Numbers of close contacts of individuals infected with SARS-CoV-2 and their association with government intervention strategies

Conor Teljeur,Francis Butler,Philip Nolan,Ciara Carroll,Martin J Green,Jennifer Martin,Eamonn Gormley,Patrick Wall,Sheila Doyle ,Bruce Smyth ,Cathal Walsh,Thomas Brendan Murphy ,Kieran Culhane,Jim Duggan,Luke O’Grady,Mary Codd,Conor G Mcaloon,Simon J More,Katie M O’brien ,Claire Buckley

doi:10.1186/s12889-021-12318-y

Abstract

BackgroundContact tracing is conducted with the primary purpose of interrupting transmission from individuals who are likely to be infectious to others. Secondary analyses of data on the numbers of close contacts of confirmed cases could also: provide an early signal of increases in contact patterns that might precede larger than expected case numbers; evaluate the impact of government interventions on the number of contacts of confirmed cases; or provide data information on contact rates between age cohorts for the purpose of epidemiological modelling. We analysed data from 140,204 close contacts of 39,861 cases in Ireland from 1st May to 1st December 2020.ResultsNegative binomial regression models highlighted greater numbers of contacts within specific population demographics, after correcting for temporal associations. Separate segmented regression models of the number of cases over time and the average number of contacts per case indicated that a breakpoint indicating a rapid decrease in the number of contacts per case in October 2020 preceded a breakpoint indicating a reduction in the number of cases by 11 days.ConclusionsWe found that the number of contacts per infected case was overdispersed, the mean varied considerable over time and was temporally associated with government interventions. Analysis of the reported number of contacts per individual in contact tracing data may be a useful early indicator of changes in behaviour in response to, or indeed despite, government restrictions. This study provides useful information for triangulating assumptions regarding the contact mixing rates between different age cohorts for epidemiological modelling.

Highlights

Contact tracing is conducted with the primary purpose of interrupting transmission from individuals who are likely to be infectious to others
During the contact tracing process, these data were entered into a Customer Relational Management (CRM) database called CovidCare Tracker, which was developed by the Health Service Executive (HSE) Office of the Chief Information Officer in collaboration with the HSE Contact Management Programme
After separating records according to the age cohort of the contact, Dataset 2 consisted of 251565 records

Summary

Introduction

Contact tracing is conducted with the primary purpose of interrupting transmission from individuals who are likely to be infectious to others. The effectiveness of the overall set of interventions might be determined by indicators of the rate of new infections in the population such as incidence rates (eg 14-day cumulative number of COVID-19 cases per 100,000 [6]) or time-varying reproduction numbers [7]. These indicators are by their nature somewhat retrospective and indirect. Given that the number of contacts is a key driver of onward transmission, changes in the numeric distribution of contacts per case may provide an early indication of changes in the trajectory of the number of cases over time

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Results

Discussion

Conclusion