To find traces of SARS-CoV-2 on your phone, we pass a sterile swab over the screen to capture any virus particles. We then analyse the liquid in which we store the swab by PCR in our lab. A positive result means that the owner of the phone is likely in the contagious phase, which must be confirmed by a clinical nasopharyngeal PCR.

The smartphone is one of the devices that we use the most, on average, 3 to 5 hours a day. This allows us to find traces of the virus on the screen when we are infected and spreading SARS-CoV-2.

The PCR technique we use for PoST directly detects the presence of SARS-CoV-2 in samples when the person is ill. Unlike PCR, the lateral flow test detects the antibodies that our body generates as part of the immune response to the infection. The production of antibodies takes at least a week, so you can have a negative lateral flow test result even if you are contagious for days. Furthermore, antibodies remain circulating in the blood for months, so you can be already healthy and still test positive by rapid test.

Our data shows that Phone Screen Testing (PoST) has a sensitivity of between 81.3% and 100% for cases with high viral loads, that is, those with the highest probability of being contagious. The study we developed in collaboration with clinics and universities in Chile and London compared the results of the PoST with those of the nasopharyngeal PCR performed in the clinic on the same people.

If you are sick with COVID-19 and have a low viral load, it is likely you are not infectious anymore but will still test positive by nasopharyngeal PCR. The Phone Screen Testing mainly detects traces of SARS-CoV-2 in the smartphones of people with high viral loads. Therefore, despite testing positive by nasopharyngeal PCR, we will not find traces of the virus on the screen of your phone if you have a low viral load.

The probability is extremely low, but it can happen. For example, your smartphone may have been repeatedly used by someone infected with SARS-CoV-2.

Yes, there are no fail-proof techniques, and Phone Screen Testing is no exception. In our studies, the specificity (negative COVID-19 individuals identified as negative by PoST), was between over 98.8%. Therefore, the probability of a false negative is less than 1.8%.