Actinomyces in the Bloodstream: A Pathogen or Passenger?

Actinomyces, a genus of branching, gram-positive rods, is part of the normal flora in the oral cavity, genitourinary tract, and gastrointestinal tract. Despite their frequent isolation, advancements in molecular identification through matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and 16S rRNA sequencing have complicated clinical interpretations, especially regarding their relevance when detected in blood cultures. Limited studies exist on Actinomyces bacteremia, leaving its clinical significance and treatment necessity largely uncertain. This study aimed to assess the clinical relevance of Actinomyces bacteremia and its impact on treatment decisions, with the goal of potentially minimizing unnecessary antibiotic use.

This cross-sectional, retrospective study was conducted using data on patients admitted to the University of Louisville Healthcare network between June 2022 and May 2023. Positive blood cultures for any species of Actinomyces were included, identifying 18 cases for analysis. Patient data was collected through chart reviews focusing on clinical presentations, treatment initiation, imaging, and follow-up outcomes for at least one month post-bacteremia. Data was kept confidential and securely stored, following ethical protocols.

The mean age of patients was 58.5 years (SD = 21.26), with 66.67% male patients. Treatment was administered to only 11.11% (n=2) of patients, highlighting a predominant trend of non-treatment (n=16, 88.89%). Follow-up data for 17 cases indicated a mean duration of 6.58 months (SD = 6.15), ranging from 1 to 26 months. Mortality was observed in 33.33% of cases, although some deaths were attributed to unrelated causes.

Actinomyces bacteremia may often be clinically insignificant, as the majority of patients in this study did not receive treatment and showed varied outcomes. These findings suggest the need for a cautious approach in initiating prolonged antibiotic therapy for Actinomyces bacteremia.