Time to blood culture positivity in Staphylococcus aureus bacteremia: Association with 30-day mortality

Summary 

Objectives

Time to blood culture positivity (TTP) has been suggested as a prognostic factor for adverse clinical outcome. This study describes the relationship between TTP and clinical outcome in all patients with Staphylococcus aureus bacteremia (SAB) in a large Canadian health region.

Methods

We performed a retrospective study of all first episodes of SAB occurring in the former Calgary Health Region (population ∼1.2 million) from July 1, 2006 to December 31, 2008.

Results

Overall, 684 cases of SAB were evaluated. The median TTP was 16 h and 31/684 (5%) cases had TTP at >48 h. Time to positivity was shorter for methicillin-susceptible Staphylococcus aureus compared with methicillin-resistant S. aureus (MRSA) and for endovascular sources compared with other sources of infection. The overall 30-day case-fatality rate was 18% (124/684). Patients with delayed TTP (>48 h) suffered the highest case-fatality rate (39%) compared to those with earlier TTP (17%; P = 0.002). Multivariable logistic regression modeling showed that age, nosocomial acquisition, MRSA, focus of infection, liver disease, and TTP ≤12 and >48 h were associated with 30-day mortality.

Conclusion

Although uncommon, delayed TTP may be associated with increased mortality. Empiric antimicrobial therapy should continue beyond 48 h in patients at high risk for SAB.

Keywords: Staphylococcus aureus, Bacteremia, Time to positivity