S960 Influenza Infection Increases Risk of GERD and Its Subtypes Before and After the COVID-19 Pandemic

Introduction: The risk and temporal patterns of gastroesophageal reflux disease (GERD) following an influenza infection remain poorly characterized. This study aimed to evaluate the incidence and risk of GERD and its subtypes, including erosive esophagitis (EE) and non-erosive reflux disease (NERD), in adults with influenza, comparing periods before and after the COVID-19 pandemic. Methods: This retrospective cohort study analyzed data from the TriNetX database, including adult patients (≥18 years) diagnosed with influenza between January 1, 2016, and December 31, 2023, allowing up to 12 months of follow-up through January 1, 2025. Patients with prior GERD or concurrent viral infections, including COVID-19, were excluded. Two cohorts were studied: pre-pandemic (2016-2019) and post-pandemic (2020-2023). Propensity score matching (1:1) was performed based on demographics and GERD risk factors. Kaplan-Meier analysis and Cox proportional hazards models assessed GERD incidence at 3, 6, and 12 months post-influenza. Subgroup analyses evaluated GERD subtypes (EE, NERD), influenza types (A, B), and sex. Results: Initial cohorts comprised 553,795 influenza patients and 4,531,438 controls pre-pandemic, and 1,500,582 influenza patients and 4,734,921 controls post-pandemic. After matching, final analysis included 511,938 influenza patients versus 4,697,247 controls pre-pandemic, and 1,385,486 influenza patients versus 4,331,201 controls post-pandemic. Influenza infection significantly increased GERD risk overall (odds ratio [OR] 1.32; 95% confidence interval [CI] 1.30-1.34; P < 0.001). GERD risk was slightly higher post-pandemic (OR 1.35; 95% CI 1.33-1.37; P < 0.001) compared to pre-pandemic (OR 1.26; 95% CI 1.23-1.29; P < 0.001), and remained consistent at 3, 6, and 12 months post-infection. Influenza significantly increased risks for both GERD subtypes: EE (OR 1.34; 95% CI 1.31-1.37; P < 0.001) and NERD (OR 1.28; 95% CI 1.25-1.31; P < 0.001). Women showed slightly higher GERD risk than men (EE: OR 1.37 vs 1.31; NERD: OR 1.31 vs 1.24; all P < 0.001). Both influenza A and B were significantly associated with increased GERD (A: OR 1.31; 95% CI 1.29-1.33, B: OR 1.28; 95% CI 1.24-1.32), EE (A: OR 1.33; B: OR 1.30), and NERD (A: OR 1.27; B: OR 1.25). Conclusion: Influenza infection significantly increases the risk of GERD and its subtypes, emphasizing the need for clinical vigilance.