Coronavirus (COVID-19) Collection
- Madrid has been the epicenter of COVID-19 in Spain, primarily due to its high population density and mobility. The city has 3.3 million people, with 6.8 million across the metropolitan area. Up to March 15 2021, roughly 605 000 persons had been diagnosed with SARS-CoV-2 infection and 14 000 had died in the Madrid region (Ministerio de Sanidad, 2021; Instituto Nacional de Estadística, 2021). These figures refer to laboratory-confirmed cases, which underestimate the true number as testing access was limited during the earlier stages of the pandemic (Soriano and Barreiro, 2020).
- The emergence and rapid global spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), from Wuhan, China at the end of 2019 represented an unprecedented phenomenon in medicine. COVID-19 continues to challenge health services and disrupt social and economic activities globally. In Spain, the first wave commenced in mid-March 2020 and lasted for 3 months. It finally abated due to strict lockdown and home confinement. Following relaxation of measures during the summer, a second wave commenced in mid-September 2020 and extended until Christmas 2020.
- A relationship between the infecting dose and the risk of disease severity has been demonstrated for several viral infections, including influenza and SARS (Hijano et al., 2019; Chu et al., 2004). For COVID-19, high viral loads either in saliva, respiratory secretions, or blood have been associated with more severe illness (Xu et al., 2020; To et al., 2020). However, it remains unclear whether exposure to a greater viral inoculum could determine a higher risk for developing severe COVID-19. Although intuitive, it has been challenging to obtain such dose-response data.