A matter of time: impact of time to first follow-up blood cultures in patients with candidemia and Staphylococcus aureus bacteremia from a retrospective cohort

Guidelines recommend performing follow-up blood cultures (FUBCs) in patients with Staphylococcus aureus bacteraemia (SAB) and candidemia due to increased mortality in persistent infections, but their impact on length of stay (LOS), length of treatment (LOT), and time to the first negative FUBCs has been less described. Patients admitted to our Institution with SAB or candidemia were included. Correlation between time to first FUBCs and outcomes were performed using Spearman rank test. We performed survival analysis using a multivariate Cox regression model. Patients dying before 72 h were excluded to limit survival bias. The study included 217 patients with SAB and 138 patients with candidemia. The correlation between time to first FUBCs and LOS was statistically significant for SAB (rho =0,19; p value 0,05), but not for candidemia (rho= 0,37; p value 0,08). Time to first FUBCs correlated significantly with LOT in both groups (SAB rho =0,31; p value =0,02; candidemia rho=0,37; p value <0,001) and first negative FUBCs (SAB rho =0,88; p value <0,001; candidemia rho=0,66; p value <0,001). In multivariate Cox regression model, FUBCs within 48 hours (HR 0,26 (0,07 – 0,91), p value 0,04) were associated with improved survival for SAB, while not performing FUBCs (HR 3,31 (1,04 – 10,60), p value 0,02) affected survival in patients with candidemia. These results show that delaying FUBCs was associated with a deleterious impact on LOT, LOS, and culture clearance. Furthermore, our findings highlight the importance of timely follow-up blood cultures within the integrated care of these infections, together with source control, effective antimicrobial therapy, and infectious disease consultation to improve survival.