Testing your mobile phone for Covid-19

Mobile phones have proved to be a powerful instrument in the fight against the coronavirus pandemic, whether it’s running apps to track contacts between people, or providing portable digital vaccination passports in some jurisdictions. Now mobile phones might be about to help us cut the cost and increase the uptake of Covid-19 mass screening: it turns out that swabbing a phone is nearly as good as swabbing the owner for infection. Speaking with Chris Smith, UCL’s Rodrigo Young explains how he came up with the idea...

Rod - What I was puzzled about was the fact that testing was so essential at the beginning of the pandemic, but at the same time, it was very invasive and also very expensive. So, it was difficult to test mass populations, which is what we needed. So some people say if we would have tested everybody every week for two months, the pandemic would be over, but we couldn't do that because it was too expensive. It was not feasible at a large scale. So I thought, how can we do this? How can we find a way to make it approachable to people? And also cheaper. That's how I came up with this idea.

Chris - And what is that idea?

Rod - Clinical PCRs are expensive because the samples taken from a person, the whole progression of that sample through the pipeline is through clinical standards, which are quite high and very expensive. You could do the same thing using reagents that have the same quality, but don't have the certification to be clinical and you could make it much cheaper. So I thought, why not using a sample that is like a readout from that person? So I thought the mobile phone is the device that we're touching and we're speaking to most of the time, there could be a very tight correlation between what we find in people's nose and mouth to what there is on the screen of mobile phones.

Chris - I suppose that's logical because of course the one place the phone does go apart from your hand is up against your face and in front of your mouth.

Rod - Absolutely. And by that time, there was a lot of evidence that SARS-Cov-2 could be detected on surfaces. So what I did was very simple. I just gathered a group of people that had been diagnosed with COVID within two days and I swabbed their phone and I did a PCR and 10 out of 10 were positive. So we then did a big study, over a thousand people, of those people that had a clinical diagnosis with a very high viral load. We were able to detect almost all of them. Now, those that were positive for COVID, but had low viral load, so they're not as contagious, those we didn't detect, which makes sense because those with a low viral load are not expelling or shedding the virus.

Chris - So this would put you sort of on par with the performance of the lateral flow tests that we've been using in some respects then, which tend to be pretty good at picking up people who are at their most infectious and less likely to pick up spurious, kind of tailenders who are probably not infectious anymore.

Rod - That's what we think. And we're doing a study comparing all three methods to see how they correspond to each other. We don't have big numbers, but so far the correlation is very, very high. It's nearly a hundred percent with lateral flow devices.

Chris - What are the implications of this? And is it that instead of subjecting people to what feels for some like a brain biopsy, which actually is arguably putting people off of getting screened, we could have a system where you run a swab over your mobile and send that off on a regular basis, and that would be as good?

Rod - That's exactly what we're doing in Chile. We're testing people that work in companies or production lines. We test them at the beginning of the week and you take out of the production line, people that test positive. This is like a prediagnostic test. So you have to confirm it with a nasal PCR and it's a much cheaper way of doing it. And it's not invasive. It's very quick to do, so, taking the sample takes around 40 seconds, less than 40 seconds.

Chris - One of the things that's frustrated our PCR tests that we've been doing, or members of the population, and particularly people who are coming into hospital is that if they've had coronavirus, they often test positive for extended periods of time afterwards. Now, do you have any feel for how the phone performs? So if a person is positive, how long does their phone stay positive? Is it fairly tightly linked to the genuine infectivity of that person? Or might their phone test positive like they might for weeks afterwards?

Rod - We have really, really interesting examples of that. In that, many times people finish their quarantine, get back to work, we test them and they're still positive. Some people when they keep on being positive on the phone, again, they're still positive on the nasal swab. And this is very frustrating for these people because they do their whole quarantine, they want to get back to work and back to normal life, but they can't because they're still shedding the virus.

Chris - Could this not backfire? In the sense that we know mobiles are mucky, and we know that they have, or they at least mirror people's microbiomes and they're covered in all kinds of horrible things. And we try and encourage people to clean their mobile phones as much as possible. Are you going to have to start discouraging people from cleaning their mobiles in order to test positive for COVID tests, with greater sensitivity and therefore potentially spread other things instead?

Rod - That was actually one of the interesting things of the study that we published in eLife. When we did this big validation study, we asked people if they had cleaned the screen of their mobile phone, but it seems that what people use to disinfect their phone might really disassemble the virus or kill the virus, but we're still able to detect the traces that are left behind. So the PCR technique is sensitive enough to still detect the traces that are left behind after you disinfect the phone.

Chris - You know, what's next for your initiative? You've got to design the app and the little gadget that will plug in the USB port on the bottom of the phone. So that the whole thing is an integrated portable screening system so that people could just plug it into their own phone and they won't even have to send you a swab.

Rod - That would be interesting, wouldn't it? What we're doing for now actually is designing a machine that will take samples from mobile phones. Like when you put a card inside an ATM, you can do the same thing with your phone. You put your phone into this machine, the machine takes a sample, and then after a few hours, you get your result as an SMS or text on your phone.