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Pathogen contamination of touch screens poses a potential health danger

Cleaning is ineffective, so is touchless technology the only solution?

We have all become more aware of passing on diseases through touch, coughing, sneezing, and even talking and breathing during the pandemic. We have also learned the importance of R values- or reproduction number – the average number of people an infected person will subsequently infect.

We will look at one vector involved in disease transmission, public touch screen user interfaces (TUIs). In the modern world, these are ubiquitous and commonly found in stores, hospitals, doctors surgeries, petrol pumps, reception areas, etc.

Even in normal non-pandemic times, public TUIs are likely to be infected by many bacterial and viral pathogens. We cite some recent commentary that highlights this. But in reality, how dangerous are they? To examine this, we review recent research on modelling TUI-related pathogen infection in some depth, demonstrating that the dangers are genuine.

We also look at some mitigating measures that may not be as effective as they first appear. For instance, effectively decontaminating a TUI requires hundreds of cleans a day.

The most effective way to eliminate these risks is to replace TUIs entirely with touchless technologies. While various solutions have been proposed, we believe the most effective is a touchless intelligent voice recognition system, of which Indigo is a market leader.

Public touch screens are almost always contaminated with pathogens

There is ample evidence regarding contamination of shared touchscreens. For instance, the Healthline article Want to Avoid Dangerous Bacteria? Don't Use Public Touch Screens" pointed out that about 253,857 colony-forming units per square inch of bacteria on average are found on airport check-in screens. These pathogens originate from people's intestines, gut, nose, mouth, throat, and faeces.

Similar contamination has been found on touch screens in hospitals and grocery stores. One of the most common is Enterococcus faecalis, (E. faecalis) which can cause fever, fatigue, headache, chills, vomiting, and diarrhoea. It can also result in meningitis and urinary tract infections.

Often E. faecalis is introduced by people failing to wash their hands properly after going to the toilet.

Staphylococcus is frequently found on public touchscreens. While it doesn't cause illness in the person carrying it can result in others getting septicaemia, pneumonia, toxic shock syndrome, and food poisoning. Likewise, listeria has been found on restaurant touch screens and can be the source of food poisoning, miscarriages and stillbirths.

According to the article, our only defence against these dangerous pathogens is frequent hand washing and sanitisation.

An equally disturbing though somewhat sensationalised article, "Traces Of Poo Have Been Found on Every McDonald's Touchscreen", reported that each self-serve touchscreen tested was contaminated with faeces derived bacteria, including Staphylococcus and E. faecalis.

Taking a more measured approach, the Washington Post argues that while "McDonald's touch screens are not contaminated with poop", there are a lot of bacteria; however, it claimed that healthy people are unlikely to be harmed by them. It also published a statement by McDonald's that.

"Our self-order screens are cleaned frequently throughout the day with a sanitiser solution. All of our restaurants also provide facilities for customers to wash their hands before eating."

However, as we later point out, to maintain a safe interface, such screens would need to be cleaned hundreds of times a day, which of course they are not, and as we also point out below, 30% of people fail to wash their hands properly after visiting the toilet.

How effective is handwashing?

In the early days of the Covid-19 pandemic, we heard a great deal about the importance of handwashing. However, a Korean study of the effectiveness of handwashing found that 30% of individuals do not wash their hands adequately after using the toilet.

There are also additional issues, including contaminated soap and doorknobs. Viral loads in faeces may be up to 108 PFU/g with bacteria found on hands of 0.85 105CFU for washed and dried hands and 3.64 105CFU for unwashed hands.

How harmful are these bacteria?

Given that, in all likelihood, any public touchscreens you may come across is likely to be contaminated, how worried should you be that touching it might make you ill?

In their 2020 paper "Modelling disease transmission from touchscreen user interfaces" Andrew Di Battista and his colleagues investigated human-fomite interaction on touchscreen interfaces. They pointed out that while touchscreens carry pathogens, the question is if they can pass on sufficient numbers of them to cause disease in others. Also, if this is so which diseases, and whether it is due to an isolated touch user interface (TUI) event or by multiple users' interactions through an interaction network of users.

The researchers used stochastic Monte-Carlo simulations to establish the fundamental mathematical parameters of fomite-mediated disease transmission and how they affect outcomes. Another aim of their research was to examine the impact of various touchless technologies and compare their effectiveness with frequent touch surface cleaning and disinfection.

Model and parameters of touch surface transmission

For disease transmission to occur:

  1. An infectious doner must interact with the fomite and deposit some of it on the touchscreen surface
  2. The fomite must survive long enough for an infections amount to be picked up by a new host
  3. The newly exposed person must transfer the pathogen to the eyes, mouth or nose

A full description of the model and pseudo-code for their algorithm is available in the original paper. Essentially it is based on queuing theory and stochastic Monte-Carlo simulations, though we are mainly concerned with their results which we will now summarise.

The simulations were designed to determine the following:

  • The probability of becoming infected after using a TUI
  • The number of susceptible individuals becoming infected by a single infectious user over a day
  • The time gap between infectious and infected
  • The efficacy of frequent cleaning on reducing the probability of infection


The researchers used a pseudo-reproduction number R which they defined as the number of susceptible people infected by the fomite after an infectious person has contaminated them. During the pandemic, we learned that reducing the R number to less than 1.0 was critical, but that is a very different situation from transmitting diseases via a TUI. In the latter case, the R number should be significantly lower than 1.0.

The simulations indicated that timing plays a crucial role in the number of infections, as does the number of TUIs per location, pathogen survival time, and the rate of TUI use, all very much as you might anticipate. Susceptible users who immediately follow an infectious user are most at risk. High touch rates effectively clean the TUI; the following susceptible user will become infected while simultaneously shielding subsequent users.

Mitigating measures

Possible ways to maintain low infection levels include compulsory handwashing, effective against pandemics in airports.

Alternatively, TUI operators can employ enhanced sterilisation regimens. However, to significantly affect the R value, each TUI would need to be cleaned hundreds of times a day, which may be prohibitively costly. There is also a risk associated with cleaning agents used.

UV light can replace chemical disinfectants but doesn't change the number of cleans required and carries a health risk.

Self-cleaning, antimicrobial surface coatings are available, but they are not effective against all pathogens, and their antimicrobial properties could fall with regular use.

An alternative solution is touch-free interfaces. These remove the need to touch, thus eliminating depositing and picking up pathogens from surfaces.

Indigo replaces TUIs with intelligent voice and face recognition

While several alternative technologies aim to replace TUIs with more hygienic solutions, Indigo is one of the most innovative and intuitive. The Indigo system integrates voice and face recognition software to create an intelligent interface that is typically deployed as a digital receptionist.

The Indigo solution is also multi-talented. For instance, It can respond to your customer or visitors' requests, engage them in meaningful dialogue, communicate with staff, and undertake many additional tasks. Moreover, as it is entirely contactless, there is zero risk of pathogen transmission.

The bottom line is that shared TUIs can no longer be considered a safe, hygienic solution. Handwashing, screen cleaning and sanitation provide at best a slightly reduced risk; they certainly don't eliminate the threat. So TUI technology will inevitably need to be replaced with something better. Indigo is available currently, so why not take a closer look?

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