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

In a recent study published on medRxiv* preprint server, researchers assessed the impact of a delay in contact tracing of coronavirus disease 2019 (COVID-19) cases on the health outcomes of transmissions, hospitalizations and deaths from the syndrome coronavirus severe acute respiratory tract 2 (SARS-CoV-2) in England.

Study: To assess the impact on health outcomes of an event that caused a delay in contact tracing of COVID-19 cases. Image Credit: bob boz / Shutterstock

Contact tracing has played a central role in assessing the general population’s health responses to SARS-CoV-2 and involves identifying contacts of SARS-CoV-2 positive individuals and advising them on treatment. self-isolation to reduce transmission of SARS-CoV-2.

As of September 2020, 15,861 COVID-19 case records from the Second Generation Laboratory Surveillance System (SGSS) were not uploaded to the Contact Tracing Advisory Service (CTAS) data tool and by subsequently delayed contact tracing of COVID-19 cases.

SGSS records contain demographic and diagnostic information from laboratory test reports for patients who tested positive for SARS-CoV-2, while CTAS records represent SARS-CoV-2 case episodes, including including information on the movements of cases during their infectious 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 effect of delayed contact tracing of COVID-19 cases on transmission of the virus. SARS-CoV-2, hospitalizations and deaths in England. .

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

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). surname, first name and postal code.

The CTAS dataset included the main cases that were affected by the event and these cases were called the “lagging group”, while the main cases belonging to the same period (between September 30 and October 5 2020) were not affected by the event included the “control group”.

Graphs depicting the time taken to initiate and complete contact tracing of cases and contacts in the lag and control groups

Graphs depicting the time taken to initiate and complete contact tracing of cases and contacts in the lag and control groups

Secondary cases were described as people who reported contact with a primary case and people who had contact with a primary case between day 2 and day 14 after symptom onset or test date among secondary cases.

In addition, the contact datasets have been linked to the UKHSA hospital-based COVID-19 dataset, which was extracted on November 22, 2021, and pulls daily data from two national datasets , namely the Secondary Uses Services (SUS) data set and the Urgent Care data. Set (ECDS) describing patient hospitalizations and use of emergency care services, respectively.

Primary outcomes included secondary attack rates (SAR), hospitalizations, and deaths among primary contacts and secondary contacts compared with concurrent and unaffected cases.


A total of 15,861 SGSS records were detected as affected by the event, of which 98% (15,467) matched CTAS records. After data cleaning, 96% (15,285) of the primary cases affected by the delay were eligible for analysis. The control group comprised 43,742 concurrent primary contact cases, including all CTAS records in the aforementioned time period not affected by the event.

Initiation of contact tracing was delayed by three days in primary contact cases among the late group compared to controls, associated with incomplete contact tracing of primary cases among individuals in the late group (80%) and controls (83%).

The delay increased viral transmission to non-household contacts. SARs among non-household contacts were higher among secondary contacts (7.9%) in the late group compared to controls (5.9%). Among secondary contacts, there were no statistically significant differences between individuals in the delayed group and controls with respect to hospitalization (crude odds ratio 1) and death (crude odds ratio 0.7).

Globally, the results of the study revealed that the delay in contact tracing for COVID-19 cases slightly affected their health.

*Important Notice

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

Journal reference:

  • Assessing the Impact on Health Outcomes of an Event Leading to 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 2022 preprint, DOI: /2022.05.19.22275053v1