The goal of this pragmatic, multi-centre factorial cluster randomized cross-over trial is to assess the efficacy of a combination of cefazolin plus vancomycin compared to cefazolin monotherapy, as well as a comparison of short versus long-term prophylaxis with four study arms: 1) cefazolin short-term, 2) cefazolin long-term, 3) cefazolin plus vancomycin short-term and 4) cefazolin plus vancomycin long-term.

Although antibiotic prophylaxis is considered the cornerstone of prevention for sternal surgical site infections (s-SSIs), the most effective antimicrobial regimen and optimal duration remain unclear. There is a pressing need to determine how best to prevent sternal surgical site infections and at the same time reduce adverse events from unnecessary antibiotic exposure. Currently, due to the lack of evidence, unproven approaches prevail and adherence to guidelines is poor. Rigorous randomized controlled trials data are needed for improved patient care.

A factorial cluster randomized cross-over trial, a design not used previously in this field, will address these gaps. To date, we have successfully enrolled close to 6,000 eligible patients in the vanguard study, and have shown that the trial as planned is feasible and operationally highly cost-effective.

Inclusion Criteria:

Adult patients (≥18 years of age) undergoing open-heart surgery (i.e. sternotomy, including minimally-invasive surgical techniques through mini-sternotomies)

Exclusion Criteria:

1. On systemic antibiotics or with an active bacterial infection at the time of surgery
2. Previously enrolled in this trial
3. Known to be colonized with methicillin-resistant staphylococcus aureus (MRSA). Where it is unethical to not administer glycopeptides.
4. Beta-lactam or vancomycin allergy precluding the use of cefazolin or vancomycin, respectively
5. Participation in other studies that may interfere with this trial.
6. Patients undergoing cardiac transplant