Washing our hands before eating and after going to the bathroom; does it end here? Let’s talk about money.
This time we will discuss a third situation in which we should consider our hygiene: handling money. Banknotes and coins are fomites* usually exchanged for goods and services. They pass through the hands of people with differing health and hygienic standards. Furthermore, while not in use they remain in a variety of environments and
* Wikipedia: A fomes or fomite is any nonliving object or substance capable of carrying infectious organisms, such as viruses or bacteria, and hence transferring them from one individual to another.
As the definition of the fomite indicates, the money offers a surface that all kinds of microorganisms (infectious or not) can take advantage of. Specifically, the currency notes are considered vectors of transmission of pathogenic microorganisms. We can imagine money as a cruise constantly sailing, letting go, and picking passengers wherever it moves. As a curiosity, it has been proven that the age and manufacturing material of notes are strongly correlated to the total amount of microorganisms they contain.
The number of folds in a note can be used to approximate its time in circulation (in case the information can not be obtained with the serial number). Interestingly, each year in circulation is associated to a fold in the note. Also, for each 2-3 folds in a note, the bacterial concentration appears to increase by an order of magnitude (x10). Studies focusing in the DNA of the notes reported that eukarya is the most abundant group in the note surface (fungi, metazooa parasites, skin scaling cells of people and dogs …), followed by bacteria, viruses and archaea in the last place.
Bills made with cotton tend to carry more microorganisms than those made with polymers. Basically, cotton micro-fibers are more absorbent and also provide more surface where microorganisms can be deposited. On the other hand, although the notes made with polymers have a smoother surface, they are more resistant and endure more time in circulation, therefore, accumulating more microorganisms throughout their useful life.
A recent study has demonstrated the ability of cotton-based notes to retain attached bacteria even after 30 successive washes (see next figure). The same work shows another interesting fact: Metal elements in coins such as copper, aluminum and nickel inhibit the growth of pathogens such as Staphylococcus aureus.
How far to worry about?
Although the majority of microorganisms are not to be feared, a great diversity of pathogens and parasites has been isolated from notes. The 5 most frequent are Escherichia coli, Bacillus sp, Staphylococcus aureus, Coagulase negative Staphylococci and Salmonella. The list goes on for those who are interested. Although many pathogens are found, the cultivation of these is generally possible only after enrichment. While for now they do not pose a serious threat to human health, do not forget that pathogens are always waiting for an opportunity!
Prevention and recommendations
The recommended measures in environments where food is handled are those that most governments already make public:
- Money and food should be handled by different workers.
- Alternatively, it is recommended to use one hand to touch the money and the other (with glove) to manipulate food.
- If these recommendations can not be fulfilled, hands must be washed after each transaction.
References for more information:
Filthy lucre: A metagenomic pilot study of microbes found on circulating currency in New York City (2017). Maritz JM, Sullivan SA, Prill RJ, Aksoy E, Scheid P, Carlton JM.
Dirty Money: A Matter of Bacterial Survival, Adherence, and Toxicity (2016). Vriesekoop F, Chen J, Oldaker J, Besnard F, Smith R, Leversha W, Smith-Arnold C, Worrall J, Rufray E, Yuan Q, Liang H, Scannell A and Russel C.
Paper money and coins as potential vectors of transmissible disease (2014). Angelakis E, Azhar EI, Bibi F, Yasir M, Al-Ghamdi AK, Ashshi AM, Elshemi AG, Raoult D.