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Chronic Obstructive Pulmonary Disease (COPD) does not appear to be a predisposing factor for SARS-CoV-2 infection. However, once infection occurs and the disease develops, there is an increased risk of hospital admission, admission to intensive care unit (ICU) and death. Furthermore, the respiratory symptoms of COVID-19 may sometimes be confused with COPD exacerbations, which may delay diagnosis and affect the clinical course. The underlying pathophysiological mechanism would be an increased expression of ACE2 receptors (to which the virus binds to penetrate the cell) in the bronchial epithelium, amongst others.

'''HYPERTENSION'''

Hypertension is an important risk factor that has been discovered in 19% of patients with COVID-19 in Spain. The biological concept is based on its effect on the renin-angiotensin-aldosterone system and on angiotensin-converting enzyme 2 (ACE-2) overexpression.

'''OBESITY'''

Obesity is considered the epidemic of the 21st century, as its numbers are increasing in the adult population and, what is more worrying, in children. Being overweight/obese has been identified in numerous studies as a predictor of hospital admission and admission to the ICU, especially in patients under 65 years of age. The SEMI-COVID-19 registry shows its presence in 21% of patients.

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This risk factor has been identified in 17% of the cases reported (8.9% of hospital admissions in Spain). It is clearly a higher risk factor for hospital admission, admission to the ICU and death. The biological mechanism on which this risk factor is based is that described for hypertension.

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Heart failure has been described, either under this term or as a cardiovascular disease, as the most prevalent risk factor in the population diagnosed with COVID-19 (up to 30%) and is present in more than 50% of COVID-19 patients admitted to the ICU in Spain, according to several studies. Its mechanism of action is the same as for diabetes and hypertension.

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Chronic Kidney Disease (CKD) is included in the range of comorbidities that are associated with worse COVID-19 outcomes. Kidneys have ACE-2 receptors and are primarily involved in the renin-angiotensin-aldosterone system that regulates blood pressure. These are usually patients with added comorbidities, such as diabetes and hypertension, who have a weakened immune system.

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HIV infection and AIDS diagnosis is not usually listed as a risk factor in most studies as such; immunodeficiency is. However, this term is very broad and difficult to define. So a pathology like VIH-AIDS, with a well-established information system and a clear impact on the immune system, especially cell-mediated immunity, was opted for in this study.