Cite as:

Chen Shen, Ron Mark, Nolan J. Kagetsu, Anton S. Becker, and Yaneer Bar-Yam, Combining PCR and CT testing for COVID, medRxiv (May 29, 2020).

Abstract

We analyze the effect of using a screening CT-scan for evaluation of potential COVID-19 infections in order to isolate and perform contact tracing based upon a viral pneumonia diagnosis. RT-PCR is then used for continued isolation based upon a COVID diagnosis. Both the low false negative rates and rapid results of CT-scans lead to dramatically reduced transmission. The reduction in cases after 60 days with widespread use of CT-scan screening compared to PCR by itself is as high as 50x, and the reduction of effective reproduction rate R(t) is 0:20. Our results imply that much more rapid extinction of COVID is possible by combining social distancing with CT-scans and contact tracing.

Fig. 2. As in Fig.1 but with a stronger social interventions so that R*=1:06. We choose the R* so that in test strategy 1, infection rates are nearly constant. The first few days have sharp drop due to the change in testing and isolation strategy (see methods).

Fig. 3. Illustration of a simulation similar to Fig. 2, orange curve (widespread PCR tests, no CT use). Simulation starts at day 0 (horizontal axis) with 10 individuals and runs for 60 days with R*=1.06. Vertical axis indicates each infected individual. Horizontal bars represent individual history from infection to symptoms, testing and isolation. Transmission shown by thin red line. Colors represent: pink → presymptomatic, orange → mild, red → severe, yellow → asymptomatic, green → isolated, and black box → PCR test. Inset shows histogram of total number of infected individuals in the simulation (vertical axis is frequency), with the main panel showing an example with close to the median number of infections, 86.

Fig. 4. Illustration of a simulation similar to Fig. 2, blue curve (widespread CT-scan and PCR tests). Other parameters are the same as in Fig. 3. Dashed blue box → CT-scan, PCR for COVID diagnosis not shown. Fewer infected individuals (median 38) reflects the effectiveness of CT-scans and isolation in preventing transmission. Note that the last infection is on day 21, while with RT-PCR in Fig. 3 the outbreak doesn’t stop in 60 days.

Fig. 1. Daily new infections with three testing strategies and without and with contact tracing, average of 60 simulation runs (see text). For dotted lines 50% of close contacts are quarantined. Reference reproduction rate due to moderate social interventions is R*=1:25 (see methods).

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