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Tuesday, August 16, 2022

Explained: How to test your smartphone screen for coronavirus

Novel method involves collecting samples from smartphone screen and subjecting them to regular PCR testing. A double-blind study has found the non-invasive, low-cost test as accurate as regular PCR tests.

Written by Kabir Firaque , Edited by Explained Desk | New Delhi |
Updated: June 30, 2021 8:38:21 am
University College London researchers carried out the study at Diagnosis Biotech, a Chilean start-up headed by lead author Dr Rodrigo Young. (Credit: Diagnosis Biotech via UCL)

Scientists have developed a novel method for coronavirus testing that swabs your smartphone screen rather than your nose or throat. Compared to regular PCR testing, the Phone Screen Testing (PoST) method is non-invasive, costs less, and is equally accurate, the scientists have reported in the journal eLife.

Why smartphones

When people cough, sneeze or talk, they expel droplets that settle on surfaces around them. If a person is infected with SARS-CoV-2, these droplets will carry the virus. Previous studies have shown that SARS-CoV-2 can be detected from various kinds of surfaces, including their phones.

“Smartphones are personal objects that are constantly exposed to people’s mouths, their screens becoming a likely contaminated surface. Therefore, we hypothesised that Covid-19 contagious individuals will regularly deposit aerosols, droplets of saliva, or upper respiratory tract secretions containing shed SARS-CoV-2 virions, over the screen of their phone, which could then be sampled and detected by RT-PCR,” the authors write.

The study was led by Dr Rodrigo Young of University College London. The UCL team carried out the study at Diagnosis Biotech, a Chilean start-up headed by Dr Young.

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How it’s done

PoST involves collecting samples from the phone screen with regular swabs like the ones used for nasopharyngeal sampling, but embedding them in a saline water solution. “The sample is then subjected to a regular PCR like for clinical samples,” Dr Young said, by email.

The study was performed on 540 individuals in double-blind conditions who underwent both PoST and regular PCR testing. The two tests were carried out in different laboratories by independent teams, who were not aware of each other’s outcomes.



PoST detected the virus on the phones of 81.3% to 100% of contagious people with a high viral load.

Of the 540 individuals, 51 tested positive for SARS-CoV-2 in RT-PCR done on nasal/throat swab samples. Of these samples, 15 had a low Ct value (under 20) — and these also tested positive in PoST. This suggests that the ability of PoST to correctly identify positive individuals (sensitivity) is 100% in individuals with high viral load, the authors said. For 29 other samples with medium Ct values (below 30), the sensitivity of PoST was 89.7%.

The overall ability of PoST to correctly identify a negative case (specificity) was found to be 98.8%. Six samples were identified as positive in PoSt but negative in the clinical swab tests. While these could be interpreted as false-positives, the study notes that two of these individuals had Covid-19 symptoms, and suggests that these two results could also be false-negatives from the regular PCR tests.


Why it’s significant

The authors have pitched PoST as an option for large-scale testing. They note that regular large-scale testing is difficult because accurate tests are either too invasive, expensive, or complicated to implement.

“The important thing to take into account is that many people that are infected and contagious are not symptomatic. Therefore, they spread the virus without knowing,” Dr Young told The Indian Express. “… If we manage to do periodic mass testing (on) all people with no symptoms we could theoretically end the pandemic.”

A machine is currently under development by Diagnosis Biotech, Dr Young’s start-up. According to the UCL website, the machine will build on this research, taking a phone for PoST sampling, and deliver the results directly via SMS to minimise contact.

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First published on: 25-06-2021 at 06:09:51 pm
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