 There is clinical equipoise about the question of whether antibiotic prophylaxis should be given for a short period or an extended period of time as reflected by inconsistencies in major guidelines, current practices at Canadian centers, and as concluded in the three systematic reviews. There also is clinical equipoise on whether the addition of vancomycin to routine cefazolin prophylaxis can further reduce s-SSI rates. A short duration of combined antimicrobial prophylaxis can reduce side effects of exposure to antimicrobials such as infections with C. difficile or emergence of resistance, but may also reduce the incidence of s-SSIs. The objective of the eventual full scale study is to determine whether adding vancomycin to cefazolin can reduce SSIs as well as whether short-term prophylaxis is as effective as long-term prophylaxis. The rationale to conduct the proposed pilot study is to assess the feasibility to conduct this factorial cluster randomized cross-over trial, the adherence to the study protocol at each pilot site, the length of time to fill out the case report forms, and to get reliable estimates of event rates for sample size calculation for the main study 