Coronavirus Pathology is frequently associated with both diabetes mellitus and metabolic syndrome. In particular, results of observational studies and meta-analyzes configure diabetes as one of the main risk factors for the development of complications and unfavorable course of SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome), the syndromes caused respectively by SARS- VOC coronavirus and MERS-COV coronavirus. The available data confirm this association also in the clinical picture of the infection supported by SARS-COV 2 (COVID-19). In the epidemic outbreak that erupted at the beginning of 2020 in the Lombardy Region, about two thirds of the patients who died from COVID-19 were affected by diabetes mellitus. COVID-19 occurs in 70% of cases with an inflammatory pathology of the airways that can be fed by a cytokine storm and result in severe respiratory failure (10% cases) and death (5%). At the moment, the mainly involved pathophysiological molecular mechanisms are not clearly defined. It has been hypothesized that the transmembrane glycoprotein type II CD26, known for the enzyme activity Dipeptilpeptidase 4 exerted by its extracellular domain, may play a fundamental role in this process. In addition, it is considerably expressed at the parenchyma and lung interstitium level and carries out both systemic and paracrine enzymatic activity, modulating the activity of various proinflammatory cytokines, growth factors and vasoactive peptides at the level of the deep respiratory tract. The pulmonary parenchyma and the interstitium express significantly the Dipeptilpeptidase 4 protein, which in the Middle East Respiratory Syndrome favors the entry of the virus into the cells, thus allowing the virus to replicate within the cells and thus spread throughout the cell inside the organism. Dipeptilpeptidase 4 regulates the function of bioactive peptides and above all of cytokines, vasoactive peptides and chemokines present at the level of the mesothelium, of the deep respiratory tract (alveolar epithelium and alveolar bronchus), of endothelial and immune cells triggering the inflammatory storm. In line with this evidence, it has been hypothesized that acute respiratory disease from Coronavirus may depend on the massive localization of Dipeptilpeptidase 4 in lung tissue. Furthermore, the involvement of Dipeptilpeptidase 4 in other chronic respiratory diseases has been demonstrated. Starting from these observations we hypothesized that the selective blockade of Dipeptilpeptidase 4 can favorably modulate the pulmonary inflammatory response in the subject affected by COVID-19. Among the drugs that selectively block Dipeptilpeptidase 4, the one with greater affinity precisely for Dipeptilpeptidase 4 is Sitagliptin.

An observational, retrospective-case control, multi-center study is proposed to evaluate any effects of Sitagliptin on clinical, laboratory and instrumental parameters in the course of hospitalization for COVID-19. The data will be extracted anonymously from the computerized medical records commonly used in clinical practice by the centers involved in the study. The evaluation will be performed by comparing the parameters of COVID-19 positive diabetic patients treated with Sitagliptin with those of a group of COVID-19 positive diabetic patients not treated with Sitagliptin. All diabetic subjects treated with Sitagliptin (100 mg / day, 50 mg / day or 25 mg / day) and all diabetic subjects not treated with Sitagliptin, eligible for inclusion / exclusion criteria, will be included in the analysis.

The clinical data of patients that will be collected anonymously during hospitalization will include: smoking habit, remote medical history aimed at assessing the presence of comorbidities (atrial fibrillation, heart failure, hypertension, arterial hypertension, chronic obstructive pulmonary disease, other lung disease, chronic renal failure, decay cognitive, Parkinson's disease, autoimmune diseases), pharmacological history (treatment introduced during hospitalization for COVID-19, respiratory failure or other complications; use of ACE-inhibitors, sartans, calcium channel blockers, diuretics, antiarrhythmics, beta blockers, anti-aggregants, anticoagulants, neuroleptics ). Anthropometric parameters including blood pressure measurement and BMI will also be collected.

For all patients, the following data will be collected at the baseline (first data available upon entry into the hospitalization regime) and upon discharge:

• Clinical picture and symptoms (presence of cough, body temperature, respiratory rate, need for ventilatory support, duration of ventilatory support in days, duration of oxygen therapy in day, duration of hospitalization in Intensive Care Unit in days, total length of stay in days, blood gas parameters, PaO2 / FiO2 ratio, oxygen saturation by pulse oximeter)
• Routine blood chemistry tests performed in hospitalization (e.g. glycemia, reactive protein C, blood count with formula, erythrocyte sedimentation rate, blood gas analysis, LDH, inflammation indices).
• Instrumental exams (chest x-ray)
• glycated hemoglobin
• Serum creatinine and Estimated Glomerular Filtration Rate (estimated with CKD-EPI)
• Presence of specific comorbidities for diabetes
• Average daily blood sugar levels (from capillary blood)

Inclusion Criteria:

• Diagnosis of type 2 diabetes, according to ADA 2020 criteria
• Diagnosis of COVID-19 (positive SARS-COV2 RNA buffer) with pneumonia, with or without an increase in inflammation indexes, with or without respiratory failure

Exclusion Criteria:

• Pregnancy
• Type 1 diabetes
• Presence of other acute infections in place
• Presence of serious diseases or conditions that make the patient unsuitable for the study

The anonymous data of diabetic patients hospitalized for COVID19 in the hospitals participating in the study will be collected