Acute pharyngitis is one of the most common conditions encountered in office practice, accounting for 12 million ambulatory visits in the United States annually . While group A streptococcus is an important treatable infection, it accounts for a minority (approximately 5 to 15 percent) of adults presenting with pharyngitis . Despite this, a majority of patients with pharyngitis receive presumptive antibiotic therapy. One report estimates that 60 percent (95% CI 57-63 percent) of adults seen in a US clinic in 2010 for a complaint of sore throat received an antibiotic prescription, with a trend toward prescribing broader spectrum antibiotics (azithromycin) rather than narrow spectrum antibiotics (eg, penicillin) . Overtreatment of acute pharyngitis is a major cause of inappropriate antibiotic use, which can be avoided by a systematic approach to evaluation and treatment .
The etiology, general approach to, and evaluation of acute pharyngitis in adults will be reviewed here. The treatment and complications of group A streptococcal pharyngitis and symptomatic management of pharyngitis are discussed separately. (See "Treatment and prevention of streptococcal tonsillopharyngitis" and "Symptomatic treatment of acute pharyngitis in adults".)
Infectious causes — Multiple pathogens can cause pharyngitis (table 1) . Although viruses are believed to cause most cases of pharyngitis, the relative frequency of particular pathogens in adults is uncertain, since most studies are old and include both children and adults [6-8]. Identification of a particular microorganism, by culture or rapid antigen detection, does not prove causation of the pharyngitis since many organisms colonize the upper respiratory tract without causing disease.
Group A streptococcus (GAS) — The most important treatable agent is group A streptococcus (GAS). Approximately 5 to 15 percent of sore throats in adults yield positive cultures for GAS .
Clinical features of GAS include the sudden onset of sore throat, tonsillar exudate, tender cervical adenitis, and fever. Cough and significant rhinorrhea are usually absent. The Centor criteria (exudate, cervical adenopathy, fever history, and lack of cough) provide a clinical prediction rule with reasonable negative predictive value in excluding streptococcal pharyngitis [9,10]. (See 'Centor criteria' below.)