Suboptimal Vitamin D Status Is Associated with Salmonella Infection and Elevated C-Reactive Protein in Hospitalized Children with Acute Gastroenteritis: A Retrospective Cohort Study

<b>Background:</b> Vitamin D contributes to intestinal barrier integrity and innate immune regulation, but its role in susceptibility to <i>Salmonella</i> infection and systemic inflammation in hospitalized pediatric patients with acute gastroenteritis (AGE) remains unclear. <b>Methods:</b> We retrospectively analyzed 70 pediatric patients hospitalized with AGE, examining the associations of admission 25(OH)D levels with culture-confirmed <i>Salmonella</i> infection and <i>C</i>-reactive protein (CRP). Multivariable logistic and linear regression models were adjusted for age and sex. Vitamin D status was classified as sufficient (≥30 ng/mL), suboptimal (<30 ng/mL), or deficient (<20 ng/mL). <b>Results:</b> The median age of the 70 included patients was 3.0 years (IQR: 1.5-6.0, range: 1.0-17 years), and 55.7% were male. Suboptimal vitamin D status was present in 64.3% of patients and was associated with higher median CRP levels (3.84 vs. 1.42 mg/dL, <i>p</i> = 0.025) and a greater prevalence of <i>Salmonella</i> infection (48.9% vs. 24.0%, <i>p</i> = 0.047). In multivariable analysis, suboptimal 25(OH)D levels independently marginally predicted an increased odds of <i>Salmonella</i> infection (adjusted odds ratio 3.11, 95% CI 1.00-9.67; <i>p</i> = 0.051). Serum 25(OH)D levels were inversely associated with natural log-transformed CRP (<i>p</i> = 0.026), with each 1 ng/mL increase corresponding to an estimated 5% reduction in CRP. Furthermore, vitamin D deficiency (<20 ng/mL) was associated with a 3.5-fold increase in CRP compared to levels ≥ 20 ng/mL (<i>p</i> = 0.012). <b>Conclusions:</b> Suboptimal vitamin D status (<30 ng/mL) may be associated with increased susceptibility to <i>Salmonella</i> gastroenteritis, while deficiency (<20 ng/mL) correlates with exacerbated inflammatory burden in hospitalized pediatric patients. These findings suggest a threshold-dependent effect of vitamin D on both mucosal defense and systemic inflammation. Prospective trials are warranted to evaluate the therapeutic potential of vitamin D supplementation in this population.