Molecular epidemiological investigation of an outbreak of invasive beta-haemolytic streptococcal infection in western Norway.

During a decade-long, high endemic situation with severe group A streptococcal disease in western Norway, a cluster of 16 patients with invasive streptococcal disease was hospitalized during a period of 11 weeks. A study including clinical characteristics and molecular epidemiology of the outbreak was initiated. Relevant clinical information was obtained from the medical records of the patients. Nine of the 16 patients had soft tissue infection, and seven of these had streptococcal toxic shock syndrome (STSS). Mortality, both overall and among those with STSS, was 25%. Streptococcal isolates from these patients were characterized by serogrouping and emm sequence typing. The emm amplicons were further characterized by sequence analysis and restriction fragment length polymorphism (emm RFLP) analysis. The streptococci were identified as group A streptococcus (GAS) in 11 patients and group G streptococcus (GGS) in four patients. The patients with GGS infection were older than the patients with GAS infection, and all patients infected with GGS had predisposing comorbidities. Isolates from 13 patients were available for emm gene analysis and found to belong to nine different emm types. Similar differentiation was obtained with emm RFLP in GAS. Hence, the outbreak was polyclonal. Results suggestive of horizontal gene transfer and recombination between the emm genes of GAS, group C streptococcus and GGS were found in the isolates from seven patients. Such genetic recombination events suggest a possible role in pathogenesis.