Cash may be more filthy and disgusting than you thought, according to new research.
Ordinary bank notes, such as dollar bills, can harbor harmful varieties of bacteria, and could be an effective medium for spreading infectious diseases among people, said a group of Hong Kong researchers in a study published this week in the journal Frontiers in Microbiology.
The team said the research can help inform the mechanisms by which infectious diseases and antibiotic resistance spread throughout the world. Hong Kong has seen outbreaks of several diseases since at least the 1960s, including an influenza pandemic in 1968, avian flu in 1997, SARS in 2003, and a swine flu outbreak in 2009.
Currency is possibly one of the main media transmitting pathogens and drug resistance due to its wide circulation in daily life," said a team of researchers hailing from the University of Hong Kong, the Guangzhou Center for Disease Control in China, and Germany's Leibniz Institute for Natural Product Research and Infection Biology.
Given the relatively high risk of pandemics in crowded, cosmopolitan cities with humid climates, like Hong Kong, the researchers said in their study that "it is of clinical importance to examine whether HK banknotes could serve as pathogen reservoirs and vehicles through which pathogenic bacteria and infectious diseases could be transmitted to humans."
The team collected HK $20 notes from cashiers at 12 hospitals and three metro stations throughout Hong Kong and scraped the bills for bacteria samples.
They found that ordinary cash is quite hospitable to bacteria, more than a third of which were potentially pathogenic species, including the well-known and potentially deadly E. coli and V. cholerae (the bacteria that cause cholera).
"In short, banknotes act as a medium 'absorbing' bacteria from other environments and the potential pathogens live quite well on the banknote surface," said study co-author Jun Li, a researcher from the University of Hong Kong, in a news release.
In particular, currency had a wider diversity of bacteria than samples taken from people's hands, drinking water, marine sediment, and the air in metro stations. They also had a higher chance of having bacteria with antibiotic-resistant genes.
Li said this means the bacteria from cash could be contributing to resistance to the antibiotics that fight bacterial infections.
"The most important recommendation we could raise is that before a cashless society develops, the banks and government should pay extra attention to the hygiene problem of the currency, which is still frequently used in our daily life," Li said, in the release. "We recommend some routine disinfection of the currency from the bank, some public service ads reminding people to pay attention to wash the hands after touching currencies and the promotion of more electronic payment service, like mobile payment. We particularly would like to see the politicians and policy-makers inspired by this study."
Watch: Bathing in bacteria?