The impact of delayed COVID-19 contact tracing on health outcomes

In a recently published study medRxiv* Preprint Server, Researchers assessed the impact of a delay in contact tracing of 2019 coronavirus disease (COVID-19) cases on the health outcomes of transmission, hospitalization and death of severe acute respiratory syndrome coronavirus 2 (SARS-CoV- 2) in England.

Study: Assessing the health outcome impact of an event that caused a delay in contact tracing of COVID-19 cases. Credit: bob boz/Shutterstock

Contact tracing has been critical in assessing general population health responses to SARS-CoV-2 and includes identifying contacts of SARS-CoV-2 positive individuals and providing advice on self-isolation to reduce SARS-CoV-2 transmission to reduce.

In September 2020, 15,861 Second Generation Laboratory Surveillance System (SGSS) COVID-19 case records failed to upload to the Contact Tracing Advisory Service (CTAS) data tool, subsequently delaying the tracing of COVID-19 case contacts.

SGSS records contain demographic and diagnostic information from laboratory test reports for patients who tested positive for SARS-CoV-2, while CTAS records present SARS-CoV-2 case episodes, including information about the movements of cases during their infection period, their contacts , and demographic and clinical characteristics.

About the study

In the present observational study, researchers from the UK Health Security Agency, the University of Bristol and the University of Cambridge assessed the impact of a delay in contact tracing of COVID-19 cases on SARS-CoV-2 transmission, hospitalizations and deaths in England.

The UK Health Security Agency (UKHSA) provided the SGSS records which were cross-checked with the CTAS records to validate the cases affected by the event and subsequent contacts and cases were identified. The study used CTAS data from SARS-CoV-2 positive individuals and their contacts for the analysis.

The matching was done in multiple rounds based on combinations of identifiers such as the National Health Service (NHS) number. SGSS Unique Identifier, Date of Birth (DOB). First name, last name and zip code.

The CTAS dataset included the primary cases affected by the event and these cases were referred to as the “delay group”, while the primary cases belonging to the same period (between September 30 and October 5, 2020) were not affected event included the ‘control group.

Charts describing the time it takes to initiate and complete contact tracing of cases and contacts in the delay and control groups

Charts describing the time it takes to initiate and complete contact tracing of cases and contacts in the delay and control groups

Secondary cases were described as people who had reported contact with a primary case subject and people who had contact with a primary case between day 2 and day 14 after onset of symptoms or the test date, among the secondary case subjects.

In addition, the contact records have been linked to the UKHSA Hospital Onset COVID-19 dataset, extracted on 22 November 2021, which pulls daily data from two national datasets, namely the Secondary Uses Services (SUS) dataset and the Emergency Care dataset Set (ECDS) describing hospital stays of patients or the use of emergency services.

The primary outcome measures included secondary attack rates (SARs), hospitalizations, and deaths for primary contacts and secondary contacts compared to concurrent and unaffected cases.


A total of 15,861 SGSS records were identified as affected by the event, of which 98% (15,467) matched the CTAS records. After data cleansing, 96% (15,285) of the primary cases affected by the delay were eligible for analysis. The control group consisted of 43,742 concurrent primary contact cases, including all CTAS recordings within the above time period that were unaffected by the event.

The start of contact tracing was delayed by three days in the primary contact cases in the lag group compared to the controls, which is associated with incomplete contact tracing of the primary cases in the lag group (80%) and controls (83%). .

The delay increased virus transmission to contacts outside the household. The SARs for contacts outside the home were higher for the secondary contacts (7.9%) in the delay group than for the controls (5.9%). For the secondary contacts, there were no statistically significant differences between the people in the delay group and the controls with regard to hospitalization (raw odds ratio 1) and death (raw odds ratio 0.7).

In total, The study results showed that the delay in contact tracing for the COVID-19 cases slightly impacted their health.

*Important NOTE

medRxiv publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health behavior or treated as established information.

Magazine reference:

  • Assessing the health impact of an event that caused a delay in contact tracing of COVID-19 cases, Lucy Findlater, Livia Pierotti, Charlie Turner, Adrian Wensley, Cong Chen, Shaun Seaman, Pantelis Samartsidis, Andre Charlett, Charlotte Anderson , Gareth Hughes, Matt Hickman, Obaghe Edeghere, Isabel Oliver, medRxiv Preprint 2022, DOI:

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