Vitamin D Levels and Uropathogen Distribution in Urinary Tract Infections: A Six-Year Retrospective Study from Cyprus

Background and Objectives: Urinary tract infections (UTIs) represent one of the most frequently encountered bacterial infections in clinical practice. Although vitamin D (vit D) is recognised for its immunomodulatory properties, its relationship with the spectrum of uropathogens remains unclear. This study investigated the distribution of UTI-causing pathogens in relation to serum vit D status and demographic variables including age, sex, season, and year of presentation at a tertiary hospital in the Eastern Mediterranean. Materials and Methods: A retrospective cross-sectional analysis was conducted on 942 adult patients with culture-confirmed UTIs at a university hospital in Cyprus between January 2019 and December 2024. Serum 25-hydroxyvitamin D [25(OH)D] levels were classified as deficient (≤20 ng/mL), insufficient (20-29.9 ng/mL), or sufficient (≥30 ng/mL) according to Turkish Endocrinology Society (TEMD) guidelines. Pathogen distribution was correlated with vit D category, sex, age group, season, and year using chi-square analysis and multivariable logistic regression. Timing of urine culture collection (at admission vs. more than 48 h after admission), catheter use, upper vs. lower urinary tract classification, and comorbidity data were recorded for each patient. Results: Escherichia coli was the most frequently isolated uropathogen (48.83%), followed by Klebsiella pneumoniae (18.79%) and Enterococcus faecalis (11.89%). No statistically significant association was found between vit D level and uropathogen type (p = 0.504). Infections were more prevalent in females (70.49%) and in patients aged over 70 years (56.26%). Vit D deficiency was present in 47.98% of the cohort. Catheter-derived specimens accounted for 35.1% of cultures. Upper tract infection was diagnosed in 233 patients (24.7%) and lower tract infection in 709 patients (75.3%). The most frequent comorbidities were hypertension (48.4%), diabetes mellitus (33.1%), and chronic kidney disease (21.0%); on multivariable analysis, diabetes mellitus (adjusted OR = 1.4) and chronic kidney disease (adjusted OR = 1.6) were independently associated with K. pneumoniae infection. In vit D-deficient patients, K. pneumoniae infection risk was significantly higher during winter in unadjusted analysis (OR = 1.8; 95% CI: 1.3-2.5) and remained elevated after multivariable adjustment (aOR = 1.6; 95% CI: 1.1-2.3). Vit D levels showed significant seasonal variation (p < 0.001), with lower values in winter (18.6 ng/mL) and higher values in summer (28.4 ng/mL). Conclusions: On multivariable analysis, no statistically significant association was found between vit D level and uropathogen species overall (χ² = 13.291; p = 0.504); a seasonal interaction was observed between vit D deficiency and Klebsiella infections in winter. UTI risk was highest in elderly and female patients. These findings point to the need for considering seasonal and dietary factors in UTI management and call for prospective investigation.