and was later followed by other terms, such as post-COVID-19 condition, post-acute sequelae of SARS-CoV-2 infection, and post-COVID syndrome.
This condition can affect different organs and body systems, with a wide range of signs and symptoms reported. Given the magnitude of the sequelae of SARS-CoV-2 infection, it is essential to agree upon the nomenclature and definition to assess its incidence, subtypes, and severity. This process cannot be left to agencies, health-care providers, or researchers alone, but requires extensive consultation, notably including the people affected.
Another issue is that the severity, features, and urgency of long COVID—as highlighted by patients—are not fully addressed within the framework of other terms and definitions. Long COVID remains the patient-preferred term.
Most published research uses persistent symptoms, measured at variable time points after an acute episode or proven infection, as a primary outcome,
and call this outcome one of the above-mentioned names, which is another source of heterogeneity. Analysis of the condition’s development over time is crucial.
), the UK National Institute for Health and Care Excellence,
and the US Centers for Disease Control and Prevention (table).
Notably, long COVID is still widely used by researchers as a very broad term covering persistent signs and symptoms that continue or develop after acute SARS-CoV-2 infection for any period of time, whereas some other terms have much more stringent definitions.
TableCommonly used terminology in the research of COVID-19 sequelae
NICE=National Institute for Health and Care Excellence (UK).
A recent analysis showed that clinical manifestations described in more than 80 cohorts 3 weeks or more after acute SARS-CoV-2 infection resulted in 287 unique clinical findings in accordance with the Human Phenotype Ontology, which is a widely used standard for exchange and analysis of phenotypic abnormalities in human disease.
It is difficult to accurately establish the time when acute COVID-19 ends, and data regarding the duration of long-term viral persistence are lacking, although long COVID is not necessarily caused by viral persistence. The health consequences of various SARS-CoV-2 variants are still unknown. With differing terms and definitions, the number of long COVID phenotypes might grow exponentially, confusing stakeholders and preventing development of effective interventions.
Although long COVID can develop after acute illness of any severity and PICS is associated with recent critical illness, both are highly heterogeneous conditions. The term PICS, created by an international multidisciplinary group (including patient representatives) convened by the Society of Critical Care Medicine, was developed to increase awareness of long-term sequelae after critical illness among all relevant stakeholders. The patient-made origin of long COVID can also serve a similar role, being an overarching term covering broad sequelae and disease processes from acute infection. Other terms have much more rigid definitions, explicitly outlining symptom duration, and can be incorporated within the long COVID umbrella term.
With millions affected by COVID-19, the large number developing long COVID has major detrimental effects on people, society, and public health, including long-term follow-up, support, and lost productivity. There is an urgent need for unification of terminology for the sequelae of SARS-CoV-2 infection. Different terms may be used, but only if they are well defined and help ensure that research is directed towards and translated into interventional trials to improve the outcomes of people with long COVID. It is essential to bring together clinicians, researchers, patients, carers, funders, and policy makers to harmonise terminology. This is to help advance the field via improved harmonisation and comparability, while allowing for adjustment and flexibility in view of new discoveries.
DM reports grants from the British Embassy in Moscow, UKRI/NIHR, and the Russian Foundation for basic research funding projects related to COVID-19 and long COVID. DM is also a co-chair of the ISARIC Global Paediatric long COVID working group and member of the ISARIC working group on long-term follow-up in adults as well as co-lead of the PC-COS and PC-COS paediatric projects aiming to define the core outcome set for long COVID. DMN is a co-lead of the PC-COS project aiming to define the core outcome set for long COVID. EP reports being a Long Covid Kids Champion (an unpaid, volunteer role aimed at facilitating the recognition of long Covid in paediatric patients) for the charity Long Covid Kids. All other authors declare no competing interests.
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