LJ JATON¹, TP PILLONEL², KJ JATON², ED DORY¹, GP PROD'HOM², DB BLANC², FT TISSOT³, PB BODENMANN¹, GG GREUB<sup>2

1</sup>Policlinique Médicale Universitaire, Lausanne, ²Institut de microbiologie, CHUV, Lausanne, ³Service d'infectiologie, CHUV, Lausanne

Background: Since late 2014, a high number of abscesses and boils due to Staphylococcus aureus expressing the Panton-Valentine leukocidin (PVL) were observed in Eritrean asylum seekers. We used Whole Genome Sequencing (WGS) to identify if all strains were identical or not and we checked for the presence of different kind of toxins and adhesins encoding genes; in addition, a phylogenic tree was reconstructed based on core genome single nucleotide polymorphisms (SNPs).
Methods: A total of 15 S. aureus PVL-producing strains were analyzed. Clinical and epidemiological characteristics of patients were compared to presence of adhesins, toxins and the presence of clusters of similar strains was investigated.
Results: There was 14 MSSA and 1 MRSA infections. 14/15 PVL-positive patients exhibited a skin infection (abscess, boil, adenitis or cellulitis), and 1 presented a necrotising pneumonia. Genomic sequencing showed that 8 cases (all MSSA strains) were due to MLST Sequence Type (ST) 152, 3 from ST15 and 1 each from ST 121, 72, 80 and 5. The 8 cases infected by ST152 strains included 4 Eritreans men and one Ethiopian woman, as well as two Swiss and one Portuguese patients, all in contact with African persons.
Conclusions: This work suggests that these S. aureus subtypes 152 and 15 are widespread in East Africa and that our patients have been infected by different strains of the 152 and 15 subtypes, respectively. WGS analysis showed that we are not actually facing an ongoing outbreak of infection due to PVL-producing S. aureus strains. In front of an unusual dermatological infection in African refugees, and before searching for an exotic infection (leishmaniosis, rickettsiosis or mycobacteria), clinicians must be aware that it could be a S. aureus PVL-producer. Finally, this study showed that whole genomic sequencing is a good promising tool to rapidly assess the risk of facing an epidemic.