Bacteremia involving the "Streptococcus milleri" group: analysis of 19 cases

Area of Science:

• Medical Microbiology
• Infectious Diseases
• Clinical Epidemiology

Background:

• The Streptococcus milleri group consists of bacteria commonly found in the human oral and gastrointestinal flora.
• Infections caused by these bacteria can manifest in various body sites, often leading to abscess formation.
• Bloodstream infections (BSIs) due to Streptococcus milleri group are relatively uncommon but can be associated with significant morbidity and mortality.

Purpose of the Study:

• To determine the incidence, clinical characteristics, and outcomes of bloodstream infections caused by the Streptococcus milleri group at a university hospital.
• To identify risk factors and common sites of infection associated with these BSIs.
• To analyze the antimicrobial susceptibility patterns of the isolated strains.

Main Methods:

• A retrospective study was conducted over a 3-year period at the University Hospital of Maastricht.
• Patient data, including demographics, underlying conditions, clinical presentation, microbiological findings, and outcomes, were collected and analyzed.
• Infecting Streptococcus milleri group strains were identified to the species level and tested for antimicrobial susceptibility.

Main Results:

• The incidence of Streptococcus milleri group BSIs was 0.33 per 1,000 admissions.
• Malignancy was the most common underlying disease, and local trauma to the mucosal barrier was a significant risk factor.
• The abdominal and thoracic cavities were the most frequent associated sites of infection. Streptococcus anginosus was the predominant species, and abscess formation occurred in 47.3% of cases.
• Mortality was high, with 26.3% of patients dying.

Conclusions:

• Bloodstream infections with the Streptococcus milleri group, particularly Streptococcus anginosus, are associated with significant mortality and a high rate of abscess formation.
• Underlying conditions like malignancy and local trauma are important risk factors.
• Effective management requires prompt recognition, source control, and appropriate antimicrobial therapy, although isolates were generally sensitive to most antibiotics.