Incidence and pathogenicity of Arcanobacterium haemolyticum during a 2-year study in Ottawa.

Arcanobacterium haemolyticum has been described as a rare cause of systemic invasive disease and is occasionally isolated from throat swabs. We describe a 2-year study of the incidence and clinical features of A. haemolyticus infection in a pediatric and adolescent population. A total of 11,620 throat swabs were examined for A. haemolyticum with use of a locally developed selective medium. Controls (2,241) were healthy students who were recruited from a separate study. A. haemolyticum was isolated from 42 patients, with the maximum incidence in the 15 to 18-year-old age group; in this subset the incidence was 2.5%. There were no isolates of A. haemolyticum found in the healthy controls, and the difference in incidence between patients and controls in the 15 to 18-year-old age group was highly significant (P < .01). Approximately half of the patients infected with A. haemolyticum had a rash. In 5 patients, A. haemolyticum was associated with a positive monospot test. The organism was highly susceptible to erythromycin and less susceptible to penicillin. The evidence from this study suggests that A. haemolyticum may be a pathogen with maximum incidence in the 15 to 18-year-old age group.