Background: Streptococci as a group remain an important cause of infective endocarditis (IE). With improvements in diagnostic technology, causative pathogens are now more easily identified to the species level. The purpose of this study was to describe the distribution of streptococcal groups causing IE.
Methods: Adult patients with definite IE (Duke Criteria) admitted to the hospital from July 1, 2007 to December 31, 2013, were identified from the Cleveland Clinic Infective Endocarditis Registry. Blood culture, valve culture, and valve sequencing (University of Washington) results were examined to describe the distribution of streptococcal species. The streptococci were grouped according to the Bergey’s Manual of Systematic Bacteriology.
Results: A total of 255 patients had ≥1 episodes of streptococcal IE during the study period of which 69% (176) were native valve IE. The mean (± SD) patient age was 58 ± 14 years; 75% (190) were men. The overall distribution of streptococci was: 77% viridans (n= 197); 16% pyogenic (42); 5% nutritionally variant (13), and 1% anaerobic (3). Sixty-one (31%) of the viridans group streptococci were not identified further. The distribution of the remaining 136 viridans group streptococci was as follows: mitis group 78 (57%), bovis group 22 (16%), mutans group 20 (15%), anginosus group 14 (10%), and salivarius group 2 (1%). Of the 42 pyogenic streptococci, 32 (75%) were S. agalactiae and 8 (19%) were S. dysgalactiae. Of the nutritionally variant streptococci 8 (62%) were Granulicatella spp., the remaining 5 (38%) were Abiotrophia spp.
Conclusion: Mitis group streptococci are by far the most common streptococci causing IE. Pyogenic streptococci cause about 16% of all cases of streptococcal IE, with S. agalactiae accounting for almost 80% of IE caused by pyogenic streptococci.