Methods: We conducted a retrospective cohort study of bacteremic episodes at an academic hospital from April 1 2010 to June 30 2014. We examined clinical and microbiologic variables associated with patients undergoing repeat blood cultures, and associations with the repeat cultures being positive. A nested case control analysis was performed on a subset of patients with repeat cultures.
Results: Among 1801 index bacteremias, repeat cultures were drawn for 701 patients (38.9%), and 118 breakthrough bacteremias (6.6%) were detected. Having a repeat culture drawn was a marker of increased 30-day mortality (27.0% vs 11.2%, P<.001). Admission to a medical service (adjusted odds ratio [aOR], 2.80; 95% confidence interval [CI], 1.34-5.84), endovascular (aOR, 7.66; 95% CI, 2.30-25.48) or epidural (aOR, 26.99; 95% CI, 1.91-391.08) source, and Staphylococcus aureus bacteremia (aOR, 4.49; 95% CI, 1.88-10.73) were independently associated with breakthrough bacteremia. Escherichia coli (5.1%, P=0.006), viridans group (1.7%, P=0.035) and β-hemolytic streptococci (0%, P=0.028), and a genito-urinary source (5.9%, P=0.008) were associated with a lower likelihood of breakthrough bacteremia. Patients with breakthrough bacteremia were less likely to have undergone definitive source control within 48 hours of the index event than those with cleared bacteremia (29.7% vs 52.5%, P<.001). We identified 1031 unnecessary repeat cultures costing $22,433-$58,250.
Conclusion: Patients with S. aureus bacteremia and endovascular sources of infection are at risk of breakthrough bacteremia. Attaining source control within 48 hours of the index bacteremia may help to clear the infection. Repeat cultures after 48 hours are low yield for most Gram-negative and streptococcal bacteremias.
N. Daneman, None