Characteristics of Patients with Persistent COVID-19 Symptoms and Unscheduled Return Visits to a Centre for COVID-19 Evaluation

<b>Background:</b> This retrospective study aimed to evaluate the characteristics of patients with long COVID syndrome. <b>Methods:</b> This study included 457 adults who had at least one persistent symptom after COVID-19 infection. <b>Results:</b> The median time interval between the last SARS-CoV-2 infection and emergency room presentation was 3 months. Older patients had comorbidities (61.7 vs. 44.9 years, <i>p</i> < 0.0001), moderate or severe forms of COVID-19 (61.2 vs. 50.9 years, <i>p</i> < 0.0001), and respiratory symptoms (56.1 vs. 52.0 years, <i>p</i> = 0.0027). Non-vaccinated patients were older than vaccinated patients (56.0 vs. 51.5 years, <i>p</i> = 0.0008) and had residual lung abnormalities following COVID-19 infection (51.5% vs. 36.8%, <i>p</i> < 0.003). The time interval between the last SARS-CoV-2 infection and the hospital evaluation was shorter for vaccinated patients (3.2 vs. 3.9 months, <i>p</i> < 0.0001) and those with mild forms (3.3 vs. 4.12 months, <i>p</i> = 0.0001) versus non-vaccinated individuals. After the last SARS-CoV-2 infection, 107 patients developed impaired fasting glucose, impaired glucose tolerance, or diabetes mellitus, being patients with already known chronic diseases (<i>p</i> = 0.0002), or hypertension (<i>p</i> = 0.001). <b>Conclusions:</b> Our study pointed out the heterogeneity of symptoms following COVID-19, and they are associated with age, vaccination status, or severity of SARS-CoV-2 infection.