Accurate diagnosis of group A streptococcal pharyngitis and appropriate antimicrobial therapy are important, particularly to prevent nonsuppurative sequelae such as rheumatic fever. Most episodes of sore throat, however, are caused by viral agents. Clinical findings cannot reliably differentiate streptococcal from viral pharyngitis and most physicians tend to overestimate the probability of a streptococcal infection based on history and physical examination alone. Therefore, diagnosis should be based on results of a throat culture or an antigen-detection test with throat culture backup. Presumptively starting therapy pending results of a culture is discouraged because treatment often continues despite a negative test result. Other bacterial causes of pharyngitis are uncommon and often can be diagnosed based on nonpharyngeal findings. Penicillin remains the drug of choice for streptococcal pharyngitis because of its effectiveness, relatively narrow spectrum, and low cost. No group A streptococci are resistant to β-lactam antibiotics. High rates of resistance to macrolides has been documented in several areas; in Finland, decreased national rates of macrolide use led to a decline in the proportion of macrolide-resistant group A streptococci.
Serological identification of group A streptococci from throat scrapings before culture