In this paper, we present a comprehensive, yet simple, extension to the existing systems used for Digital Contact Tracing in Covid-19 pandemic. The ex-tension, called BubbleAntiCovid19 (BAC19), enables those systems, regardless of their underlying protocol, to enhance their sets of traced contacts and to improve the global fight against pandemic during the phase of opening borders and enabling more traveling. BAC19 is a Structured Overlay Network. Its protocol is inspired by the Chord and Synapse Structured Overlay Networks. We design the architecture of the Overlay Network Federation. We show that the federation can be used as a formal model of Forward Contact Tracing. BAC19 provides a fully exhaustive retrieving procedure thanks to avoiding search during peer churn. Furthermore, we give simulation results for the BAC19 system, the simulator written in Python.