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

Luis Santamaria; Joaquin Hortal

(1) A first phase, in the early moments of the epidemic, characterized by sudden (apparent) jumps in the number of infections, particularly conspicuous in Madrid, which were not accompanied by increases in the infection rate. This phase coincided with the detection of the first cases, imported from abroad; and the two jumps in the number of infections were synchronous with specific events of group infections (at sport events and nursing homes, respectively; red points 4 and 7 in Figure 5 ). Owing to the lag times mentioned above, the effects of this phase become perceivable between March 1 and March 8. During this phase, however, breaking points signaling one (Madrid) and two (Spain) consecutive decreases in the growth rates of the number of deaths were identified (37-40% and 56% decreases in Spain and Madrid, respectively). These breaking points could not be linked to any specific event or policy measure, and were probably related to the improvement of clinical procedures (detection and hospital treatment) following the detection, hospitalization -and, in some cases, death of the first cases.