Mapping Long COVID across the EU: definitions, guidelines, and surveillance systems in EU Member States: final report.

Background
A health crisis has arisen as an estimated 36 million people in the WHO European region suffer after a COVID-19 infection from persistent symptoms, termed "Long COVID" or "post-COVID conditions." Achieving a unified and effective response to Long COVID within the EU is challenging due to the diverse symptoms related to Long COVID and a lack of a generally accepted definition and diagnosis. The European Commission underscores the need for a harmonised approach, which has led to the establishment of the Network of Expertise on Long COVID (NELC) in 2023 to facilitate EU-wide collaboration. In order to support the work of the NELC, the EUHealthSupport Consortium was tasked to conduct a rapid mapping study. This mapping study aimes to provide insight into the current state of affairs regarding: 1) Long COVID definitions, 2) guidelines and intelligence on diagnosis and treatment, and 3) surveillance systems, as used/implemented EU Member States and beyond.

Methods
A search was conducted to map existing Long COVID and post-COVID definitions, guidelines, and intelligence on diagnosis, treatment, and surveillance systems in 34 selected countries. Documents were collected from EU Member States, Iceland, Norway, the United States, Canada, New Zealand, and Australia. The search encompassed online publications, reports, and guidelines from sources such as PubMed, national public health institutes, Long COVID primary care and medical specialist associations, patient associations, and global entities like WHO and OECD. Key search terms such as 'Long COVID,' 'Long COVID definition,' 'Long COVID treatment,' and others were employed, with translations into national languages.

Definitions of Long COVID
Long COVID definitions were identified in 33 out of 34 selected countries, with Lithuania being an exception. Commonly, these definitions align with WHO or National Institute for Health and Care Excellence (NICE) criteria, distinguishing between duration-based and non-duration-based definitions. Key elements include time criteria, persistent symptoms, ruling out alternative diagnoses, and including a broad range of symptoms. Variations exist in considering impact on daily life, organ system involvement, severity of the initial acute COVID-19 infection, and naming conventions. Insights from the ORCHESTRA study suggested to define several types of Long COVID, based on symptom combinations and their impact on physical and mental well-being.

Long COVID guidelines for diagnosis and treatment
The mapping study's second focus was on Long COVID guidelines for diagnosis and treatment. These were found across 21 out of 34 selected countries. Common elements include advocating a multidisciplinary approach, a central role for primary care, and the focus on rehabilitation. Some guidelines include recommendations for referral to specialised care and follow-up procedures. Guidelines differ in their target audience, addressing healthcare providers in general, secondary (specialised) care, decision makers, and interdisciplinary support involving municipalities. Guidelines also differ to some extent in addressing specific symptoms or organ systems that are affected by Long COVID. A quick literature search indicates that additional guidelines are still under development for various specific medical specialties and possible ways of treatment.

Long COVID surveillance
The third focus of the study was the mapping of Long COVID surveillance systems, initially using the search term 'surveillance system', with no result, and later 'registry.' Seven Long COVID registries were found in Australia, Germany, Spain, Sweden, the Netherlands, New Zealand, and the United States. In addition two additional registries, one from Germany and one from Czechia, were added after a review round among the NELC Members. Five of the mentioned Long COVID registries are based on self-registration. The Spanish registry involves primary care professionals in recruitment and the Swedish registry is based on registration data. The Australian registry uniquely allows carers to register as well. Data linkage to other sources is specified only in the New Zealand registry. Notably, except for the Swedish and one of the German registries, none of the registry websites provide insights gained or expected timelines for results. As limited information is available for most registries, a detailed understanding of their structures and goals in comparison to others is hindered.
Some countries, including Bulgaria, Italy, Germany, and Ireland, have implemented clinical centers for Long COVID patients from which data can be collected that may serve as an alternative source of information on the Long COVID population. Similarly, several countries have implemented or are implementing cohort studies for Long COVID patients.

Reflections and conclusion
This rapid mapping study underlines the interconnectedness of Long COVID definitions, the development of guidelines, and surveillance systems. A clear definition is crucial for developing effective guidelines and surveillance, but defining Long COVID is still challenging due to the broad range of symptoms involved. The ORCHESTRA project's multi-type definition may enhance refined guidelines and surveillance. It can be concluded that in most EU Member States guidelines for the diagnosis and treatment of Long COVID need to be developed or need to be made publicly available. Member States in which guidelines are available could serve as an example.

Given the variability in definitions and the voluntary entry of patients into the existing registries, there are no good estimates yet of the total numbers of patients and the severity of their disease in EU Member States. Linking information from cohort studies and clinical trials may be necessary to provide the full picture of the burden of disease of Long COVID.