Streptococci and aerococci associated with systemic infection in man

Abstract

A collection of 820 isolates of streptococci and aerococci from human blood or internal organs was classified by means of a set of cultural and biochemical tests. Of these, 719 (712 streptococci and 7 aerococci) were from patients believed to be suffering from a systemic infection: endocarditis 317; a purulent lesion in an internal organ ("purulent disease") 152; bacteriaemia 250. The endocarditis streptococci included members of all recognisable taxa, but only certain of these were common: Streptococcus sanguis, 16-4%; dextran-positive and usually mannitol-fermenting strains of S. bovis (S. bovis I), 15-1%; S. mutans, 14-2%; S. mitior, 13-2%. Streptococci of the "alpha-haemolytic" taxa (S. sanguis, S. mitior and related strains) formed only 44-8% of the total. When the percentage frequency of streptococcal taxa among the endocarditis and "non-endocarditis" isolates was compared, the dextran-forming taxa (S. mutans, S. bovis I, S. sanguis, and dextran-positive streptococci otherwise resembling S. mitior) all had higher "endocarditis : non-endocarditis" ratios than did any of the non-dextran-producing taxa. Endocarditis increased in frequency with age, and showed an excess of males over females up to the age of 65 years. In young patients (less than 35 years), "alpha-haemolytic" streptococci predominated; with increasing age, the proportion of other streptococci increased progressively but the absolute numbers of isolations of "alpha-haemolytic" streptococci did not fall. Infections with S. mutans were prominent in the age-group 35-54 years and with S. bovis I at ages greater than or equal to 55 years. A history of previous heart disease was more often obtained in endocarditis due to "alpha-haemolytic" streptococci than in other streptococcal endocarditis. The streptococcus most often isolated from purulent lesions in internal organs was S. milleri (29-3%). It was associated with brain abscess, meningitis, pleural empyema and a variety of intra-abdominal abscesses. The only common predisposing factor in endocarditis was previous heart damage. In other systemic streptococcal diseases, other general or local predisposing causes could be observed, mainly in infections with the "pyogenic" groupable streptococci, the enterococci and S. milleri.