 A multicenter, randomized, double-blind, placebo-controlled phase III study to evaluate the efficacy and safety of Xolair omalizumab in Chinese patients with chronic spontaneous urticaria CSU who remain symptomatic despite antihistamine treatment The purpose of the study is to evaluate the efficacy of Xolair compared with placebo in patients with refractory CSU receiving concomitant H1 antihistamine therapy as measured by the ISS and the UAS7 instrument The primary objective is to demonstrate the superiority of omalizumab 300 mg or 150 mg administered subcutaneously every 4 weeks in patients with refractory CSU receiving concomitant H1AH therapy with respect to change from baseline in weekly itch severity score ISS7 at Week 12 compared to placebo. A total of approximately 600 patients aged 18 to 75 years old who have been diagnosed with refractory CSU and who remain symptomatic despite conventional H1AH treatment will be screened to allow 420 patients to be randomized into this study Randomization will be stratified by latent tuberculosis TB at baseline YesNo. 