Not performing follow-up blood cultures may be significantly associated with the relapse of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, according to a study recently published in Infectious Diseases.

S aureus bacteremia (SAB) is a common serious community- and healthcare-associated infection worldwide. The overall mortality rate of SAB remains at 30% even with improvements from the antibiotic era. Given the high mortality rate and rarity of S aureus contamination of blood cultures, it has been recommended that even a single S aureus-positive blood culture be considered clinically significant. Follow-up blood cultures drawn at 2- to 4-day intervals until negative are necessary in SAB to help determine treatment duration and to predict the complication of bacteremia.

However, only 1 previous study has evaluated the clinical significance of a single S aureus blood culture from multiple blood cultures, and no studies have explored the clinical significance and positivity rate of follow-up blood cultures in a single S aureus-positive blood culture. Therefore, researchers evaluated the frequency of a positive result in follow-up blood cultures and clinical outcome when such cultures were not performed, in patients with a single S aureus-positive blood culture.

In total, 305 patients with a single S aureus-positive blood culture from at least 2 blood culture sets drawn at the initial SAB episode were included from an observational cohort at a tertiary-care hospital. Follow-up blood culture results performed within 5 days after bacteremia onset were analyzed and compared with the characteristics and outcomes of patients with and without follow-up blood cultures.

Of the 305 patients included, follow-up blood cultures were obtained in 274 (90%) of patients. In total, there were 42 (15%) patients with positive follow-up blood cultures, of whom 50% were afebrile. Compared with methicillin-susceptible S aureus (9%), the follow-up blood culture positivity rate was significantly higher in MRSA (19%; P =.03). In total, there were 190 patients with a single MRSA-positive blood culture; of these patients, the demographic and clinical characteristics were similar between patients with (n=167) and without (n=23) follow-up blood cultures. Mortality was similar for the 2 groups. SAB relapse was significantly more frequent in patients in whom follow-up blood cultures were not performed (17% vs 2%; P =.008).

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Overall, the study authors concluded, “Even if a patient has a single S. aureus-positive blood culture and no fever, [follow-up blood cultures] should be performed to manage the infection properly and to prevent SAB relapse.”

Reference

Kim T, Lee SC, Kim MJ, et al. Clinical significance of follow-up blood culture in patients with a single Staphylococcus aureus-positive blood culture [published online December 13, 2019]. Infect Dis. doi: 10.1080/23744235.2019.1701198