Due to the lack of any epidemiologic link between case-patients and the population mixing that had occurred at the holiday party, swab cultures were collected on all facility residents and all available staff members. Epidemic control measures were introduced and included restriction of new admissions to the facility and reinforcement of infection control practices. Based on the rapidity of events, the apparent high case-fatality rate, and recent experience with the failure of targeted culturing and treatment (as described in outbreak 1), a decision was made to initiate mass antibiotic treatment for all facility residents and staff. After that decision, but before mass antibiotic treatment could be initiated, an 89-year-old male resident was admitted to the hospital with "congestive heart failure." Gram stain of sputum indicated gram-positive cocci in chains. This man died 36 h after admission; GAS was isolated from blood cultures taken at hospital admission (Figure 3).
Mass antibiotic treatment was initiated approximately 48 h after the start of the investigation, with azithromycin, 250 mg orally each day, administered for 5 days to residents and to staff who wished to be treated at the facility. Staff who wished to receive antibiotic treatment from their personal physicians were permitted to do so. Subsequently, GAS was isolated from nasal and pharyngeal cultures of two staff members and five residents of the facility. GAS was also isolated from a wound culture from a facility resident.
All colonized residents were negative for GAS on repeat cultures, 4 weeks after receiving antibiotics. One staff member remained culture positive 2 weeks after completing a course of cephalexin provided by her personal physician; she received two additional courses of beta-lactam antibiotics and was documented to be culture negative for GAS 4 weeks after she completed the second antibiotic course.
PFGE performed on the three GAS strains from case-patients and the seven strains from colonized residents and staff showed that four colonized persons had isolates identical to those from the deceased case-patients; all were serotype M1 T1 and were serum opacity factor negative (Figure 4). The remaining three isolates represented two distinct strains unrelated to the outbreak strain. The proportion of residents colonized or infected with the outbreak strain was significantly higher than the proportion of staff colonized (4.7% vs. 0.7%, p=0.03 by chi-square test).