  Infectious diseases that spread silently through asymptomatic or
pre-symptomatic infections represent a challenge for policy makers. A
traditional way of achieving isolation of silent infectors from the community
is through forward contact tracing, aiming at identifying individuals that
might have been infected by a known infected person. In this work we
investigate how efficient this measure is in preventing a disease from becoming
endemic. We introduce an SIS-based compartmental model where symptomatic
individuals may self-isolate and trigger a contact tracing process aimed at
quarantining asymptomatic infected individuals. Imperfect adherence and delays
affect both measures. We derive the epidemic threshold analytically and find
that contact tracing alone can only lead to a very limited increase of the
threshold. We quantify the effect of imperfect adherence and the impact of
incentivizing asymptomatic and symptomatic populations to adhere to isolation.
Our analytical results are confirmed by simulations on complex networks and by
the numerical analysis of a much more complex model incorporating more
realistic in-host disease progression.
