Figure 1. Molecular epidemiology of group A streptococcus (GAS) strains in outbreak. Pulsed field gel electrophoresis, demonstrating relatedness of group A streptococcal isolates from an person with clinical illness from GAS, a person with chronic colonization with GAS, and asymptomatically colonized facility staff and residents. Lanes 1 and 15 contain an ATCC quality control strain. Lane 14 contains an isolate from another nursing facility, unrelated to outbreak 1. The isolate in lane 2 (large solid arrow) was obtained from index case-patient 2 in January 2001. The isolate in lane 7 (large hollow arrow) was obtained from a person with chronic GAS colonization (resident A) in May 2001. Small solid arrows denote electrophoretically identical GAS strains from other persons with asymptomatic colonization with group A streptococcus in May 2001. Asterisk denotes staff member.