David Kraus

Second-Order Comparison of Gaussian Random Functions and the Geometry of DNA Minicircles

Given two samples of continuous zero-mean iid Gaussian processes on [0,1], we consider the problem of testing whether they share the same covariance structure. Our study is motivated by the problem of determining whether the mechanical properties of short strands of DNA are significantly affected by their base-pair sequence; though expected to be true, had so far not been observed in three-dimensional electron microscopy data. The testing problem is seen to involve aspects of ill-posed inverse problems and a test based on a Karhunen–Loève approximation of the Hilbert–Schmidt distance of the empirical covariance operators is proposed and investigated. When applied to a dataset of DNA minicircles obtained through the electron microscope, our test seems to suggest potential sequence effects on DNA shape. Supplemental material available online.

The J-Curve in HIV: Low and Moderate Alcohol Intake Predicts Mortality but Not the Occurrence of Major Cardiovascular Events.

Objectives:In HIV-negative populations, light-to-moderate alcohol consumption is associated with a lower cardiovascular morbidity and mortality than alcohol abstention. Whether the same holds true for HIV-infected individuals has not been evaluated in detail. Design:Cohort study. Methods:Adults on antiretroviral therapy in the Swiss HIV Cohort Study with follow-up after August 2005 were included. We categorized alcohol consumption into: abstention or very low (<1 g/d), low (1–9 g/d), moderate (10–29 g/d in women and 10–39 g/d in men), and high alcohol intake. Cox proportional hazards models were used to describe the association between alcohol consumption and cardiovascular disease-free survival (combined endpoint), cardiovascular disease events (CADE) and overall survival. Baseline and time-updated risk factors for CADE were included in the models. Results:Among 9741 individuals included, there were 788 events of major CADE or death during 46,719 patient-years of follow-up, corresponding to an incidence of 1.69 events/100 person-years. Follow-up according to alcohol consumption level was 51% no or very low, 20% low, 23% moderate, and 6% high intake. As compared with no or very low alcohol intake, low (hazard ratio 0.79, 95% confidence interval 0.63 to 0.98) and moderate alcohol intakes (0.78, 0.64 to 0.95) were associated with a lower incidence of the combined endpoint. There was no significant association between alcohol consumption and CADE. Conclusions:Compared with no or very low alcohol consumption, low and moderate intake associated with a better CADE-free survival. However, this result was mainly driven by mortality and the specific impact of drinking patterns and type of alcoholic beverage on this outcome remains to be determined.

AIDS defining opportunistic infections in patients with high CD4 counts in the combination antiretroviral therapy (cART) era: things ain't what they used to be.

According to reports from observational databases, classic AIDS‐defining opportunistic infections (ADOIs) occur in patients with CD4 counts above 500/µL on and off cART. Adjudication of these events is usually not performed. However, ADOIs are often used as endpoints, for example, in analyses on when to start cART.

Second-Order Inference for Functional Data with Application to DNA Minicircles

The problem of comparison of second-order (covariance) properties of two samples of random curves is considered. The work is motivated by the study of the mechanical properties of short strands of DNA. Our test is based on the common empirical Karhunen–Loeve expansion and truncated approximation of the Hilbert– Schmidt distance of the empirical covariance operators.

Identifying Nonproportional Covariates in the Cox Model

This paper addresses problem of testing whether an individual covariate in the Cox model has a proportional (i.e., time-constant) effect on the hazard. Two existing methods are considered: one is based on the component of the score process, and the other is a Neyman type smooth test. Simulations show that, when the model contains both proportional and nonproportional covariates, these methods are not reliable tools for discrimination. A simple yet effective solution is proposed based on smooth modeling of the effects of the covariates not in focus.

Ethnicity predicts viral rebound after travel to the tropics in HIV‐infected travelers to the tropics in the Swiss HIV Cohort Study

The number of HIV‐infected individuals from developed countries travelling to tropical and subtropical areas has increased as a result of the clinical and survival benefits of combination antiretroviral therapy. The aim of our study was to describe the traveler population in the SHCS and to determine the frequency of viral rebound in virologically suppressed individuals after a travel episode to the tropics compared to non‐travelers.