Strategies to Increase the Impact of Contact Tracing and Review of Underlying Assumptions

Upon hearing of the contact tracing efforts in the Shire, the nearby Kingdom of Khazad-dûm has decided to implement a contact tracing program to reduce the spread of SARS-CoV-2. The Kingdom of Khazad-dûm Department of Health (KKDH) has collected the following data over the past four epidemiological weeks:

The Khazad-dûm population has an average household size of 1.5 (i.e., an average of 0.5 household contacts per case) and roughly 4 contacts outside of the household per person over the course of an infectious period. Due to the enclosed living conditions of their inhabitants, KKDH epidemiologists believe that R0 is 3 in their community, but that the natural history and other transmission assumptions should be like those found in previously studied locations. The two epidemiologists leading the KKDH contact tracing team have very different ideas on the best way to implement contact tracing. They have described their surveillance and isolation and contact tracing targets in the two proposals below.

Proposal A: Mildly expansive testing and case isolation with rapid and household-focused contact tracing

Surveillance detection targets:

• detect 30% of all infected people in the community with the surveillance program
• on average, isolate 600 newly detected cases each week
• on average, collect samples 2 days after symptom onset
• on average, isolate cases 4 days after symptom onset

Contact tracing targets:

• household contact tracing: 90% quarantined on the same day as case isolation, on average
• community contact tracing: 50% quarantined 2 days after case isolation, on average

Proposal B: Moderately expansive testing and case isolation with slower but complete contact tracing

Surveillance detection targets:

• detect 40% of infected people in the community with the surveillance program
• on average, isolate 1200 newly detected cases each week
• on average, collect samples 2 days after symptom onset
• on average, isolate cases 3 days after symptom onset

Contact tracing targets:

• household contact tracing: 90% quarantined 2 days after case isolation, on average
• Community contact tracing: 90% quarantined 4 days after case isolation, on average

Use the worksheet to prepare the ConTESSA inputs according to the two scenarios described above. Then, compare a Scenario A and Scenario B to answer the questions below (Hint: You will need to modify one of the Advanced Options).

Please select the correct statement after reviewing the results in the Dashboard.

Using the figure in the Surveillance tab of the Dashboard, what would be the estimated reproductive number under Proposal A if the percent of infections isolated who were not identified during contact tracing increased to ~55% (all else equal)?

Please enter a single numeric value rounded to two decimal places.

Using the figure in the Surveillance tab of the Dashboard, what would be the estimated reproductive number under Proposal B if the percent of infections isolated who were not identified during contact tracing increased to ~55% (all else equal)?

Please enter a single numeric value rounded to two decimal places.

After examining the figures in the Surveillance, Household, and Community tabs on the Dashboard, which performance metrics should be targeted for maximum impact on the reduction in R?

Please choose the response that would have maximum impact on both proposals.

You will not need to open the YAML input file that is saved to your computer; you will upload it to ConTESSA with the “Load Inputs” feature in Question 7 as is. If, however, you would like to open it, it can be viewed in any plain text editor (e.g., Notepad, TextEdit).

Have you selected “Save Inputs” and “Generate Report”?

Have you completed these steps?

For extra assistance in this question, return to the Advanced Options and change the slider for the relative transmissibility of an asymptomatic individual (person infected who never develops symptoms) vs symptomatic to 1 for both Proposals A and B. Then generate a report and compare the figures in the two reports that you have saved.