Clinical and bacterial features of infections caused by Streptococcus milleri

The clinical and bacteriological features of 51 infections due to Streptococcus milleri observed in 43 patients over a 2-year period were reviewed. Clinical syndromes included bacteremia in 6 cases, endocarditis in 4 cases, cellulitis and subcutaneous abscesses in 8 cases, pleural empyema in 8 cases, brain abscesses in 5 cases, abdominal infections in 5 cases, and other miscellaneous infections in 15 cases. An underlying condition was associated with infection in 33/43 patients (77%). S. milleri was the only pathogen isolated in 19 patients (44%). All strains of S. milleri were susceptible to penicillin. Surgery was combined with antimicrobial therapy in 27 (63%) patients. Nine patients died during hospitalization, and death was directly related to S. milleri infection in 4 patients (9%). These results confirm that S. milleri frequently causes serious suppurative infections and that species identification is a clinically useful procedure.