title: Using a longitudinal model to estimate the effect of methicillin-resistant Staphylococcus aureus infection on length of stay in an intensive care unit.
abstract: Health-care-associated methicillin-resistant Staphylococcus aureus (MRSA) infection may cause increased hospital stay, or sometimes death. Quantifying this effect is complicated because the exposure is time dependent: infection may prolong hospital stay, while longer stays increase infection risk. In this paper, the authors overcome these problems by using a multinomial longitudinal model to estimate the daily probability of death and discharge. They then extend the basic model to estimate how the effect of MRSA infection varies over time and to quantify number of excess days in the intensive care unit due to infection. They found that infection decreased the relative risk of discharge (relative risk ratio = 0.68, 95% credible interval: 0.54, 0.82). Infection on the first day of admission resulted in a mean extra stay of 0.3 days (95% credible interval: 0.1, 0.5) for a patient with an Acute Physiology and Chronic Health Evaluation II score of 10 and 1.2 days (95% credible interval: 0.5, 2.0) for a patient with a score of 30. The decrease in the relative risk of discharge remained fairly constant with day of MRSA infection but was slightly stronger closer to the start of infection. Results confirm the importance of MRSA infection in increasing stay in an intensive care unit but suggest that previous work may have systematically overestimated the effect size.
authors.affiliation: School of Public Health and Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland, Australia.
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Barnett
authors.forename: Rahul
authors.initials: R
authors.lastname: Batra
authors.forename: Nicholas
authors.initials: N
authors.lastname: Graves
authors.forename: Jonathan
authors.initials: J
authors.lastname: Edgeworth
authors.forename: Julie
authors.initials: J
authors.lastname: Robotham
authors.forename: Ben
authors.initials: B
authors.lastname: Cooper
mesh_terms: D000328:Adult; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007362:Intensive Care Units / Q000706:statistics & numerical data*; D007902:Length of Stay / Q000706:statistics & numerical data*; D008137:Longitudinal Studies; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus; D008875:Middle Aged; D012307:Risk Factors; D012737:Sex Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000401:mortality; D013997:Time Factors