Use of surveillance data to calculate the sample size and the statistical power of randomized clinical trials testing Staphylococcus aureus vaccine efficacy in orthopedic surgery.

ABSTRACT

BACKGROUND: Patients undergoing primary total hip arthroplasty (THA) would be a worthy population for anti-staphylococcal vaccines. The objective is to assess sample size for significant vaccine efficacy (VE) in a randomized clinical trial (RCT). METHODS: Data from a surveillance network of surgical site infection in France between 2008 and 2011 were used. The outcome was S. aureus SSI (SASSI) within 30 days after surgery. Statistical power was estimated by simulations repeated for theoretical VE ranging from 20% to 100% and for sample sizes from 250 to 8000 individuals per arm. RESULTS: 18,688 patients undergoing THA were included; 66 (0.35%) SASSI occurred. For a 1% SASSI rate, the sample size would be at least 1316 patients per arm to detect significant VE of 80% with 80% power. CONCLUSION: Simulations with real-life data from surveillance of hospital acquired infections allow estimation of power for RCT and sample size to reach the required power.