A cluster of ecthyma outbreaks caused by a single clone of invasive and highly infective Streptococcus pyogenes

Background. Ecthyma is an invasive, ulcerated skin infection. Four ecthyma outbreaks occurred in different infantry units in the Israeli Defense Force from October 2004 through February 2005. Morbidity attack rates in the first 3 outbreaks were 89% (49 of 55 soldiers), 73% (32 of 44), and 82% (37 of 45). In the fourth outbreak, in which early intervention (antimicrobial treatment and improvement of hygiene) was applied, the attack rate was 25% (10 of 40 soldiers). In the first outbreak cluster, 4 soldiers experienced poststreptococcal glomerulone- phritis, and 5 cases of systemic sequelae were recorded (1 case of severe septic shock, 3 cases of pneumonia, and 1 case of septic olecranon bursitis). Methods. Streptococcus pyogenes and Staphylococcus aureus were isolated from ecthyma sores, oropharynx, and anterior nares of affected and unaffected soldiers involved in all 4 outbreaks. Results. Although the S. aureus isolates had different genomic profiles, >90% of S. pyogenes isolates were identified as belonging to a single clone, emm type 81, T type 8. Epidemiological investigation revealed that the hygiene levels of the soldiers and their living conditions were probably the most important cause for the difference in attack rates, wound severity, and systemic sequelae found between and within the units. Conclusions. Our study demonstrates the possible ramifications of the combination of a virulent and highly infective S. pyogenes strain and poor living conditions, and it emphasizes the importance of early intervention in such conditions.