Streptococcus milleri group isolates from blood cultures: consider surgical sepsis

Streptococcus milleri group bacteria (SMG) frequently are involved in purulent infections, often resulting in abscess formation with a high recurrence rate. Blood stream infections with these organisms are infrequent.

Review of epidemiologic and clinical characteristics of SMG-related bacteremia.

During a four-year period, 637 SMG-positive samples from 475 patients, including 45 positive blood cultures from 25 patients (7.1%), were identified. In one pediatric patient, the SMG was a contaminant, so 24 patients (5.1%) with 44 positive blood cultures (6.9%) were available for further evaluation. The study group consisted of 17 male and seven female patients with a median age of 56 years and a median hospital stay of 23 days (range 8-83 days). In 21 patients, monomicrobial SMG blood stream infection was found, whereas in three patients, polymicrobial infection was diagnosed (coagulase-negative staphylococci in two, Escherichia coli and Bacteroides fragilis in one). The source of the organism in the blood was intra-abdominal infection in six cases, soft tissue infection in another six cases, and cardiovascular and nervous system infection in three cases each. In the remaining cases, miscellaneous sources were identified. In 14 infected patients (58.3%), surgical interventions were performed before SMG bacteremia was diagnosed. All patients received antibiotic treatment with a median duration of 11.5 d (range 6-25 d). Five patients died, but no death was related directly to SMG infection.

Sepsis with SMG is in most cases associated with surgical infection. Source control together with directed antibiotic therapy leads to an acceptable outcome. Immunosuppression and significant co-morbidities are common in patients with this type of infection.