The Role of the Selective Throat Culture for Beta Hemolytic Streptococci in the Diagnosis of Acute Pharyngitis

Abstract

In the screening of acute respiratory disease, and particularly in the diagnosis of simple sore throat, the relatively easy and inexpensive procedure of direct inoculation of sheep blood agar plates and their subsequent gross examination for beta hemolytic colonies after incubation for 18 to 24 hours at 37C, constitutes a method for excluding, with reasonable assurance, the bacterial etiology of most pharyngeal infections. The presence of beta hemolytic streptococci do not necessarily prove the streptococcal etiology of a pharyngeal infection, inasmuch as the strain isolated (1) may belong to serologic groups other than group A; (2) may be group A organisms that are of relatively low virulence; (3) may be group A organisms that are present in relatively few numbers; and (4) may be group A organisms which produce an infection too mild to provoke an immune response, and thus are of little risk in initiating rheumatic fever. Unfortunately, the clinician faced with a patient who has a sore throat and a positive culture for beta hemolytic streptococci must make his decision to treat or not to treat acute respiratory disease on the basis of this information alone. It would be well to provide him with the most economical, practical, and effective means for distinguishing between viral and streptococcal pharyngitis that is currently available, namely, the throat culture made directly on sheep blood agar plates.