The goal of this observational study is to deepen our understanding of long COVID by determining the prevalence of the main complications and medium- to long-term sequelae of COVID-19 in Navarre.

Sociodemographic variables such as age, sex, ethnicity, smoking history, and comorbidities will be collected, as well as clinical and disease management variables such as persistent COVID-19 symptoms at 3 months, all with the aim of characterizing patients with long COVID.

All patient data will be collected in a single visit.

COVID-19 is the largest pandemic faced by the public health system in the last hundred years. The medium- and long-term consequences of SARS-COV-2 infection are currently unknown. Studies on coronavirus-induced lung damage in previous epidemics such as SARS-CoV and MERS-CoV have shown an increase in morbidity and mortality due to pulmonary fibrosis as a consequence of adult respiratory distress syndrome (ARDS) caused by these viruses. COVID-19 has also been shown to be a multisystemic disease with the potential to affect multiple organs or systems, damaged directly by the virus and/or indirectly by a dysfunctional immune response and/or by the supportive therapies used.

The healthcare system is currently focusing on the acute care of this disease, but continuous monitoring of these patients is necessary since many of them continue to have symptoms after the acute phase of the disease, known as persistent COVID-19 or long COVID. Long COVID or persistent COVID is the term used to describe the disease in people who have recovered from the disease but still report lasting effects from the infection or who have symptoms for longer than would be expected².

The study published by Carfi et al, conducted in a hospital in Rome, has shown that 9 out of 10 patients (87%) who had been discharged from hospital with COVID-19 60 days after discharge still reported at least one symptom of COVID-19³.

The investigators believe that once this peak phase of the epidemic has passed, it is very important to monitor the progress of patients who have suffered a moderate or severe infection in order to assess the presence of complications in the medium and short term. For this reason, it is necessary to implement a coordinated care protocol for patients diagnosed with persistent COVID-19 or with sequelae, involving both primary and hospital care, with a specific monographic consultation, as has been done in other centres⁴ and as agreed between the Spanish Society of Internal Medicine (SEMI) and the Spanish Society of Primary Care Physicians (SEMERGEN)⁵.

The establishment of a specific care pathway for persistent COVID patients, together with the creation of a registry of these patients that collects information on their demographic and clinical characteristics, will make it possible to determine the prevalence of complications in this population and will provide the infrastructure and basis necessary for carrying out future short- to medium-term clinical projects aimed at the prevention and treatment of persistent COVID disease in Navarra.

The overall objective of this project is to deepen our understanding of persistent COVID disease in our environment. This overall objective will be carried out in accordance with the following specific objectives:

1. Establish an effective and coordinated care pathway between primary care and hospital care specifically for persistent COVID patients, facilitating comprehensive care and follow-up while avoiding duplication and overlap of consultations.
2. Generate a registry of patients with persistent COVID-19 in Navarre (PersiCOV-19) through the prospective collection of sociodemographic, clinical, and analytical information on these patients.
3. Describe the demographic, clinical, and analytical characteristics of patients with persistent COVID in our setting.
4. Establish the prevalence of different symptoms, complications and/or medium- to long-term sequelae of COVID-19 in Navarre.
5. Record the use of the different therapeutic options used to prevent and/or treat potential complications.
6. Analyse the possible factors that condition the presence of certain complications.

The work plan is as follows:

Register patients seen in outpatient consultations at the Internal Medicine Department of the Navarra Hospital Complex who have been referred from Primary Care, from the Internal Medicine Department of the Navarra Hospital Complex itself, or from other departments.

Patient registration will begin in January 2021 and end in December 2026. Patients assessed by Primary Care Teams (Primary Care Physician or Case Management Nurse) who present symptoms compatible with persistent Covid will be referred to the Internal Medicine clinic.

Patients who have been assessed in outpatient clinics by professionals from other specialities and who present symptoms compatible with persistent Covid will be referred to the Internal Medicine clinic.

It is recommended that patients undergo the following procedures before referral:

• a clinical assessment questionnaire (Annex 1), which may be conducted by telephone and/or in person
• a blood test including a complete blood count, coagulation, CRP, ferritin, LDH, liver and kidney profile
• a chest X-ray.

If they do not have these, they will be carried out at the Internal Medicine clinic.

If the symptoms are debilitating and prevent the patient from carrying out an active working and daily life, they may be referred to the Internal Medicine clinic on a priority basis within 3 months.

This study is an observational, descriptive, cross-sectional, prospective cohort study that will include patients seen in the outpatient clinic of the Internal Medicine department who have been referred from primary care teams or other departments.

The sociodemographic and clinical characteristics of the study population and the treatments received will be described using descriptive statistics such as mean and standard deviation or median and interquartile range for continuous variables, depending on their nature, and frequencies and percentages for categorical variables. The prevalence of certain complications and sequelae in this population will be estimated using frequencies and their 95% CI. If any comparisons are made between patients with certain complications, these will be performed using parametric techniques such as Student's t-test or non-parametric techniques such as Mann-Whitney's U test for quantitative variables and the Chi-square test or Fisher's test for qualitative variables. Data analysis will be performed using statistical programmes such as the free software R 4.0.2 or IBM SPSS Statistics 21.

The fact that the registry is an observational study of a single cohort of patients with persistent COVID (without a comparison group) will have limitations in that it will not be possible to establish risk factors or possible causes related to the development of persistent COVID, and the investigators may encounter biases such as sample selection and recall bias.

Inclusion Criteria:

• History of confirmed SARS-CoV-2 infection
• Presentation of symptoms that have persisted for more than 3 months after SARS-CoV-2 infection
• The patient reports any of the symptoms listed in the clinical assessment questionnaire or checklist.

Exclusion Criteria:

• The symptom(s) referred to already existed prior to acute SARS-CoV-2 infection.

Patients seen in the Internal Medicine outpatient clinic who have been referred by primary care teams or other medical services.