Surveillance for Hospital Outbreaks of Invasive Group A Streptococcal Infections in Ontario, Canada, 1992 to 2000

Abstract

Streptococcus pyogenes can cause severe disease in the individual patient and dramatic hospital outbreaks. To describe the epidemiology of hospital outbreaks of invasive group A streptococcal infection in order to understand the potential benefit of proposed outbreak investigation and management strategies. Prospective, population-based surveillance. Short-term care hospitals in Ontario, Canada. Persons with a positive culture for group A streptococcus from a normally sterile site between 1 January 1992 and 31 December 2000. Laboratory-based surveillance identified patients with nosocomial invasive group A streptococcal infection. Epidemiologic and microbiological investigations were used to detect transmission. Of 2351 cases of invasive group A streptococcal disease, 291 (12%) were hospital acquired. Twenty-nine (10%) nosocomial cases occurred as part of 20 outbreaks. Seventy percent (14 of 20) of outbreaks involved nonsurgical, nonobstetric patients. Community-acquired cases initiated 25% of outbreaks; most were cases of necrotizing fasciitis in patients admitted to the intensive care unit. Outbreaks were small (median, 2 cases [range, 2 to 10 cases]) and short (median duration, 6 days [range, 0 to 30 days]). The median time between the first 2 cases was 4.5 days. The most common mode of propagation was patient-to-patient transmission. A staff carrier was the primary mode of transmission in 2 (10%) outbreaks, but 1 or more health care workers were colonized with the outbreak strain in 6 of 18 (33%) other outbreaks. Some outbreaks with 1 case of invasive disease may have been missed; advice provided to participating hospitals may have reduced the number and size of outbreaks. Practices to prevent hospital transmission of group A streptococci should include isolation of patients admitted to the intensive care unit with necrotizing fasciitis, investigation after a single nosocomial case, and emphasis on identifying and treating health care worker carriers on surgical and obstetric services and patient reservoirs on other wards.