Attributable Length of Stay, Mortality Risk, and Costs of Bacterial Health Care-Associated Infections in Australia: A Retrospective Case-cohort Study

Abstract

Background: Unbiased estimates of the health and economic impacts of health care-associated infections (HAIs) are scarce and focus largely on patients with bloodstream infections (BSIs). We sought to estimate the hospital length of stay (LOS), mortality rate, and costs of HAIs and the differential effects on patients with an antimicrobial-resistant infection.

Methods: We conducted a multisite, retrospective case-cohort of all acute-care hospital admissions with a positive culture of 1 of the 5 organisms of interest (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, or Enterococcus faecium) from 1 January 2012 through 30 December 2016. Data linkage was used to generate a data set of statewide hospital admissions and pathology data. Patients with bloodstream, urinary, or respiratory tract infections were included in the analysis and matched to a sample of uninfected patients. We used multistate survival models to generate LOS, and logistic regression to derive mortality estimates.

Results: We matched 20 390 cases to 75 635 uninfected control patients. The overall incidence of infections due to the 5 studied organisms was 116.9 cases per 100 000 patient days, with E. coli urinary tract infections (UTIs) contributing the largest proportion (51 cases per 100 000 patient days). The impact of a UTI on LOS was moderate across the 5 studied pathogens. Resistance significantly increased LOS for patients with third-generation cephalosporin-resistant K. pneumoniae BSIs (extra 4.6 days) and methicillin-resistant S. aureus BSIs (extra 2.9 days). Consequently, the health-care costs of these infections were higher, compared to corresponding drug-sensitive strains.

Conclusions: The health burden remains highest for BSIs; however, UTIs and respiratory tract infections contributed most to the health-care system expenditure.

Keywords: antimicrobial resistance; cost; hospital-associated infections; length of stay; mortality.

Figure 1.

Multi-state model used to determine the length of stay. The alphas (α) represent the transition hazards. Abbreviations: A, patients discharged alive; D, patients who died in hospital; I, infected patients; U, uninfected patients.

Figure 2.

Infection-attributable LOS for health care–associated infections in the (A) bloodstream, (B) urinary tract, and (C) respiratory tract, Queensland, 2012–2016. Abbreviations: 3GC, third-generation cephalosporin; CI, confidence interval; E. coli, Escherichia coli; E. faecium, Enterococcus faecium; K. pneumoniae, Klebsiella pneumoniae; LOS, length of stay; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-sensitive S. aureus; P. aeruginosa, Pseudomonas aeruginosa; S. aureus, Staphylococcus aureus; VRE, vancomycin-resistant E. faecium; VSE, vancomycin-sensitive E. faecium.

Figure 3.

Infection-attributable mortality for patients with health care–associated infections in the (A) bloodstream, (B) urinary tract, and (C) respiratory tract, Queensland, 2012–2016. Odds ratios presented were for the reference category: that is, an uninfected female patient with age equal to the mean age in the cohort who was admitted in 2012 to a Principal Referral Hospital located in a metropolitan setting and had no comorbidities. For the resistant versus susceptible comparison, the time to infection covariate was taken to be the average time to infection of infected patients in the data set. Dots represent the point estimate. Triangles represent the change between Resistant and Sensitive groups. Bold indicates significant results where the odds ratio was above 1. Abbreviations: 3GC, third-generation cephalosporin; CI, confidence interval; E. coli, Escherichia coli; E. faecium, Enterococcus faecium; K. pneumoniae, Klebsiella pneumoniae; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-sensitive S. aureus; P. aeruginosa, Pseudomonas aeruginosa; S. aureus, Staphylococcus aureus; VRE, vancomycin-resistant E. faecium; VSE, vancomycin-sensitive E. faecium.

Figure 4.

Infection-attributable annual costs for health care–associated infections in the (A) bloodstream, (B) urinary tract, and (C) respiratory tract, Queensland, 2012–2016. Abbreviations: 3GC, third-generation cephalosporin; CI, confidence interval; E. coli, Escherichia coli; E. faecium, Enterococcus faecium; K. pneumoniae, Klebsiella pneumoniae; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-sensitive S. aureus; P. aeruginosa, Pseudomonas aeruginosa; S. aureus, Staphylococcus aureus; USD, United States dollar; VRE, vancomycin-resistant E. faecium; VSE, vancomycin-sensitive E. faecium.