Asia Pacific Consensus states that levofloxacin-based triple therapy as an alternative second-line therapy after Helicobacter pylori (H. pylori) eradication failure when bismuth salts are not available. The investigators compare the efficacies of 10-day levofloxacin-based sequential therapy and 10-day triple therapy in the treatment for patients after failure of standard triple therapy and to determine what clinical and bacterial factors influencing the efficacy of salvage regimens.