People worry about it, marry into it, kill for it and dedicate their whole lives to accumulate as much as possible. Also considered the root of all evil, we are of course talking about money. Humans have had a strong affinity for money and its history can be traced back to over 14, 000 years ago. There are a number of myths surrounding money with the most famous being that 4 in every 5 dollar bills in the US carries traces of cocaine. The myth has found to be true, not so much because of the extent of drug taking but how residues can be spread between notes by handling, ATM and counting machines. Although the myth is true it should be noted that the quantities of the drug ranges from parts per trillion to parts per billion.
Another enduring myth is that money can carry a diverse range of pathogens that can potentially make us ill. This was not always the case as our ancestors used the antimicrobial properties of money (silver, copper or gold) to disinfect water. The real problems occurred when paper currency was introduced in the 20th century. The first study of note was published in 1949 when Nisbet & Seoch highlighted the potential for money to be a vehicle for the transmission of clinically relevant pathogens. Since then there have been a number of articles and papers published on the microflora of money. In the main the “dirty money” stories have been fillers for slow news days or cater for germaphobes so it is timely to review what we currently know and to put the risk into prospective. There are actually three parts to the question the first being, are pathogens found on currency, can they survive and finally, can a potentially infective doses be transmitted.
Pathogens recovered from currency
From reported studies, the currency with the highest microbial loading is the UK at 4 log cfu per banknote. A recent study using next generation sequencing have identified 3000 types of bacteria present on US dollar bills but only 20% of the population could be actually identified. The majority of bacteria present were those commonly associated with skin with the occasional pathogen such as Staphylococcus aureus. The currency that has been found to harbor the highest prevalence of pathogens is the Romanian Liu with multi-drug resistant E. coli and Staphylococcus aureus being recovered. A further study evaluated the prevalence of pathogens or safety indicators on Iranian currency. It was reported that over 50% of the currency harbored E coli. Moreover, Salmonella, Listeria, Staphylococcus aureus, Yersina and Bacillus cereus was also recovered at a prevalence of 2-25% depending on the pathogen. For more exotic pathogen one only needs to visit Africa were pathogen protozoan, enteric viruses, mycotoxin producing moulds along with the traditional bacterial pathogens such as Staphylococcus aureus were recovered from banknotes.
A common link with studies is that pathogens had a tendency to be recovered from paper notes that had been in circulation for some time and sampled at food service outlets or clinical environments.
Survival of pathogens on banknotes
The survival of pathogens or their surrogates, has been found to be currency dependent with the Romanian Liu supporting the longest survival. Specifically, S. aureus and E. coli have been found to persist for over week on the currency. It has also been reported that the Romanian Liu is only one of a limited number of currencies that can support the growth of microbes provided the humidity is high.
For other currencies there is a relatively rapid die-off of pathogens due to desiccation although viable cells could still be recovered after 48h. Dormant microbes, such as Cryptosporidium, have longer persistent with flu viruses retaining infectivity for 17 days. Paper currencies have been correlated to extended persistence with the new polymer notes supporting less adherence and survival of microbes.
Transfer of microbes from banknotes to hands
The final part of the transmission process is the transfer of microbes from banknotes to fingertips then finally the food item. Yet again, the Romanian Liu leads the way as being the currency that facilitates the highest transfer of microbes to fingertips which is closely followed by the US dollar. In comparison, European banknotes have a lower degree of transmission to fingertips. As one may expect, moist fingertips acquired a higher level of microbes from banknotes compared to when dry.
Based on the available data one certainly would recommend washing hands after handling cash in food service outlets or clinical settings. Here, the risk of transferring pathogens can be considered high and the time between different handlers low. Even in everyday life it might be prudent to wash hands after handling currency especially when visiting Romania by all accounts.
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