Previous diagnoses of cancer, surgery (including trauma and fracture) and pregnancy were included only in the analysis for overall VTE (the latter two as time-dependent variables). Diagnoses of cancer, diabetes mellitus, myocardial infarction, heart failure, stroke, psychiatric diseases (as a surrogate for the use of neuroleptic drugs) and obesity,

as well Cell Cycle inhibitor as surgery and pregnancy, were extracted from the DNHR. We first assessed the impact of HIV infection on the risk of being diagnosed with VTE, both overall and separately for unprovoked and provoked thrombotic episodes. Because both HIV infection and VTE may be strongly associated with IDU, all analyses were stratified by IDU. Time was computed from index date until date of VTE, death, emigration, loss to follow-up or 1 January 2008, whichever came first. We used a cumulative incidence function to illustrate time to first VTE, recognizing death as a competing risk.

We calculated the incidence rates (IRs) and 95% confidence intervals (CIs) for VTE. We used time-updated Cox regression Fludarabine solubility dmso analysis to compute incidence rate ratios (IRRs) as estimates of the relative risk for VTE in the non-IDU and the IDU groups compared with the general population cohort. To examine the combined impact of immunodeficiency (CD4 count<200 cells/μL) and HAART on the risk of VTE in the HIV-infected group, we used time-dependent Cox regression analysis to compute IRRs. In the latter analysis the IRR was compared with an observed time when the HIV-infected patients were not on HAART and had a CD4 count>200 cells/μL. In all models, we controlled for gender, age at index date (categorized in five age intervals: 0–15, 16–30, 31–45, 46–60, and Montelukast Sodium 60+years) and calendar year (categorized in four time intervals: 1995–1997, 1998–2000, 2001–2003, and 2004–2007) as well as diabetes, myocardial infarction, heart failure, stroke, psychiatric diagnoses and obesity. Statistical analyses were performed using sas version 9.1 (SAS

Institute, Cary, NC, USA). The study was approved by the Danish Data Protection Agency. We identified 4333 HIV-infected patients and 43 330 individuals in the general population cohort. The median age on the index date was 36.6 years and 76.6% were male. IDU was reported as the mode of infection in 482 HIV-infected patients (11.1%). Additional characteristics of IDU and non-IDU HIV-infected patients and population cohort individuals are provided in Table 1. During the study period we observed 148 (3.4%) first episodes of VTE in the HIV-infected group, of which 56 (37.8%) occurred in the IDU group (83.9% unprovoked) and 92 (62.2%) occurred in the non-IDU group (73.9% unprovoked). In comparison, 371 (0.9%) episodes of VTE occurred in the population control cohort (79.2% unprovoked). The median age at diagnosis of VTE in the non-IDU group [46.4 years; interquartile range (IQR) 36.5–55.