Genetic relatedness of coagulase negative staphylococci in sternal wound colonisation and sternal wound infection after open heart surgery

Abstract number: 1134_02_167

Balmelli C., Hysenai R., Senn G., Spiess Pangrazzi M., Schmid E., Turina M., Ruef C.

Objective:

Coagulase-negative staphylococci (CoNS) are frequently isolated in sternal wound infections (SWI) after open heart surgery. Our study had two principal aims. First, to establish the source and route of transmission of staphylococci found in SWI and sternal wound colonization during interventions under laminar flow ventilation (LVF). Second, to assess the source of strains found in the ultra clean area (UCA) and to define the role of airborne transmission.

Methods:

Prospective evaluation of 50 patients undergoing elective open heart surgery. Swabs of noses and hands of HCW involved in patient care. Swabs of noses and sternal skin of patients before interventions. Three air samples done during each intervention in the vicinity of the surgical site. Genotyping of all 2413 cultured isolates of CoNS using pulsed field gel electrophoresis (PFGE).

Results:

Two out of 50 patients developed SWI, one infection was caused by CoNS and needed surgical revision, the second was caused by coryneform bacteria. PFGE showed that the CoNS originated from the hands of a supporting staff member (SSM) who shaved the patient just before intervention. Another CoNS strain was found in the same wound during revision, and was traced to another SSM who took care of the patient just before reintervention.

Five out 50 patients had intraoperative sternal wound colonization with CoNS. None of these CoNS genotypes were observed among isolates from patients, HCW or from the air. Most air samples showed <10 CFU/m³. 17/216 (8%) of CoNS isolates from the air could be traced to HCW or patients, among which 50% originated from the non-scrubbed team.

Conclusions:

Analysing the origin of colonization or infection in 6 patients with CoNS isolated from the operative site, the bacteria could only be traced in one patient who developed an infection. Transmission most probably occurred by direct contact. The low level of bacterial contamination in the UCA together with the lack of correlation of genotypes between isolates found in the UCA and in the wounds suggest that airborne transmission does not play a major role in the development of SWI. More than 90% of staphylococci found in air samples were not traceable to any investigated sources. Most probably, they originated from non swabbed parts of the HCW's bodies. Since 50% of the traceable isolates from the UCA originated from non scrubbed team members, protection of the operative site by LFV appears to be suboptimal.