Effectiveness of Contact Tracing on Viral Disease Mitigation and Suppression: An Evidence-Based Review (Preprint)

BACKGROUND Contact tracing in association with quarantine and isolation is an important public health tool to control outbreaks of infectious diseases. This strategy has been widely implemented in the current coronavirus disease 2019 (COVID-19) pandemic. The effectiveness of this non-pharmaceutical intervention (NPI) is largely dependent on social interactions within the population and its combination with other interventions. Given the high transmissibility of SARS-CoV-2, small serial intervals, and asymptomatic transmission patterns, the effectiveness of contact tracing for this novel agent is largely unknown. OBJECTIVE To identify and synthesize evidence regarding the effectiveness of contact tracing on infectious viral disease outcomes based on prior scientific literature. METHODS An evidence-based review was conducted to identify studies from MEDLINE (including pre-print medRxiv server content) related to the effectiveness of contact tracing in viral outbreaks. The search dates were from database inception to July 24, 2020. Outcomes of interest were measures of incidence, transmission, hospitalization, and mortality. RESULTS Out of 159 unique records retrieved, 45 records were reviewed at the full-text level, with 24 meeting all inclusion criteria. Included studies utilized mathematical modeling (n=14), observational (n=8), and systematic review (n=2) approaches. Only two studies considered digital contact tracing. Contact tracing was mostly evaluated in combination with other NPIs and/or pharmaceutical interventions (PIs). While some degree of effectiveness in decreasing viral disease incidence, transmission, and resulting hospitalizations and mortality was observed, these results were highly dependent on epidemic severity (R0 value), number of contacts traced (including pre-symptomatic and asymptomatic cases), timeliness, duration, and compliance with combination interventions such as isolation, quarantine, and treatment. Contact tracing effectiveness was particularly limited by logistical challenges associated with increased outbreak size and speed of spread. CONCLUSIONS Timely deployment of contact tracing strategically layered with other NPIs could be an effective public health tool for mitigating and suppressing infectious outbreaks by decreasing viral disease incidence, transmission, and resulting hospitalizations and mortality.