Clinical significance of follow-up blood culture in patients with a single Staphylococcus aureus-positive blood culture

Background: We evaluated the frequency of a positive result in follow-up blood cultures (FUBCs) and clinical outcome when FUBCs were not performed, in patients with a single Staphylococcus aureus-positive blood culture.

Methods: We analyzed blood culture results in a prospective, observational cohort of patients with S. aureus bacteraemia (SAB) at a tertiary-care hospital. All adult patients with only a single positive blood culture set from at least two blood culture sets drawn at the initial SAB episode were enrolled in the study. We analyzed FUBC results performed within 5 days after bacteraemia onset and compared the characteristics and outcomes between patients with and without FUBCs.

Results: Of 305 patients with a single S. aureus-positive blood culture, FUBCs were obtained in 274 (90%) and were positive in 15% (42/274), of whom 50% were afebrile. The rate of positivity of FUBCs was significantly higher in methicillin-resistant S. aureus (MRSA) than in methicillin-susceptible S. aureus (19% versus 9%, p = .03). In 190 patients with a single MRSA-positive blood culture, the demographic and clinical characteristics were similar between patients with and without FUBCs (167 versus 23). Although mortality was comparable between the two groups, relapse of SAB was significantly more frequent in patients in whom FUBCs were not performed (17% versus 2%, p = .008).

Conclusions: Even if a patient has a single S. aureus-positive blood culture and no fever, FUBCs should be performed to manage the infection properly and to prevent SAB relapse.