Milleri group streptococcus--a stepchild in the viridans family

The purpose of this investigation was to provide a comprehensive review of the pathogenic role and spectrum of disease of milleri group streptococci, with special attention to bloodstream invasion and to possible differential roles among the three species. All consecutive isolates of milleri group streptococci from any anatomic source, during a 37-month period, in a tertiary care teaching hospital in Tel-Aviv, Israel, were thoroughly investigated. Identification to the species level was performed by an automated system.Streptococcus anginosus constituted 82% of the 245 patient-unique isolates from hospitalized patients. All nonurinary isolates were involved in pyogenic infections mostly originating from the gastrointestinal tract, with bacteremia in 28 cases. The 71 urinary isolates represented either urinary tract infection or nonsignificant bacteriuria. No specific association could be detected between species and the infection site, except for a higher relative representation of Streptococcus constellatus in bacteremia. Milleri group streptococci are common in clinical practice and play a different pathogenic role to other viridans streptococci. Due to their invariable association with pyogenic processes, their presence in blood warrants immediate focus identification. In addition, they have a previously unappreciated clinical niche concerning urinary tract infection. The identification of viridans streptococci to the species level is of paramount clinical significance.