In the event of an epidemic, testing plays a crucial role not only in surfacing the underlying disease dynamics but also in mitigating its spread through (at least) two mechanisms: after a positive test, (1) individuals can be removed from the pool of infections via test-trace-and-isolate, which reduces the overall force of infection in the population. (2) Individuals may adapt their behavior to protect themselves and others.

In this talk, Sebastian Contreras will discuss recent findings regarding the feasibility of controlling epidemics through testing and its interaction with behavioral interventions, focusing on two types of infections: respiratory pathogens and sexually transmitted infections (STIs). First, they will examine how complex dynamics can emerge around the endemic equilibrium of respiratory diseases subject to delayed mitigation and seasonal changes in contact patterns. This indicates the existence of an implicit social trade-off, where the dynamics stabilize around a chaotic attractor that features lower average infections rather than following a predictable limit cycle.

Next, using STIs as a case study, we will see that increased testing may generate paradoxes where observed trends seem to increase while the true STI prevalence decreases, and use a model to reconcile conflicting observational evidence. Characterizing the parameter space where such a paradox emerges is critical for correctly assessing the effectiveness of public health interventions, such as the HIV pre-exposure prophylaxis (PrEP).