[Paper Review] Contact Tracing & Super-Spreaders in the Branching-Process Model

Johannes Müller, Hösel|arXiv (Cornell University)|Apr 10, 2021

COVID-19 epidemiological studies38 references4 citations

TL;DR

This paper proposes a branching-process model to study contact tracing in the context of super-spreader events, where infections occur synchronously due to random contact rates rather than heterogeneous networks. It finds that contact tracing remains effective under SARS-CoV-2 parameters, especially when symptomatic cases are rare, tracing is efficient, or latency exceeds incubation periods, though super-spreaders can reduce tracing efficacy in other scenarios.

ABSTRACT

In recent years, it became clear that super-spreader events play an important role, particularly in the spread of airborne infections. We investigate a novel model for super-spreader events, not based on a heterogeneous contact graph but on a random contact rate: Many individuals become infected synchronously in single contact events. We use the branching-process approach for contact tracing to analyze the impact of super-spreader events on the effect of contact tracing. Here we neglect a tracing delay. Roughly speaking, we find that contact tracing is more efficient in the presence of super-spreaders if the fraction of symptomatics is small, the tracing probability is high, or the latency period is distinctively larger than the incubation period. In other cases, the effect of contact tracing can be decreased by super-spreaders. Numerical analysis with parameters suited for SARS-CoV-2 indicates that super-spreaders do not decrease the effect of contact tracing crucially in case of that infection.

Motivation & Objective

• To understand how super-spreader events affect the efficiency of contact tracing in infectious disease spread.
• To model super-spreading not through heterogeneous contact networks but via random, high-contact-rate events.
• To evaluate the impact of key epidemiological parameters—such as symptom fraction, tracing probability, and latency vs. incubation periods—on contact tracing outcomes.
• To assess whether super-spreaders diminish the effectiveness of contact tracing, particularly in the context of SARS-CoV-2.

Proposed method

• Uses a branching-process framework to model disease spread with super-spreader events as synchronized infection events.
• Models contact tracing as a stochastic process without tracing delay, assuming immediate identification of contacts.
• Introduces a random contact rate mechanism to generate clusters of simultaneous infections, representing super-spreader events.
• Analyzes the basic reproduction number and final outbreak size under varying transmission and tracing parameters.
• Compares outcomes under different combinations of symptom fraction, tracing probability, and relative durations of latency and incubation periods.
• Performs numerical simulations using parameters relevant to SARS-CoV-2 to assess real-world applicability.

Experimental results

Research questions

• RQ1 How does the presence of super-spreader events affect the efficiency of contact tracing in a branching-process model?
• RQ2 Under what conditions does contact tracing remain effective despite super-spreading?
• RQ3 How do the relative durations of the latency and incubation periods influence contact tracing outcomes?
• RQ4 What role does the fraction of symptomatic individuals play in determining the effectiveness of contact tracing in super-spreading scenarios?
• RQ5 To what extent do super-spreaders diminish the impact of contact tracing under SARS-CoV-2-relevant parameters?

Key findings

• Contact tracing remains effective in the presence of super-spreaders when the fraction of symptomatic individuals is low.
• High tracing probability enhances the effectiveness of contact tracing, even in super-spreading scenarios.
• When the latency period is significantly longer than the incubation period, contact tracing is more effective despite super-spreading.
• Super-spreaders can reduce the effectiveness of contact tracing when the above conditions are not met.
• Numerical analysis with SARS-CoV-2 parameters shows that super-spreaders do not critically diminish the impact of contact tracing.