Recent respiratory infection and risk of venous thromboembolism: case–control study through a general practice database

BACKGROUND The association between respiratory infection and risk of heart attacks and strokes is well established. However, less evidence exists for an association between respiratory infection and venous thromboembolism (VTE). In this article, we describe the associations between respiratory infection and VTE. METHODS All cases aged ≥18 years of first-time diagnosis of deep-vein thrombosis (DVT) or pulmonary embolism (PE) were identified together with single-matched controls from a primary care general practice database. In addition to the matching characteristics, information was collected on other potentially important confounding factors. RESULTS There were 457/11,557 (4.0%) DVT cases with respiratory infection in the year before the index date (73 in the preceding month) compared with 262/11,557 (2.3%) controls (24 in the preceding month). There was an increased risk of DVT in the month following infection [adjusted odds ratio (OR) = 2.64, 95% confidence interval (95% CI) 1.62-4.29] which persisted up to a year. There were 180/5162 (3.5%) PE cases with respiratory infection in the year before the index date compared with 94/5162 (1.8%) controls excluding those in the preceding month to avoid the possible misdiagnosis of early PE. There was an increased risk of PE in the 3 months following infection (adjusted OR = 2.50, 95% CI 1.33-4.72) which may have persisted up to a year. CONCLUSIONS There are strong associations between recent respiratory infection and VTE. There should be less distinction between venous and arterial events in decisions about preventing or aborting infections, especially in high-risk patients.