Fig. 7: Symptom-driven testing and contact tracing need to be combined to control the disease.
From: The challenges of containing SARS-CoV-2 via test-trace-and-isolate

Stability diagrams showing the boundaries (continuous curves) between the stable (controlled) and uncontrolled regimes for different testing strategies combining random testing (rate λr), symptom-driven testing (rate λs), and tracing (efficiency η). Gray lines in plots with λr-axes indicate capacity limits (for our example Germany) on random testing (\({\lambda }_{r,\max }\)) and when using pooling of ten samples, i.e., \(10{\lambda }_{r,\max }\). Colored lines depict the transitions between the stable and the unstable regime for a given reproduction number \({R}_{t}^{H}\) (color-coded). The transition from ‘stable" to ‘unstable" case numbers is explicitly annotated for \({R}_{t}^{H}=1.5\) in panel a. a Combining tracing and random testing without symptom-driven testing is in all cases not sufficient to control outbreaks, as the necessary random tests exceed even the pooled testing capacity (\(10{\lambda }_{r,\max }\)). b Combining random and symptom-driven testing strategies without any contract tracing requires unrealistically high levels of random testing to control outbreaks with large reproduction numbers in the hidden pool (\({R}_{t}^{H}> 2.0\)). The required random tests to significantly change the stability boundaries exceed the available capacity in Germany \({\lambda }_{r,\max }\). Even considering the possibility of pooling tests (\(10{\lambda }_{r,\max }\)) often does not suffice to control outbreaks. c Combining symptom-driven testing and tracing suffices to control outbreaks with realistic testing rates λs and tracing efficiencies η for moderate values of reproduction numbers in the hidden pool, \({R}_{t}^{H}\), but fails to control the outbreak for large \({R}_{t}^{H}\). The curves showing the critical reproduction number are obtained from the linear stability analysis (Supplementary Eq. (1)).