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).