Money is dirty. It’s a perfect breeding ground for pathogenic bacteria, as revealed in research by Andreas Voss, Professor of Infection Control, who received the famous Ig Nobel Prize in Economics last week.

The Ig Nobel Prize is the ‘little sister’ of the genuine and prestigious Nobel prizes that will be announced in early October. Radboud University was earlier awarded Ig Nobel prizes in 2011 and 2015, including one for the universal nature of the word ’huh’. The Ig Nobel goes to research that first makes you laugh, and then makes you think.

In that respect, says Professor Voss over the phone, the prize is right up his alley. ‘I always use lots of humour in my teaching, before going on to convey a serious message.’

The medical microbiologist took to the stage last week during the ceremony at Harvard University in the United States. He wore a suit featuring a dollar design, a reference to one of the currencies investigated in his award-winning study.

The study dates back to 2013, but that is no barrier for eligibility for an Ig Nobel prize. Any noteworthy research, old or recent, can be nominated. Voss has no idea who put his name forward. ‘The prize came as a surprise to me too.’

What exactly did the study involve? Voss investigated how pathogenic bacteria survived on seven different banknotes. E. coli, which commonly occurs in faeces, was found to flourish on euro notes and Romanian leu banknotes, but not on the Indian rupee. Dollar bills, on the other hand, were an ideal breeding ground for MRSA, the dreaded ‘hospital bug’.

People who handle bank notes can therefore easily become infected. ‘The Romanian leu in particular was a disaster’, says Voss. So you should not be fooled about the country that you are in. ‘In India, you may think that the money is much dirtier than here, but in terms of bacterial growth, that’s not the case’.

High school paper

Like the Ig Nobel prize, Voss’ research initially started in a semi-serious fashion, he explains. ‘My son was looking for a topic for a paper in high school. I knew that at that time people in hospitals were very much focused on how a doctor’s tie or a nurse’s phone could transfer an infection. Then we thought: What about money?’ Together with his son and a Turkish researcher who had just started work, he went to drawers in his department and took some bank notes that were left over from conferences abroad.

The results did not end up in a high school paper, but they did appear in a scientific publication. Voss junior was the second author. ‘SGN Nijmegen’ was listed as his affiliation, the school that he attended at the time.

Central banks

The research had generated a lot of interest back then in 2013, Voss recalls. ‘All sorts of national central banks suddenly called me for advice about their bank notes – there must have been six or seven. Those phone calls will start up again now, ha ha.’ But he and his co-researchers actually have no idea what causes the differences between the currencies. In their article in the journal Antimicrobial Resistance & Infection Control, they speculated that it might have something to do with the material. Dollars are mainly made of cotton, and the Romanian leu of a plastic-type substance. ‘But we have never investigated that.’

Nevertheless, Voss is happy about the interest in this type of research. It shows how easily you can get an infection through contact with others. ‘Everything around us is infected, so you have to wash your hands properly whenever you to go to eat or cook, for instance. In hospitals, of course, that’s vitally important.’ For that matter, Voss is not unhappy with the current trend towards contactless payment, he chuckles. ‘Then you’re only dealing with your own bacteria, you don’t get any more from someone else.’