Delayed COVID-19 Testing Can Render Contact Tracing Ineffective, Says Lancet Study

According to researchers, a delay in COVID-19 testing can impair the effectiveness of contact tracing strategies in reducing the transmission of the disease

A study published in The Lancet Public Health journal warns that delays in testing for COVID-19 can affect the effectiveness of contact tracing strategies that is essential in curbing the spread of the coronavirus infection.

According to researchers, a delay in COVID-19 testing by three days or more post the development of symptoms by a patient can impair the effectiveness of even the most well-organized contact tracing strategy in reducing the transmission of the disease.

Speeding Up Testing Process

The study stressed that improving access to COVID-19 testing, combined with digital that minimizes tracing delays, will be key to the success of a contact tracing approach to reduce the spread of the virus.

"This study reinforces findings from other modeling studies, showing that contact tracing can be an effective intervention to prevent the spread of the SARS-CoV-2 virus, but only if the proportion of contacts traced is high and the process is fast," said study author Mirjam Kretzschmar from the University of Utrecht in the Netherlands.

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For example, the research team found that mobile apps can speed up the process of tracking down people who are potentially infected. To be successful, contact tracing measures must keep the rate of transmission of the virus, known as the Reproduction or R number, below one. This means that, on average, the number of individuals who will be infected by a single infected person must be less than one.

Contact Tracing Can Prevent Transmission

In the study, they used a mathematical model that reflects the various steps and delays in the contact tracing process. This enabled them to quantify how such delays affect the R number and the fraction of onward transmission cases that can be prevented for each diagnosed person.

The model assumes that around 40 percent of virus transmission occurs before a person develops symptoms. In the best-case scenario, the model predicts that contact tracing could reduce the number of people a person with COVID-19 passes the virus on to from 1.2 to 0.8.

For this to work, at least 80 percent of people who are eligible must be tested, there must be no delays in testing after the onset of symptoms and at least 80 percent of contacts must be identified on the same day as the test results are received.

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Duration Between Development of Symptoms and Testing

If testing is delayed by two days, keeping the R number below one would require contacts to be traced within a day and at least 80 percent of contacts must be identified, the model predicted.

The model assumes that conventional contact tracing takes a minimum of three days and is less efficient at tracking down contacts than mobile app technologies, which are assumed to be instantaneous.

Overall, the study found that reducing the time between a person developing symptoms and receiving a positive test result is the most important factor for improving contact tracing effectiveness.

(With inputs from agencies)

Related topics : Coronavirus