Intensive care unit (ICU)-acquired bacteraemia and ICU mortality and discharge: addressing time-varying confounding using appropriate methodology. Issue 1 (May 2018)

• Record Type: Journal Article
• Authors: Pouwels, K.B.; Vansteelandt, S.; Batra, R.; Edgeworth, J.D.; Smieszek, T.; Robotham, J.V.
• Is Part Of: Journal of hospital infection. Volume 99:Issue 1(2018)
• Page Start: 42
• Page End: 47
• Publication Date: 2018-05
• Subjects: Burden -- Intensive care units -- Bacteraemia -- Inverse probability weighting -- Bias; Cross infection -- Periodicals; Cross infection -- Prevention -- Periodicals; Nosocomial infections -- Periodicals; Nosocomial infections -- Prevention -- Periodicals; Cross Infection -- Periodicals; Cross Infection -- prevention & control -- Periodicals; Infection Control -- Periodicals; Electronic journals; 614.44
• DOI: 10.1016/j.jhin.2017.11.011
• Languages: English
• ISSNs: 0195-6701

Abstract

Summary: Background: Studies often ignore time-varying confounding or may use inappropriate methodology to adjust for time-varying confounding. Aim: To estimate the effect of intensive care unit (ICU)-acquired bacteraemia on ICU mortality and discharge using appropriate methodology. Methods: Marginal structural models with inverse probability weighting were used to estimate the ICU mortality and discharge associated with ICU-acquired bacteraemia among patients who stayed more than two days at the general ICU of a London teaching hospital and remained bacteraemia-free during those first two days. For comparison, the same associations were evaluated with (i) a conventional Cox model, adjusting only for baseline confounders and (ii) a Cox model adjusting for baseline and time-varying confounders. Findings: Using the marginal structural model with inverse probability weighting, bacteraemia was associated with an increase in ICU mortality (cause-specific hazard ratio (CSHR): 1.29; 95% confidence interval (CI): 1.02–1.63) and a decrease in discharge (CSHR: 0.52; 95% CI: 0.45–0.60). By 60 days, among patients still in the ICU after two days and without prior bacteraemia, 8.0% of ICU deaths could be prevented by preventing all ICU-acquired bacteraemia cases. The conventional Cox model adjusting for time-varying confounders gave substantially different results [for ICU mortality, CSHR: 1.08 (95% CI: 0.88–1.32); for discharge, CSHR: 0.68 (95% CI: 0.60–0.77)]. Conclusion: In this study, even after adjusting for the timing of acquiring bacteraemia and time-varying confounding using inverse probability weighting for marginal structural models, ICU-acquired bacteraemia was associated with a decreased daily ICU discharge risk and an increased risk of ICU mortality.