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J Thorac Cardiovasc Surg 2007;134:670-676
© 2007 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

Staphylococcus aureus poststernotomy mediastinitis: Description of two distinct acquisition pathways with different potential preventive approaches

^a Unit of Infectious Diseases, University Hospital "12 de Octubre," Madrid, Spain
^b Department of Microbiology, University Hospital "12 de Octubre," Madrid, Spain
^c Department of Cardiothoracic Surgery, University Hospital "12 de Octubre," Madrid, Spain.

Partially presented at the 46th Interscience Congress on Antimicrobial Agents and Chemotherapy, San Francisco, Calif, Oct 27-30, 2006. Oral communication K-0625.

Received for publication February 5, 2007; revisions received March 27, 2007; accepted for publication April 11, 2007.

^_* Address for reprints: Rafael San Juan, Unidad de Enfermedades Infecciosas. Hospital Universitario "12 de Octubre," Edificio Maternidad, planta 6°, Avenida de Andalucía km 5,400, 28041 Madrid, Spain. (Email: rafasjg{at}yahoo.es).

Objective: Determining the acquisition routes of infection is crucial to designing specific preventive approaches against Staphylococcus aureus poststernotomy mediastinitis.

Methods: From 2002 to 2004, a nasal sample was obtained from patients before cardiac surgery. We collected clinical and microbiologic data of all episodes of S aureus poststernotomy mediastinitis. A case–control study (3:1) was performed to confirm the role of previous preoperative nasal colonization by S aureus as a risk factor for S aureus poststernotomy mediastinitis. Pulsed field gel electrophoresis molecular analysis of nasal and surgical site S aureus isolates was performed to analyze their relatedness in each patient with poststernotomy mediastinitis and with other patients of the study cohort.

Results: S aureus nasal cultures were positive in 228 (15.9%) of 1432 patients: methicillin-susceptible S aureus in 222 (15.5%) and meticillin-resistant S aureus in 6 (0.4%). S aureus poststernotomy mediastinitis was diagnosed in 17 (1.2%) of 1432 patients: 9 (3.95%) of 228 in colonized patients versus 8 (0.66%) of 1204 in noncolonized patients (P < .0001). Seven of 9 patients (1.2%) with methicillin-susceptible S aureus had an identical isolate by pulsed field gel electrophoresis in preoperative nasal and surgical-site cultures, but no clonal relatedness was shown among the isolates from these 9 patients. None of the 8 patients with methicillin-resistant S aureus poststernotomy mediastinitis had an identical isolate by pulsed field gel electrophoresis in preoperative nasal and surgical-site cultures, and the same clone of methicillin-resistant S aureus was responsible for all these cases.

Conclusions: Nasal colonization often precedes methicillin-resistant S aureus poststernotomy mediastinitis, which suggests that decontamination is adequate for preventing methicillin-resistant S aureus poststernotomy mediastinitis, whereas hospital infection control measures seem to be the major factor for preventing methicillin-resistant S aureus poststernotomy mediastinitis.