Epidemiologic evidence for Lancefield group C beta-hemolytic streptococci as a cause of exudative pharyngitis in college students

Abstract

The isolation rates of strains of group C beta-hemolytic streptococci from throat swab cultures of patients with exudative pharyngitis, the common cold, and healthy controls were compared. By using a cohort study design in a college health service, patients with exudative pharyngitis were retrospectively identified by description of tonsillar exudate on chart review. Patients with rhinoviral infection were prospectively identified during a common cold study. Healthy controls were prospectively recruited from patients presenting with noninfectious conditions. Isolation of Lancefield group A and C beta-hemolytic streptococci from throat cultures was used as an outcome measurement. A total of 265 students (62% female; average age 20.2 years) with exudative pharyngitis were identified. A total of 75 students (60% female; average age, 21.7 years) from a common cold study with rhinoviral infection were identified. A total of 162 students (53% female; average age, 22.6 years) were recruited as healthy controls. Group A beta-hemolytic streptococci were isolated from 5% of patients with pharyngitis but none of those with rhinovirus (P = 0.045) and none of the controls (P = 0.007). Group C Streptococcus dysglactiae subsp. equisimilis was isolated from 11% of patients with pharyngitis but none of those with rhinovirus (P = 0.006) and 2% of controls (P = 0.001). Lancefield group C Streptococcus anginosus was isolated from 8% of patients with pharyngitis but 3% of those with rhinovirus (P = 0.18) and 1% of controls (P = 0.006). Heavier growth of colonies on the primary culture plate was observed for patients from whom S. equisimilis and group A beta-hemolytic streptococci were isolated. Lancefield group C beta-hemolytic streptococci appear to be associated with exudative pharyngitis in college students.