Our money is dirty. Over a hundred scientific studies have assessed the presence of microorganisms on banknotes, and there is a lot to research. Bacteria seem to love money, especially cotton-based bills. Scientists at Oxford University discovered that the average Bank of England note is home to 18,200 bacteria.
Because of the way we use cash, money has even been called the ultimate fomite for its ability to carry infection. Banknotes change hands frequently, but we rarely clean or sanitise them. If you are travelling in countries with poor hygiene standards and handle paper money, remember to wash your hands often!
Much of the research has focused on bacteria such as Salmonella, Listeria, and E. coli, as these can cause food poisoning. However, the survival of human influenza viruses on banknotes has also been studied. Researchers in Switzerland discovered that infectious viruses can survive for several days on banknotes, especially in the presence of even a tiny amount of mucus.
Mucus and other airway secretions expelled when a person with the flu coughs or exhales appear to protect the virus when it becomes airborne.
In response to the novel coronavirus disease, or COVID-19, China in February 2020 announced that it is disinfecting and isolating used banknotes to stop the spread of the SARS-CoV-2 virus (previously called 2019-nCoV).