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How dirty is your toothbrush? Answer: Not as much as you think

You might not need to throw away that toothbrush after a sore throat, a new study shows
You might not need to throw away that toothbrush after a sore throat, a new study

It’s common wisdom as old as your grandmother – after a child has had strep throat, flu or some other similar infection, it’s important to throw away that contaminated old toothbrush and get a new one.

But a new study being presented on Saturday challenges this assumption. A team of experts couldn’t find any strep germs on toothbrushes used by children with strep throat. But they did find potentially nasty germs on two brand-new toothbrushes right out the package.

“I was just dumbfounded,” says Dr. Lauren Shepard of the University of Texas Medical Branch (UTBM) in Galveston, who will present her findings on Saturday at a meeting of the Pediatric Academic Societies.

Tests of toothbrushes from more than 40 children showed just one contaminated with group A Streptococcus – the bacteria that causes strep throat. And that one came from a child who did not have strep throat. Not a single toothbrush from 16 kids with strep throat produced the bacteria.

“They grew the normal stuff but they did not grow strep. That really surprised us,” Shepard said in a telephone interview.

Shepard says she had been curious about the toothbrush issue for a while. She wanted to see if throwing away a toothbrush after an illness might have an effect on children.

“When I was doing my research I realized there were no other studies about throwing away your toothbrush after you have had strep. I thought, ‘how is this possible that no one has ever looked at this?’ I have been told this all my life,” Shepard says.

So Shepard’s team set up a series of studies – first making sure that it is possible to even culture bacteria off toothbrushes – it is – and then trying to simulate a real-life test.

“What we ended up doing was devising a way to collect real kids’ toothbrushes,” Shepard said. They set up shop in an urgent care clinic, offering free toothbrushes to kids who took part in the study.

“We bought these toothbrushes that had a little light in them. Of course the kids liked that,” Shepard said. The light is set to blink for a minute or so, to ensure children brush thoroughly.  “The toothbrushes came two to a pack, so we took one and the kids got to keep one. Everybody did it because they wanted the toothbrush.”

The children brushed for one minute, without toothpaste, and then the toothbrushes were stored in a sterile bag for testing.

They were unable to grow Streptococcus A bacteria off any of the toothbrushes from infected children. A single child who wasn’t sick had Strep A on her toothbrush, Shepard says. It's possible the child was a so-called strep carrier -- someone who carries the bacteria without showing any ill-effects, she said.

"This study supports that it is probably unnecessary to throw away your toothbrush after a diagnosis of strep throat," said Dr. Judith Rowen, a strep specialist and pediatrician at UTMB who worked on the study.

“Maybe the strep is just growing down on the tonsils,” Shepard adds. “It might be it doesn’t actually grow on the teeth as much.”

Strep can live outside the body for days, Shepard says. And, she says, toothbrushes don't really dry out overnight, so it it not unrealistic to think someone could be re-infected by a contaminated toothbrush.

An even bigger surprise – they tested two brand-new, unused toothbrushes as a control. But they found bacteria on them.  

“When we took them straight out of the package using our own sterile techniques … both of them grew something,” Shepard says. One grew staphylococcus – a fairly common bacteria – and another grew some type of bacillus, perhaps E. coli or some other very common germ.

“Even the microbiologists thought that was pretty gross,” Shepard says. “They were like, ‘Oh, I can’t believe they grew stuff’.”

It might be worth rinsing even a brand-new toothbrush, Shepard says. “It’s not like a true health hazard but you should be aware when you take it out it’s not sterile,” she said.

The American Dental Association agrees there's little evidence that any germs on a toothbrush could hurt you. But the organization recommends that people not share toothbrushes or store them in closed containers that might encourage the growth of bacteria. They should be thoroughly rinsed, and replaced every three to four months --mostly because they become frayed and less effective.

"While there is evidence of bacterial growth on toothbrushes, there is no clinical evidence that soaking a toothbrush in an antibacterial mouthrinse or using a commercially available toothbrush sanitizer has any positive or negative effect on oral or systemic health," the group says. "Some toothbrush cleaning methods, including use of a dishwasher or microwave oven, could damage the brush."

As for tossing the toothbrush after an illness? Don’t bother, the researchers advise.