Molecular epidemiology of a Streptococcus pyogenes related nosocomial outbreak in a burn unit

Background: Group A Streptococcal (GAS) infections have increased infrequency and severity worldwide. During April 1996, a nosocomial outbreak associated to GAS infections affected seven patients admitted to a pediactric burn unit. The causative organism was likely disseminated from the source patient to another child in the emerging room before he was transferred to the burn unit. Patients developed burn infections or invasive disease. One of them died due to a toxic shock syndrome and 3 other lost their skin grafts. Perineal and nasal microbiological surveillance of 42 related health care workers identified only one of them as carrier of S pyogenes. Aim: 76 report a molecular analysis of an apparently clonal outbreak. Material and methods: The available isolates were analyzed by molecular methods including random amplified polymorphic DNA analysis (RAPD) with 4 different primers, Sma-I pulsed field gel electrophoresis (PFGE) analysis, and speA, speB and speC detection by polymerase chain reaction (PCR). Results: Two phylogenetically distant and sequentially isolated bacterial groups were identified either by RAPD analysis with selected primers or by Smal-PFGE analysis. The first group involved isolates identified in two patients that included the lethal case. The second bacterial group comprised 5 clinical isolates and the perineal and nasal isolates obtained from a health case worker. Only strains belonging to the first group harbored the speA gene and were associated with invasive disease. The second group, could be split further in two subgroups according to their speB profile. Conclusions: RAPD analysis with selected primers can reproduce the PFGE-discriminating ability on the epidemiological analysis of GAS infections.