PMC3033098_01
PMC3033098_02
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.
03-0130-F1.jpg
PMC3033098_02_03-0130-F1.jpg
F1
Thirteen of these (11 residents and two staff members) subsequently proved to be carrying strains identified by PFGE analysis to be identical to the strain obtained from index case-patient 2 (Figure 1) (prevalence of colonization or infection among residents was 2.8% vs. prevalence of colonization 1.5% among staff , p=0.38 by chi-square test).
PMC3033098_03
Epidemic curve for outbreak 1. Clinical cases (black bars) of invasive GAS infection occurred at intervals of 3 to 4 months. With the occurrence of cases, acquisition of culture specimens resulted in identification of asymptomatic colonization with the outbreak strain (white bars) or unrelated strains (hatched bars) in other residents and staff. No additional clinical cases occurred after mass antibiotic treatment (M.A.T.); resident A died ( ) in July 2002; colonization of two residents with the outbreak strain was recognized 1 month later.
03-0130-F2.jpg
PMC3033098_03_03-0130-F2.jpg
F2
However, in August 2002, GAS was identified in cultures of eye drainage and wound drainage from three residents of a single wing of the facility (Figure 2).
PMC3033098_04
PMC3033098_05
Timeline for outbreak 2. Solid lines represent the time of onset and duration of illness among three cases with invasive GAS infection in outbreak 2, relative to the initiation of the outbreak investigation (date=0). Daggers ( ) denote death. Mass antibiotic treatment was started 2 days after the investigation was initiated.
03-0130-F3.jpg
PMC3033098_05_03-0130-F3.jpg
F3
This man died 36 h after admission; GAS was isolated from blood cultures taken at hospital admission (Figure 3).
Molecular epidemiology of group A streptococcal strains in outbreak 2. Pulsed-field gel electrophoresis, demonstrating relatedness of group A streptococcal isolates from facility staff and residents. Lanes 1 and 7 contain an ATCC quality control strain. Solid arrows denote identical strains from two of the three persons in whom fatal invasive group A streptococcal infection developed; the third person with invasive disease had an electrophoretically identical strain (not shown). Hollow arrows denote identical strains from persons with asymptomatic colonization with group A streptococcus. Brackets denote duplicate strains from the same person; asterisk denotes staff member.
03-0130-F4.jpg
PMC3033098_05_03-0130-F4.jpg
F4
T1 and were serum opacity factor negative (Figure 4).