METHODS
This is a retrospective study of a cohort of patients diagnosed with COVID-19 in the Basque Country based on data from the electronic database and health records of the Basque health service, Osakidetza.
All patients included in this study were residents in the Basque Country who had a SARS-CoV-2 infection, laboratory-confirmed by a positive result on the reverse transcriptase-polymerase chain reaction assay for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or a positive antigen test between March 1, 2020 and January 9, 2022. From March 1, 2020 to July 31, 2020, positive IgM or IgG antibody tests performed due to patients having symptoms suggestive of the disease or having had contact with a positive case were also included in the sample. The first positive from each patient was collected. Only patients aged over 18 years were included. The study protocol was approved by the Ethics Committee of the Basque Country (reference PI2020123). All patient data was kept confidential.
All data on patients under the care of Osakidetza are held in a unified electronic database. Analysts retrieved data from all positive cases detected during the study period, including sociodemographic data; baseline comorbidities (all those included in Charlson’s Comorbidity Index2 plus angina, arrhythmia, arterial hypertension, dyslipidemia, asthma, bronchiectasis, cystic fibrosis, interstitial lung disease, lymphoma, leukemia, coagulopathy, inflammatory bowel disease and gastrointestinal bleeding); baseline treatments (based on the Anatomical, Therapeutic, Chemical [ATC] classification system); other background data related to care provided in hospital or primary care settings, including dates of hospital admission and discharge and whether patients were admitted to an intensive care unit (ICU); and vital status. Comorbidities were identified based on the International Statistical Classification of Diseases and Related Health Problems (ICD) ICD-9 or 10 codes in the patients’ records at baseline.
Comorbidities were grouped as follows: cardiovascular diseases (including myocardial infarction, angina, arrhythmia, congestive heart failure, and peripheral vascular disease); cerebrovascular disease, hemiplegia and/or paraplegia; arterial hypertension; dyslipidemia; dementia; interstitial pulmonary disease, cystic fibrosis, respiratory disease (chronic obstructive pulmonary disease [COPD], bronchiectasis, chronic bronchial infection); asthma; liver disease (mild, moderate or severe); diabetes (with/without organ damage); kidney disease; cancer (malignant tumor, metastatic solid tumor, lymphoma); rheumatic disease; peptic ulcer; inflammatory bowel disease; and coagulopathies.
For baseline medication, we selected drugs based on ATC codes. Baseline treatment was defined as any drugs prescribed before diagnosis with SARS-CoV-2 infection and had no end date. Data identifying residents of nursing homes were obtained from the Basque Health Department.
The outcomes used in the study were as follows: 1.- Hospital admission due to COVID-19, defined if admission occurred within 15 days of the patient’s testing positive, when the positive test preceded hospitalization, and up to 21 days after admission when the patient tested positive during hospitalization; 2.-Death during the three months following diagnosis or during a hospital admission as defined previously; 3.- Adverse evolution, including death or ICU admission during a hospital admission related to a SARS-CoV-2 infection diagnosis as defined above. All patients were monitored to April 9, 2022. The period from March 1st, 2020 to December 13, 2021 was considered as a sample for model development (hereinafter referred to as the Derivation Data Set), while the period from December 14 to January 9, 2022, corresponding to the Omicron variant wave was used to validate the consistency of the results obtained (hereinafter referred to as the Omicron - Validation Data Set).