that may impair contraceptive efficacy have been reported. Alternative HC methods that minimize adverse outcomes but maintain efficacy require further study.
PMCID: PMC2886798  PMID: 19950431
HIV/AIDS; hormonal contraception; Depo Provera®; HDL; triglycerides

Results 1-5 (5)