title: Influence of referral bias on the clinical characteristics of patients with Gram-negative bloodstream infection.
abstract: 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.
authors.affiliation: Department of Medicine, Division of Infectious Diseases, University of Kentucky, Lexington, KY, USA. majdi.alhasan@uky.edu
authors.forename: M N
authors.initials: MN
authors.lastname: Al-Hasan
authors.forename: J E
authors.initials: JE
authors.lastname: Eckel-Passow
authors.forename: L M
authors.initials: LM
authors.lastname: Baddour
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016470:Bacteremia / Q000453:epidemiology* / Q000382:microbiology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006090:Gram-Negative Bacteria / Q000302:isolation & purification; D016905:Gram-Negative Bacterial Infections / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D007223:Infant; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D008910:Minnesota / Q000453:epidemiology; D012017:Referral and Consultation / Q000706:statistics & numerical data