| influence of referral bias on the clinical characteristics of patients with gram-negative bloodstream infection. | summaryreferral 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, respec ... | 2011 | 21281552 |