Cohort profile: a multicenter European study of acute respiratory infections: the MERMAIDS-ARI 2.0 cohort study

Purpose: Multi-centre EuRopean study of MAjor Infectious Disease Syndromes Acute Respiratory Infections (MERMAIDS-ARI) cohort study is a European prospective cohort study. It was originally launched in 2016 as MERMAIDS-ARI to study acute respiratory infections. When the COVID-19 pandemic hit, the study re-started inclusion under an amended protocol as MERMAIDS-ARI 2.0 focusing on SARS-CoV-2. The objectives of this study were to describe the disease spectrum, clinical features, and outcomes of SARS-CoV-2 infections in hospital care, to determine relevant risk factors and the assess prevalence and within hospital spread compared to other respiratory infections. An important second objective was to establish an extensive biobank supplemented with detailed clinical data to be able to address future virological, immunological, and clinical research questions. Methods: Patients with either 1) ARI presenting to hospital care during the SARS-CoV-2 epidemic (including both COVID-19 and non-COVID-19 patients) or 2) confirmed COVID-19 infection, but with atypical presentation (non-ARI) or with nosocomial acquisition were included. Clinical data and biological samples were collected on enrolment day and repeatedly thereafter until discharge. A subset of COVID-19 patients was also followed up to 12 months post-discharge to study clinical recovery and long-term sequelae. Findings to date: In total 297 patients from 8 countries and 11 sites were recruited between June 2020 and September 2021. We reached high sample completeness for most sample types (>97% for single samples and >86% for serial samples). 294 (99.0%) patients were admitted to hospital with SARS-CoV-2. The population primarily consists of patients (median age 61 years) of Caucasian ethnicity, with the majority being male (62.0%) and having ≥1 comorbidities (67.3%). The median hospital stay was 10 days, and most patients (87.5%) received treatment with systemic corticosteroids and respiratory support (81.4%). A total of 64 (21.7%) patients were admitted to the Intensive Care Unit (ICU), and 6.5% died during hospitalization. Long-term follow-up of 94 patients revealed that most individuals resumed their regular activities and work within three months, with improvements observed in mobility and personal care over time. Instances of severe and extreme pain and anxiety were rarely reported (≤1.1%). Conclusion: This pan-European study offers a valuable resource for conducting in-depth virological, immunological, and pathophysiological investigations pertaining to SARS-CoV-2. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work is supported by RECOVER (Rapid European COVID-19 Emergency research Response), which has received funding from the EU Horizon 2020 Research and Innovation program [grant agreement number 101003589]. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Regulatory approvals were sought in each country. The following Ethics Boards were consulted: Medical Ethics Committee of the: University Medical Centre Utrecht-the Netherlands, Clinical Center of Serbia-Serbia, Clinical Centre of Kragujevac-Serbia, Tartu University Clinic-Estonia, Attikon University General Hospital-Greece, Brescia Hospital-Italy, Clinic Center of Podgorcia-Montenegro, National Institute for Infectious Diseases Prof. Dr. Matei Bals-Romania, University Hospital Brothers Trias I Pujol-Spain, HU Virgen Macarena-Spain and the Regional Hospital de M Laga-Spain. Dates of approval letters and/or numbers available on request. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors