Increasing severity of invasive group A streptococcal disease in Australia: clinical and molecular epidemiological features and identification of a new virulent M-nontypeable clone.

We conducted a 12-year review of all cases of group A streptococcal (GAS) bacteremia that were seen at Royal Children's Hospital in Melbourne, Australia, from 1982 through 1993. Forty-two cases were identified. There was a trend towards increased incidence of infections, as well as a clear increase in their severity, during the study period; more previously healthy children were affected during the last 6 years of the study (80% of cases) than during the first 6 years (47% of cases), and more complications occurred during the latter period than during the former (40% vs. 20%, respectively, with an 88% complication rate over the last 12 months). Seventy-four GAS isolates (41 invasive, 23 noninvasive, and 10 indeterminate) were analyzed. An M type 1 clone that was positive for the pyrogenic exotoxin A gene (speA) and that has been found to cause invasive disease in the Northern Hemisphere was most frequent among invasive isolates. Molecular typing also identified a genetically distinct strain that was virulent, mucoid, and M nontypable. Invasive GAS disease in Melbourne has become increasingly aggressive. Newer typing methods should be used in conjunction with traditional serotyping in order to maintain epidemiological surveillance of virulent strains.