Importance of untested infectious individuals for the suppression of COVID-19 epidemics

Francisco Perez-Reche; Norval Strachan

The obtained values for the testing rate reveal that during the early stage of outbreaks, Germany scored the highest in terms of testing for infection (median 53%). Hubei follows Germany in terms of testing, followed by Spain, Italy and the UK. Our prediction for Hubei is not far from the 65% reporting rate estimated by Li et al. 11 for China in the period considered here. The high testing rate predicted for Germany agrees with the known high testing capacity in this country 27 . Taking the confidence intervals into account, we estimate that for each infected individual tested in the UK, there could have been between 2 and 10 untested infected individuals. At the other end of the testing spectrum, we estimate that for each infected individual tested in Germany, between 0.2 and 2 individuals might have not been tested at the beginning of the epidemic. A higher testing rate for Germany is in qualitative agreement with estimates given elsewhere 22, 26 . Our estimates for the reporting rate, however, tend to be higher than those obtained by Jagodnik et al. 26 and the differences we found between countries are not as extreme as those given by Chicci et al. 22 Assuming that the testing rate remains constant during the course of epidemics and no control interventions are implemented, our model predicts that the number of tested and untested infected individuals would evolve in parallel in all the studied outbreaks which would last for around 12 weeks in all cases (see Figure 3 ). We see, however, that the epidemic in Germany would belong to a different class in the sense that the number of untested infected individuals remains smaller than the number of tested individuals during the whole epidemic. Italy, Spain and UK exhibit the opposite behaviour with more untested than tested individuals. For Hubei, we predict similar levels of untested and tested rates. Obviously, these predictions will not be fulfilled since control interventions are imposed in all these countries and testing strategies might change during the pandemic.