Nothing like a few diseases to give rise to a whole new class of products proclaiming that “they” will kill 99.9% of common bacteria, viruses and fungi. This includes everything from hand-sanitizing liquids to products like computer keyboard and shopping cart tissues. However, they often are based on laboratory tests that don’t represent the imperfections of real-world use. Human subjects, or countertops, in labs are usually cleaned first, then covered on the surface with a target bug. That is of course a far cry from a typical kitchen counter or a pair of human hands.

Jason Tetro, a microbiologist at the University of Ottawa showed the difference by testing three hand-sanitizer products for CBC News last month among eighth graders in Hamilton, Ontario. Three popular sanitizers killed between 46% and 60% of microbes on the students’ hands, far short of 99.99%. Bugs that aren’t killed by sanitizers aren’t necessarily more dangerous than those that are. But the more that remain, the greater the chance of infection, doctors say.

The companies whose products were evaluated responded that those lab tests are what health regulators require. “Real-world application is completely subject to interpretation,” says Jay Beckman, head of sales for MGS Soapopular Inc., the U.S. distributor of Soapopular, one of the products tested. “Nothing is guaranteed.”

Soap can be effective, but human nature can stand in the way. In a now famous study Navy recruits (1996 – 1998) were directed by their commanding officers to wash their hands at least five times a day. That and other measures helped reduce outpatient doctor visits for respiratory illness by an impressive 45%. (http://linkinghub.elsevier.com/retrieve/pii/S0749379701003233)

Civilians, lacking a commanding officer to direct them, can be a bit more problematic hand washers. Most, left to their own devices, don’t scrub the required time to achieve clean hands (20 seconds).

twinkle twinkle
CDC recommends singing Twinkle, Twinkle Little Star or "Happy Birthday" twice to achieve that 20-second goal.

To cite a 99.9% fatality rate, manufacturers don’t have to kill 99.9% of all known bugs. Regulations don’t require them to disclose which bugs they exterminate, just that the products are effective against a representative sample of microbes. For instance, many products can’t kill clostridium difficile, a gastrointestinal scourge, or the hepatitis A virus, which inflames the liver. Yet by killing other, more common bugs, they can claim 99.9% effectiveness.

Rules governing claims of efficacy vary by agency. In the U.S., the EPA oversees claims about products intended for inanimate objects, while the FDA regulates skin products, including hand sanitizers. To claim that other microbe-unfriendly products such as household cleaners kill 99.99% of germs, companies are permitted to show such deadliness less than 99.99% of the time, according to the EPA’s rules. The standard test is run on 60 slides inoculated with a specific bug, and 59 of them treated with the product must exhibit the claimed rate of germ death. The 60th can fail to allow for a mistake on the part of testers, according to Jean Schoeni, director of research at TRAC Microbiology, which conducts EPA testing. “It’s a very fussy, particular test,” Dr. Schoeni says. Furthermore, if fewer than 59 slides show the high kill rate, manufacturers get a do-over.

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If trained lab testers sometimes need a redo, aren't consumers wielding a spray bottle likely to fall short of optimal sanitizing technique? "It's highly likely," Dr. Schoeni says. She notes that some products need to sit on surfaces for 10 minutes to attain desired kill rates, yet many home cleaners are likely to wipe them off long before that.

Some companies would like to say their products kill the swine-flu virus — a claim that some can reasonably make. However, the FDA bars companies from making claims for over-the-counter products about killing viruses, and has recently issued five warning letters to companies “for false/misleading H1N1 claims,” according to an FDA spokesman. H1N1 is, manufacturers say, rather fragile and easy to kill. But because of the FDA rule, many don’t test the efficacy of their products on the virus, says Doug Anderson, president of ATS Labs, which studies germ-killing products.

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