A new Streptococcus group A M-29 variant isolated during a suspected common-source epidemic.

In the summer of 1988, a large epidemic of acute pharyngitis occurred in an Israeli military base. The clinical features were those of acute pharyngitis. The epidemic curve was characteristic of a common-source outbreak, possibly food-borne. Throat swabs from a sample of cases were positive for group A streptococci. Nine isolates from the epidemic were further evaluated at the local reference laboratory and serotyping showed that all were of the same strain with a distinct M protein that is a hitherto undescribed variant of M-29. We discuss the significance of unusual strains of beta-hemolytic Streptococcus appearing in food-borne outbreaks.