Single-step contact tracing of infectious nodes I/R. Diagnostic tests are often necessary to determine the status of traced nodes (individuals); these may be imprecise or slow and the isolation and observation of traced individuals may not be a viable option. In such cases, multiple-step contact tracing is less likely. In an alternative single-step contact-tracing model, the infectious neighbours of triggering nodes are traced at rate 4 per contact. These are then directly removed and do not initiate further tracing. Control is always modelled through either multi-step or single-step tracing.