HCAI and bloodstream infection

Influence of referral bias on the clinical characteristics of patients with Gram-negative bloodstream infection

M. N. AL-HASAN^a1a2 c1, J. E. ECKEL-PASSOW^a3 and L. M. BADDOUR^a2

^a1 Department of Medicine, Division of Infectious Diseases, University of Kentucky, Lexington, KY, USA

^a2 Department of Medicine, Division of Infectious Diseases, College of Medicine, Mayo Clinic, Rochester, MN, USA

^a3 Department of Health Sciences Research, Division of Biomedical Statistics and Informatics, College of Medicine, Mayo Clinic, Rochester, MN, USA

SUMMARY

Referral bias can influence the results of studies performed at tertiary-care centres. In this study, we evaluated demographic and microbiological factors that influenced referral of patients with Gram-negative bloodstream infection (BSI). We identified 2919 and 846 unique patients with Gram-negative BSI in a referral cohort of patients treated at Mayo Clinic Hospitals and a population-based cohort of Olmsted County, Minnesota, residents between 1 January 1998 and 31 December 2007, respectively. Multivariable logistic regression analysis was used to determine factors associated with referral. Elderly patients aged ≥80 years with Gram-negative BSI were less likely to be referred than younger patients [odds ratio (OR) 0·43, 95% confidence intervals (CI) 0·30–0·62] as were females (OR 0·63, 95% CI 0·53–0·74). After adjusting for age and gender, bloodstream isolates of Escherichia coli (OR 0·50, 95% CI 0·43–0·58) and Proteus mirabilis (OR 0·49, 95% CI 0·30–0·82) were underrepresented in the referral cohort; and Pseudomonas aeruginosa (OR 2·26, 95% CI 1·70–3·06), Enterobacter cloacae (OR 2·31, 95% CI 1·53–3·66), Serratia marcescens (OR 2·34, 95% CI 1·33–4·52) and Stenotrophomonas maltophilia (OR 17·94, 95% CI 3·98–314·43) were overrepresented in the referral cohort. We demonstrated that demographic and microbiological characteristics of patients with Gram-negative BSI had an influence on referral patterns. These factors should be considered when interpreting results of investigations performed at tertiary-care centres.

(Accepted January 01 2011)

(Online publication February 01 2011)

Key Words:

• Bacteraemia;
• epidemiology;
• Gram-negative;
• population-based;
• Rochester Epidemiology Project;
• selection bias

Correspondence:

^c1 Author for correspondence: M. N. Al-Hasan, MBBS, University of Kentucky Medical Center, 800 Rose Street, Room MN 672, Lexington, KY 40536, USA. (Email: majdi.alhasan@uky.edu)