Several tracing studies have been published, some focussing on specific infections [10, 11] and some with the objective to obtain more general insight, e.g. in a general Markov-type SIR model [7] , in a model incorporating symptom development [4] , or in simulation models with specific network contact structures [8, 9] . Different assumptions were made with regard to the possibility of only tracing contacts of symptomatic infecteds (single-step tracing [4, 10, 11] ), or of iteratively tracing the contacts of traced infecteds (iterative tracing [6] [7] [8] [9] ). However, no general insight has yet been obtained in reducing R pre in relation to time-related characteristics of the infection and the tracing process, such as the latent and infectious periods, the time of symptom-based detection, and delays in the tracing process.