To the Editor:
I read the paper by Cohoon et al
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with interest. The authors conducted a case-control study to know if infection was a risk factor for venous thromboembolism. Incident deep vein thrombosis or pulmonary embolism was registered and 1:2 matching was conducted for case and control setting by considering age and sex. The authors adjusted 17 independent variables for conducting conditional logistic regression analysis. Adjusted odds ratio (95% confidence interval [CI]) of infection for venous thromboembolism was 4.5 (3.6-5.5). They also specified the risk of specific sites of infection for venous thromboembolism. I have some concerns about their study.First, the authors adopted a conditional logistic regression model. Although 1:2 matching was conducted, the lack of control data was obvious. There is a risk of unstable estimate if the number of controls is lost. Instead, using enough numbers of controls has an advantage of stable estimate for the outcome,
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especially in stratification of independent variables. Wide ranges of 95% CI would partly reflect unstable estimate.Second, the authors did not evaluate the cause of infection in their study. Frasson et al
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conducted a survey on the cause of infection in patients with venous thromboembolism, with special reference to site of infection and immobility. They followed up for at least 3 months, and the patients with respiratory tract infections were more likely than those with other types of infection to have pulmonary embolism. In addition, infection contributing to the pathogenesis of venous thromboembolism was significantly accelerated by immobility. As there is no definite result by a meta-analysis,4
further studies with special reference to immobility are needed to know the association between infection and venous thromboembolism.Finally, Kaplan et al
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conducted a prospective study on the incidence of venous thromboembolism during severe sepsis and septic shock. The incidence was 37.2% (95% CI, 28.3-46.8), but the risk of mortality was not significantly associated with venous thromboembolism. I recommend that Cohoon et al include the severity of infection in relation to venous thromboembolism.References
- Is infection an independent risk factor for venous thromboembolism? A population-based, case-control study.Am J Med. 2018; 131: 307-316
- Case-control studies: matched controls or all available controls?.J Clin Epidemiol. 1994; 47: 971-975
- Infection as cause of immobility and occurrence of venous thromboembolism: analysis of 1635 medical cases from the RIETE registry.J Thromb Thrombolysis. 2016; 41: 404-412
- A systematic review of mobility/immobility in thromboembolism risk assessment models for hospitalized patients.J Thromb Thrombolysis. 2017; 44: 94-103
- VTE incidence and risk factors in patients with severe sepsis and septic shock.Chest. 2015; 148: 1224-1230
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