Secondary resistance of Helicobacter pylori to clarithromycin, metronidazole, and levofloxacin, according to year. (A) Resistance to clarithromycin, metronidazole and levofloxacin. (B) Dual clarithromycin-metronidazole resistance and simultaneous clarithromycin-metronidazole-levofloxacin resistance. Abbreviations: CLA, clarithromycin; MET, metronidazole; LEV, levofloxacin.