Estimates of cases and hospitalizations averted by COVID-19 case investigation and contact tracing in 14 health jurisdictions in the United States

Jeon, S.; Rainisch, G.; Lash, R.; Moonan, P. K.; Oeltmann, J. E.; Greening, B.; Adhikari, B. B.; Meltzer, M. I.

Context: The implementation of case investigation and contact tracing (CICT) for controlling COVID-19 (caused by SARS-Cov-2 virus) has proven challenging due to varying levels of public acceptance and initially constrained resources, especially enough trained staff. Evaluating the impacts of CICT will aid efforts to improve such programs. Objectives: Estimate the number of COVID-19 cases and hospitalizations averted by CICT and identify CICT processes that could improve overall effectiveness. Design: We used data on proportion of cases interviewed, contacts notified or monitored, and days from testing to contact notification from 14 jurisdictions to model the impact of CICT on cumulative cases counts and hospitalizations over a 60-day period. Using the Centers for Disease Control and Prevention (CDC)'s COVIDTracer tool, we estimated a range of impacts by assuming either contacts would quarantine only if monitored or would do so upon notification of potential exposure. We also varied the observed program metrics to assess their relative influence. Results: Performance by jurisdictions varied widely. Jurisdictions isolated between 12 and 86% of cases (including contacts which became cases) within 6 to 10 days after exposure-and-infection. We estimated that CICT-related reductions in transmission ranged from 0.4% to 32%. For every 100 cases prevented by nonpharmaceutical interventions, CICT averted between 4 and 97 additional cases. Reducing time to case isolation by one day increased averted case estimates by up to 15 percentage points. Increasing the proportion of cases interviewed or contacts notified by 20 percentage points each resulted in at most 3 or 6 percentage point improvements in averted cases. Conclusions: We estimated that case investigation and contact tracing reduced the number of COVID-19 cases and hospitalizations among all jurisdictions studied. Reducing time to isolation produced the greatest improvements in impact of CICT.