Abstract: diagnostics Article Association between Vitamin D Status and Secondary Infections in Patients with Severe COVID-19 Admitted in the Intensive Care Unit of a Tertiary-Level Hospital in Turkey Lutfiye Karcioglu Batur 1, * and Suna Koç 2 1 2 * Citation: Batur, L.K.; Koç, S. Association between Vitamin D Status and Secondary Infections in Patients with Severe COVID-19 Admitted in the Intensive Care Unit of a Tertiary-Level Hospital in Turkey. Diagnostics 2023, 13, 59. https:// doi.org/10.3390/diagnostics13010059 Academic Editor: Aw Tar-Choon Department of Molecular Biology and Genetics, Faculty of Engineering and Natural Sciences, Biruni University, Istanbul 34010, Turkey Department of Anesthesiology and Reanimation, Medical Faculty, Biruni University, Istanbul 34010, Turkey Correspondence: lbatur@biruni.edu.tr; Tel.: +90-444-82-76 (ext. 2133) Abstract: There are several studies showing that the vitamin D status can determine risk of COVID19 infections, severity and mortality from coronavirus disease 2019 (COVID-19). However, the association between vitamin D (25(OH)D) and secondary infections in the prognosis of COVID-19 patients has not been reported yet. The aim was to investigate whether the vitamin D status affects the rates of secondary infections in patients with severe COVID-19 hospitalized in the intensive care unit (ICU) of a tertiary-level hospital in Turkey. The data of 194 patients with diagnosis of severe COVID-19 who were admitted to the ICU from March 2020 to June 2021 and older than 18 years were evaluated in this retrospective study. The patients were divided into two groups according to total serum 25(OH)D level as normal group (≥20 ng/mL) and low group (<20 ng/mL). The 25(OH)D level was low in 118 (60.8%) and normal in 76 (39.2%) patients. The mean age of the low group was significantly higher than that of the normal group (67.02 ± 14.47 vs. 61.70 ± 14.38; p = 0.013). The systolic and diastolic blood pressure as well as the Glasgow coma scale score of the low group were significantly lower than that of the normal group (p = 0.004, 0.002 and 0.001, respectively). The intubation rate and APACHE (Acute Physiology and Chronic Health Evaluation) score of the low group was significantly higher than that of the normal group (p = 0.001). The platelets number and blood pH decreased, and the neutrophil/lymphocyte ratio, procalcitonin, lactate, urea, creatinine and lactate dehydrogenase concentrations increased significantly in the low group (p < 0.05). The mortality rate was 79.7% in the low group and 22.4% in the normal group (p < 0.001). Microbiological growth was observed in 68.6% of the normal group and 52.6% of the normal group (p = 0.025). The number of cultures with resistant bacteria was significantly higher in the low group (25.9%) than that in the normal group (17.5%) (p = 0.035). The severe COVID-19 patients hospitalized with vitamin D deficiency may have increased risks of poor prognosis and mortality due to secondary infections in the ICU. Keywords: vitamin D status; COVID-19; Intensive Care Unit; secondary infections Received: 25 October 2022 Revised: 16 December 2022 Accepted: 17 December 2022 Published: 26 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).