Mass antibiotic treatment for group A streptococcus outbreaks in two long-term care facilities

Abstract

Outbreaks of invasive infections caused by group A β-hemolytic streptococcus (GAS) may occur in long-term care settings and are associated with a high case-fatality rate in debilitated adults. Targeted antibiotic treatment only to residents and staff known to be at specific risk of GAS may be an ineffective outbreak control measure. We describe two institutional outbreaks in which mass antibiotic treatment was used as a control measure. In the first instance, mass treatment was used after targeted antibiotic treatment was not successful. In the second instance, mass treatment was used to control a rapidly evolving outbreak with a high case-fatality rate. Although no further clinical cases were seen after the introduction of mass antibiotic treatment, persistence of the outbreak strain was documented in one institution >1 year after cases had ceased. Strain persistence was associated with the presence of a chronically colonized resident and poor infection control practices.

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.

Figure 2

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.

Figure 3

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.

Figure 4

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.