A CA-MRSA strain with decreased vancomycin susceptibility as a cause of serious invasive infection in an immunocompetent adolescent

Abstract number: 1733_1095

Tronci M., Parisi G., Pantosti A., Monaco M., Valentini P.

Obiectives: CA-MRSA are primarily associated with skin and soft tissue infection although they can also cause more serious infections such as necrotising pneumonia and septicaemia. This report describes a severe invasive infection in a immunocompetent adolescent with isolation of an CA-MRSA strain with decreased susceptibility to vancomycin.

Methods: Blood and CSF cultures were obtained from a 16-year old Italian boy admitted to the Paediatric Emergency room with a temperature of 40.5°C, stiff neck, headache and vomiting. The patient was previously healthy with no recent hospitalisation story; he played football and had a purulent skin lesion in the back. An empiric therapy with a 3rd generation cefalosporin was started. The identification and susceptibility tests were performed by PHOENIX instrument. Susceptibilities were confirmed by E-test. The presence of the Panton-Valentine Leucocidin (PVL) toxin genes lukS-PV-lukF-PV was determined by PCR. The structural type of the Staphylococcal chromosomal cassette mec (SCCmec) was performed by multiplex PCR. Multi-locus sequence typing (MLST) was performed to characterise the clonal group.

Results: Blood and CSF cultures grew an MRSA. In vitro susceptibility tests showed that both the isolates from blood and from CSF were resistant to oxacillin, and were sensitive to gentamycin, kanamycin, erythromycin, clindamycin, rifampicin, tetracycline, ciprofloxacin, chloramphenicol and linezolid. MIC to vancomycin was 4 mg/mL. The isolates contained SCCmec type IV and were positive for PVL. By MLST the isolates were found to belong to the European clone. The patient was transferred to another hospital where vancomycin was started. On the third day, his condition deteriorated and he was admitted to the ICU for respiratory distress and hypoxaemia. The chest X-ray revealed infiltrates and the CT scan showed severe necrotising pneumonia. The antimicrobial regimen was switched to linezolid, rifampicin and teicoplanin. His conditions improved and he was discharged after four weeks.

Conclusions: To our knowledge this is the first case of an invasive infection due to a CA-MRSA strain with decreased susceptibility to vancomycin. We emphasize the importance of an early laboratory diagnosis for an appropriate and successful therapy. An epidemiological surveillance system is needed to characterise and monitor CA-MRSA infections and to understand how MRSA are transmitted in the community.