Mounting evidence supports the existence of significant sequelae of coronavirus disease 2019 , the so-called post-COV-ID-19 syndrome or "long COVID", whose real incidence is unknown. Paradigmatic examples of this syndrome, whose pathogenesis and mechanisms are currently being investigated, emerge from outpatient consultations of persons who recovered from COVID-19. These patients are deeply involved psychologically and struggle to find the cause of their symptoms. They often look for other

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... COVID" patients on the web, sharing "diagnostic workup" and "therapeutic choices" that, however, are not defined at present. There is no specific clinical definition of "long-term COVID-19" agreed by the medical community. The clinical picture can be extremely variable, including non-specific symptoms, such as fatigue and lowgrade fever, or symptoms that could be related to organ damage, such as cough, breathlessness, palpitations, joint pain and abdominal pain. Residual organ injury can be detected through routine investigations. Persistent symptoms following COVID-19 include symptoms related to chronic inflammation, symptoms related to organ damage and symptoms related to hospitalization and/or isolation. Having been affected by COVID-19 may have a profound impact on patients' mental health. Moreover, persistent direct viral effects have been advocated as a possible cause of long COVID-19, including neuronal injury, post-viral post-traumatic stress disorder and mast cell activation syndrome. Also, several drugs are possibly involved in post-COVID-19 syndrome onset. At present, no defined treatment for this syndrome can be recommended. Its impact in terms of morbidity and late mortality has yet to be determined. Since studies have been limited by a relatively short follow-up of post-acute patients, well-designed, prospective, long-term follow-up studies are clearly warranted.