Nonlinear Relationship Between Myeloperoxidase Levels and Helicobacter pylori Infection Risk in Chinese Adults: A Population-Based Cross-Sectional Study

<b>Objectives:</b> This study investigates the nonlinear association between myeloperoxidase (MPO) levels and <i>Helicobacter pylori</i> (<i>H. pylori</i>) infection risk in Chinese adults, evaluating potential modifiers and clinical implications for infection prevention. <b>Methods:</b> An analysis was conducted on cross-sectional data from 15,180 adults who underwent routine health examinations between January and December 2021. <i>H. pylori</i> infection was diagnosed using the 14C-urea breath test with a threshold of disintegrations per minute (DPM) ≥ 100. ELISA was used to measure plasma MPO levels. Nonlinear associations were assessed through logistic regression, restricted cubic splines, threshold effect analysis, and subgroup interactions. <b>Results:</b> The study identified a U-shaped correlation between MPO levels and the risk of <i>H. pylori</i> infection. Compared to the middle tertile (T2: 20.6-31 ng/mL), participants in the lowest (T1: ≤20.6 ng/mL; OR = 1.36, 95% CI: 1.24-1.49) and highest tertiles (T3: ≥31 ng/mL; OR = 1.12, 1.02-1.22) exhibited elevated infection risk after full adjustment (<i>p</i> < 0.001). DPM levels were notably elevated in T1 (β = 37.1, 26.66-47.57) and T3 (β = 19.27, 8.81-29.72) relative to T2 (<i>p</i> < 0.0001). RCS-based threshold analysis identified a nonlinear inflection at 24.0 ng/mL of MPO, where each additional 1 ng/mL of MPO below this threshold was associated with a reduced infection risk (OR = 0.959, 95% CI: 0.947-0.971), whereas levels above increased the risk (OR = 1.004, 95% CI: 1.002-1.007). This pattern aligned with <i>H. pylori</i> breath test values, which mirrored the U-shaped trend across MPO tertiles. Subgroup analyses revealed uniform associations between MPO and <i>H. pylori</i> infection risk/DPM across various factors such as age, sex, BMI, and metabolic comorbidities, with all interaction <i>p</i>-values exceeding 0.05. <b>Conclusions:</b> MPO levels exhibit a robust U-shaped association with <i>H. pylori</i> infection risk, independent of anthropometric and metabolic confounders. Monitoring MPO may aid in identifying individuals at bidirectional infection risk, suggesting novel insights into the inflammation-infection interplay. The study's cross-sectional design limits the ability to establish causal relationships, necessitating further longitudinal research to validate these findings and elucidate their clinical implications.