Further evidence of SARS-CoV-2’sample pool ‘helps improve test capabilities

One of the problems facing health authorities today is that asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can still get the virus. Therefore, testing as many people as possible is important for immediate isolation of cases to prevent the virus from spreading further.

Testing is still a major problem in many countries due to the lack of test kits and equipment. Now, a team of German scientists have developed a new method to improve the test capabilities of coronaviruses.

Research published in journals Lancet infection, Countries are emphasizing the development of procedures that can enhance coronavirus testing capacity to meet the high demand for testing. Mass tests are essential for early identification and isolation of asymptomatic people.

Researchers Virology Institute at Saarland University Medical Center in Homburg, Germany proposes a pool of samples prior to RNA Reverse Transcription Polymerase Chain Reaction (RT-PCR test). When a sample in a group returns positive, it is the only time people need to be individually screened. This pooling approach reduces the number of tests required and therefore the test kits.

What is a pool test?

Pool tests are a way to detect viruses in a combined sample for faster results. This method maximizes resources and allows more people to test the virus. For example, swab samples taken from the nose or throat are mixed with buffer and tested for the presence of SARS-CoV-2.

If a group of samples is virus positive, it is when they retest each sample to see which one gave a positive result. In this study, the team investigated viral load during symptomatic infections with the novel coronavirus and determined the effect of sample pools on RT-PCR sensitivity.

To do this, they compared the cycle threshold (Ct) values ​​of pools that were positive with the Ct values ​​of individual samples tested as positive. They isolated RNA from cotton swabs using a device called the Nucli Sens easy MAG. Since mid-March they have been using treatment at the Saarland University Hospital to protect vulnerable patients from infections, especially from those who are unaware that they are infected.

Since the screening method proved successful, it has been used to screen residents and staff in local care homes.

“To protect these groups at high risk of death from coronaviruses, we need to prevent the entry of viruses from asymptomatic individuals, including the care and care staff who care for them. A high group includes inpatients with chronic illnesses, such as those with cardiovascular disease and cancer, the elderly, and especially residents of nursing homes and housing facilities. Can only be used to identify asymptomatic contacts and thereby prevent infection of the most vulnerable people. ”

Test kit savings

As many countries are working on coronavirus pandemics, the new procedure will help reduce the demand for test kits. Launching tests in many countries is important to prevent the rapid spread of the virus, and many countries are now blocked for months.

In this study, the researchers found that generating a pool of 30 samples from 3 subpools of 10 samples could reduce retesting. Also, if the large pool turns out to be positive, the three subpools are re-analyzed and then the individual samples.

When they analyzed the results of the pooled test method from March 13 to 21, they found that 267 tests out of 1,191 samples were sufficient and detected 23 positives.

Researchers have suggested that pooling up to 30 samples per pool can also improve test capabilities on existing equipment and test kits. In addition, pooled tests can be used on asymptomatic carriers to detect positive samples with sufficient diagnostic power.

“It should be mentioned that single borderline positive samples may escape detection in large pools. These samples are usually conserved 14 to 21 days after symptomatic infection. As seen by patients, pool sizes can accommodate a variety of infection scenarios and can be optimized according to infrastructure constraints, ”the team wrote.

Since the team began using this method in hospitals, it is now being used to screen residents of 131 nursing homes and home care facilities in Saarland, where most patients are vulnerable. Testing at these facilities will help protect the elderly population at highest risk from COVID-19 infections. An estimated 22,000 people will be tested.

“We also received a number of urgent inquiries from hospitals in Germany and abroad because limiting test capacity proved to be an important issue at this time,” Smola added.