Yield and clinical impact of blood cultures in patients admitted to an internal medicine ward.

The purpose of this prospective observational study was to evaluate the yield and clinical impact of blood cultures in a 78-bed Internal Medicine ward of a medium-sized Italian acute care hospital. During a two-month study period, 154 (mean age: 75.2 ++ 12.2 years; 94 males) out of 620 (24.8%) hospitalized patients underwent 174 blood cultures and were enrolled in the study. The rate of true-positive cultures was 11.5% (20/174) and the rate of false-positive (contaminants) was 5.7% (10/174). A total of 23 microorganisms (5 multidrug resistant strains), most frequently Escherichia coli (n = 10), Klebsiella pneumoniae (n = 3) and Staphylococcus aureus (n = 3), were isolated. The positivity rate was significantly higher in patients with urinary tract infection (31%) and abdomen infection (26.1%) than in patients with pneumonia (4.9%; p<0.01). Although the positivity rate in patients exposed to antibiotics was lower than in those not exposed, the difference was not statistically significant. Therapy changes due to blood culture positivity were observed in 7.1% of the patients overall. In-hospital death was observed in nine of the 136 patients with negative blood cultures (6.6%) and in none of the 18 patients with positive blood cultures. These results indicate that the yield and clinical impact of blood cultures is quite low in patients admitted to an Internal Medicine ward and suggest the need to improve the adequacy of the indications to perform the test.