A nationwide cohort study with propensity score matching

Lee and colleagues recently published the first large-scale study to investigate the association between proton pump inhibitor (PPI) use and the infectious disease caused by COVID-19.1 Using a nationwide cohort sample with propensity score matching, they concluded that short-term current—but neither long-term current nor past—PPI usage was associated with worse outcomes of COVID-19. These results deserve some comments. By decreasing the barrier effect of gastric acidity and thus promoting the survival of ingested pathogens, PPIs are a known risk factor for some enteric bacterial and virus infections.2 3 Based on the evidence for a fecal–oral transmission in COVID-19, the authors made the hypothesis that PPI use might influence the susceptibility to COVID-19. Nevertheless, criteria other than biological plausibility should be taken into account when considering retrospective observational studies, in which information is not collected with …