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ICU-acquired bacteraemia and ICU mortality and discharge: addressing time-varying confounding using appropriate methodology

Research output: Contribution to journalArticle

Koen B. Pouwels, Stijn Vansteelandt, Rahul Batra, Jonathan D. Edgeworth, Timo Smieszek, Julie V. Robotham

Original languageEnglish
JournalJournal of Hospital Infection
Early online date23 Nov 2017
DOIs
Accepted/In press17 Nov 2017
E-pub ahead of print23 Nov 2017

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Abstract

Background Studies often ignore time-varying confounding or use inappropriate methodology to adjust for time-varying confounding. Aim We estimated the effect of 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 2 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 1) a conventional Cox model, adjusting for only baseline confounders and 2) 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% 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 2 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: CSHR 1.08 (95% CI 0.88-1.32) for ICU mortality and CSHR 0.68 (95% CI 0.60-0.77) for discharge. Conclusion In our 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.

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