Discontinuous epidemic transition due to limited testing

TL;DR

This paper demonstrates that limited testing capacities can cause a sudden, discontinuous shift in epidemic dynamics, leading to super-exponential growth and increased uncertainty in containment outcomes.

Contribution

It reveals how testing limitations induce a discontinuous epidemic transition, fundamentally altering the effectiveness of containment measures.

Findings

Limited testing causes super-exponential outbreak growth.

Containment success is highly sensitive to testing capacity.

Epidemic transition becomes discontinuous under testing constraints.

Abstract

High impact epidemics constitute one of the largest threats humanity is facing in the 21st century. Testing, contact tracing and quarantining are critical in slowing down epidemic dynamics, but may prove insufficient for highly contagious diseases. In the absence of pharmaceutical interventions, physical distancing measures remain as the last resort to avoid a widespread outbreak. Here we show that such combined countermeasures drastically change the rules of the epidemic transition if testing capacities are limited: Instead of continuous the response to countermeasures becomes discontinuous and rather than following the conventional exponential growth, the outbreak accelerates and scales super-exponentially during an intermediate period. As a consequence, containment measures either suffice to stop the outbreak at low total case numbers or fail catastrophically if marginally too weak, thus implying large uncertainties in reliably estimating overall epidemic dynamics, both during initial phases and during second wave scenarios.