Although aspects of long COVID are reminiscent of post-SARS and post-MERS syndromes, clinical and laboratory manifestations associated with long COVID appear to be protean, with the involvement of several organ systems. Notably, a subset of individuals who have had SARS or MERS are reported to demonstrate protracted neuropsychiatric symptoms 5, 6, 7, 8, 9, sleep abnormalities 9, persistent impairment of pulmonary function, including reductions in diffusion lung capacity ( D l CO) 8, 10, 11, 12, pulmonary fibrosis 13, myalgias 9 and functional disabilities such as reduced exercise tolerance 8, 9, 10, 11, 12. SARS-CoV-2, a novel β-coronavirus, is phylogenetically related to coronaviruses responsible for SARS and Middle East respiratory syndrome (MERS) (SARS-CoV and MERS-CoV, respectively). The US Centers for Disease Control and Prevention uses the term ‘post-COVID conditions’ as an umbrella term for the wide range of health consequences that are present ≥4 weeks after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Proposed guidelines from the National Institute for Health and Care Excellence, Scottish Intercollegiate Guidelines Network and the Royal College of General Practitioners, all in the UK, define ‘acute COVID-19’ as signs and symptoms of COVID-19 for up to 4 weeks ‘ongoing symptomatic COVID-19’ as signs and symptoms of COVID-19 present from 4 weeks to 12 weeks of infection and post-COVID-19 syndrome as signs and symptoms consistent with COVID-19 that are present for more than 12 weeks after infection and not attributable to alternative diagnoses 4. In the absence of a unifying disease definition, working constructs of long COVID have included the persistence of a constellation of symptoms for time periods varying from >4 weeks from symptom onset 2 to symptoms that last for more than 3 months after onset 3. As the world grapples with successive waves of infection fueled by the emergence of viral variants, in a subset of patients who recover, protracted disease symptoms, termed ‘long COVID’, ‘long-haul COVID’ or ‘post-COVID syndrome’, are being increasingly recognized. As of 15 November 2021, an estimated 254 million cases and 5.1 million deaths have been ascribed to COVID-19 1.
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