Gatta L, et al. - Experts examined the prevalence of primary resistance to clarithromycin, metronidazole and levofloxacin along with the effectiveness of sequential therapy on resistant strains for Helicobacter pylori infection. They also sought to estimate the minimum number of subjects to enrol for assessing the effectiveness of an eradication regimen in patients harbouring resistant strains. A rise was reported in the H. pylori-primary resistance and served as the most critical factor affecting effectiveness. Findings unveiled that the sequential therapy eradicated 83% of strains resistant to clarithromycin and metronidazole. In patients harbouring resistant strains, reliable estimates of the effectiveness of a given regimen could be achieved only through the analysis of a large number of strains.