Chasing the ghost of infection past: identifying thresholds of change during the COVID-19 infection in Spain

Luis Santamaria; Joaquin Hortal

Several factors make Spanish data one of the most fair accounts of the effects of the pandemic at the country and regional levels, together with Italy and, specially, South Korea. Although the lack of enough tests that has been pervasive for most countries (except South Korea), Spain has achieved one of the highest infection test ratios per capita (Clark et al. 2020) , thanks to the early mobilisation of most PCR machines available in universities and research centres for either COVID-19 testing or COVID-19 research. Importantly, only cases testing positive in the PCR make it to the official statistics -and (similar to Italy but different to other European countries) all deaths testing positive are registered as caused by COVID-19 infection, including those associated with previous pathologies or happening outside hospitals (e.g. in private homes and nursing homes). These data provide an underestimation of the total population infected and the number of fatalities-due to the limited number of tests; although for the number of deaths this is partly compensated by the lethality associated to other pathologies that is attributed to COVID-19 when PCRs render positive tests. However, the relatively homogeneous intensity of testing and the stability of criteria for disease attribution throughout the time period of this analysis probably result in unbiased estimators for the spread of the pandemic. It is therefore safe to assume that the number of reported cases of infection and the number of deaths are reasonably good proxies for the advance of the pandemic.