Microbiologia Médica e Diagnóstico

The Association between Time to Positivity and Staphylococcus Aureus Bacteremia in a Geriatric Population

Abstract

Maillart E, Karmali R, Miendje Deyi VY, Mascart G and Cherifi S

 Background: Time to Positivity (TTP) of blood cultures is defined as the time elapsed between the start of incubation and the automated alert signal indicating growth in the culture bottle. This study evaluates the TTP of blood cultures in patients with Staphylococcus aureus Bacteremia (SAB) and assesses the relationship between TTP and mortality,
Methods: We performed a retrospective study involving adults who had SAB between May 2007 and May 2010 in a tertiary hospital. TTP was defined as the time between onset of incubation and growth detection using an automated blood culture system.
Results: A total of 167 SAB were evaluated. Patient’s median age was 72 years (range, 18-95 years). The median TTP was 13.6 h (range, 3.6-95.2 h). Attributable mortality rate (27.5%) was not related to the TTP (P=0.558) nor to the comorbidities. Age >60 years was the only independent predictor of attributable mortality (P<0.001). Univariate analysis revealed a significantly shorter TTP in persistent bacteremia, endovascular source of infection, catheter-related infection and in community-acquired SAB. A TTP >11.3 h had a negative predictive value of 96.4% for endocarditis. TTP was not related to methicillin susceptibility nor resistance of Staphylococcus aureus (P=0.934).
Conclusion: In our elderly population, shorter TTP was significantly associated with a central source of infection and a persistent SAB. In addition for the first time, community-acquired SAB was associated with a shorter TTP. TTP  may contribute to a better management of SAB by facilitating clinical decisions, especially in endocarditis