A Phase III, Multicentre, Randomised, Double-Blind Comparative Study to Evaluate the Efficacy and Safety of Ceftaroline Fosamil (600 mg every 8 hours) Versus Vancomycin Plus Aztreonam in the Treatment of Patients with Complicated Bacterial Skin and Soft Tissue Infections With Evidence of Systemic Inflammatory Response or Underlying Comorbidities