Boarding school outbreak of group A streptococcal pharyngitis.

In an outbreak of pharyngitis caused by group A beta-haemolytic Streptococcus pyogenes in a boarding school of 261 pupils and 45 staff, 14 cases and 16 asymptomatic carriers were identified in pupils and one case was a member of staff. One symptomatic pupil had negative swabs. Two pupils had recurrent S. pyogenes pharyngitis before the outbreak. The attack rate was significantly greater in two dormitories than in the other seven. Swabs were taken from all staff and pupils, and the outbreak was controlled by treating all carriers and cases. Environmental factors enhancing airborne transmission were considered. The two dormitories with the most cases were poorly ventilated.