Routine testing of close contacts of confirmed COVID-19 cases – National COVID-19 Contact Management Programme, Ireland, May to August 2020

Highlights

• More asymptomatic close contacts were identified than symptomatic close contacts.

• Application of symptom-based criteria for testing in this high-incidence population is of limited utility.

• The secondary attack rate in close contacts who were tested was 7% (95% CI: 6.3–7.8%).

• The number of close contacts needed to test at ‘day 0’ to identify one case was 15, and 63 at ‘day 7’.

Abstract

Objectives

The objective of this study was to inform public health practitioners who are designing, adapting and implementing testing and tracing strategies for Coronavirus disease (COVID-19) control.

Study design

The study design is monitoring and evaluation of a national public health protection programme.

Methods

All close contacts of laboratory-confirmed cases of COVID-19 identified between the 19th May and 2nd August were included; secondary attack rates and numbers needed to test were estimated.

Results

Four thousand five hundred eighty six of 7272 (63%) close contacts of cases were tested with at least one test. The secondary attack rate in close contacts who were tested was 7% (95% Confidence Interval [CI]: 6.3 – 7.8%). At the ‘day 0’ test, 14.6% (95% CI: 11.6–17.6%) of symptomatic close contacts tested positive compared with 5.2% (95% CI: 4.4–5.9%) of asymptomatic close contacts.

Conclusions

The application of additional symptom-based criteria for testing in this high-incidence population (close contacts) is of limited utility because of the low negative predictive value of absence of symptoms.