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

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.

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

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 < or =12 and >48 h were associated with 30-day mortality.

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.