Sir.—The approach taken by Hayden et al1 in using a case-control study to assess the association of β-hemolytic non-group A streptococci and pharyngitis should be commended, since this design was not currently employed by authors of most reports that we previously reviewed.2 However, although the anaerobic incubation may maximize isolation of β-hemolytic non-group A streptococci, the increased isolation rate may not necessarily apply to those that are likely to be pathogenic.2
There is little evidence to implicate either β-hemolytic group B or group F streptococci as causative agents in pharyngitis.3,4 As suggested by Hayden et al, and our previous review,2 groups C and G have been incriminated in several outbreaks. Subsequent to these outbreak reports, however, basic science investigations in the genetics of group C and group G microorganisms have revealed that each of these Lancefield groups possesses more than one distinct species.2 Perhaps most important in this distinction is