TORONTO - The people who coined the terms filthy lucre and dirty money may have been on to something.
Swiss researchers have reported that influenza viruses can survive - alive and potentially infectious - on bank notes for up to 17 days in some cases. It's not known what portion of influenza transmission is due to the touching of contaminated surfaces with hands which then transport viruses to the vulnerable mucous membranes of the nose or mouth. And this study can't answer that question.
But lead author Yves Thomas said Wednesday he believes the touching of contaminated surfaces plays a role in the spread of flu. And those contaminated surfaces can include folding money.
"When you see that the virus is still alive for several days, I can't imagine that it does not infect. I'm sure that it can infect," Thomas, a virologist at the Swiss National Centre for Influenza, said at a major international conference, Options for the Control of Influenza.
"It's still alive. And it's alive in quantities that can infect."
But a Toronto-based infectious diseases expert said she isn't convinced.
"The problem with all of the environmental studies of influenza and other pathogens is the fact that these bacteria and viruses survive in the environment doesn't mean they are transmitted by the environment," said Dr. Allison McGeer, head of infection control at Toronto's Mount Sinai Hospital.
"And while it sounds just counterintuitive to say that if the virus is there in the environment you can't catch it, there is in fact a substantial amount of epidemiological evidence that that's true."
McGeer said, for instance, that there's really no proof people who handle bank notes for a living suffer more bouts of the flu than those who don't.
"Now people will argue that maybe we haven't looked for it," she acknowledged.
"But the truth of the matter is that kids don't handle bank notes. But there's lots of evidence that infection rates are highest in children and children transmit the most. And influenza was transmitted pretty regularly before we had bank notes."
The work was done at the behest of Swiss National Bank, which provided the currency on which the testing was done.
Rising concern about the possibility of a flu pandemic had executives worried that bank notes might serve as a virus delivery system, both for bank employees who handle paper money, and for the broader public.
So the scientists inoculated small pieces of bills with several different strains of human influenza - an influenza B virus and three influenza A viruses. Two of the As were H3N2 viruses and the third was an H1N1.
They allowed the notes to dry naturally, and kept them at room temperature (22 C). At various points they submerged pieces of the notes in a medium, then tried to see if the medium contained live viruses by putting it into culture to see if virus would grow.
The H1N1 and influenza B viruses didn't last long on the money, dying within an hour or so. But one of the H3N2 viruses survived about 24 hours and another was viable up to 72 hours, Thomas said.
The team then decided to try to see if mucus would enhance survival. They mixed the viruses with mucus and swabbed a thin slick of the stuff on bank notes.
The difference in survival time was substantial. "With secretory mucus, it's 17 days," Thomas said.
As with the first round of the work, the survival time varied depending on the subtype of virus, with 17 days being the longest period for which virus was viable. The influenza B virus, for instance, lasted 24 hours in mucus but only two hours without it.
The mucus may keep the virus from drying out, Thomas suggested, noting another scientist ventured the view that the protein in the mucus may play some role in the extended survival time.
But laboratory experiments, done under controlled conditions, don't always reflect what happens in the real world.
So the group tried a third phase of the work, swabbing still more bills with "nasopharyngeal secretions" - yes, that's snot - from 14 flu-infected children.
At 24 hours, live viruses were retrieved from 50 per cent of the bills. At 48 hours, there was live virus found on 30 per cent.
Thomas said he believes that depending on the virus used, the survival in mucus ranges from about two to 17 days, and is probably closer to the lower end of that spectrum.
"I think in real life maybe we are more in (the range of) several days," he said.
Still, it has him thinking about what money he would use during a pandemic? "My credit card, maybe," he said with a laugh.
