The Scenario: Ah, your friend's trusty old kitchen sponge. That old, old, old kitchen sponge. When you arrive at her place with Thai take out, she gets dishes from her drying rack. You cringe. That sponge leaning on the edge of the sink looks filthy.
All that's left to scour those plates is a shredded brown tuft where the scrubbing side used to be. You're wondering what's living on the underside of that sponge, and whether it'll sprout little spongy legs, become sentient, and wash the dishes for her. What happens if your friend never changes her kitchen sponge?
The Reality: That sponge is a haven for bacteria and is likely dirtier than her toilet. "If bacteria were going to heaven, it would be called a sponge," says Charles Gerba, a professor of microbiology and environmental sciences at The University of Arizona's Mel & Enid Zuckerman College of Public Health. "It's got everything they want—particularly salmonella, which can cause foodborne disease."
Gerba has conducted studies on bacteria in sponges for years. Back in 2000, he tested over 100 household sponges across America and found that 15 percent of them had salmonella, fecal matter, and other bacteria. And it's still a problem: His recent study found household kitchen sponges harbored bacteria that could play a huge role in cross contamination, including potential pathogens, during food prep. Experts actually recommend tossing your kitchen sponge once a week—even more frequently if someone in the house is sick.
The Worst That Can Happen: A nasty old sponge could lead to the spread of foodborne, potentially pathogenic diseases, according to a recent study published in Scientific Reports. The study found that kitchen sponges "collect, incubate and spread bacteria" which can get into the human body via hands and/or contaminated food. If your friend touches the offending sponge with their hands, they may transfer the bacteria into and on their bodies, possibly causing pathogenic infections like salmonella, leading to symptoms such as diarrhea, chills, dehydration, fatigue, and fever. She could recover in a week or even require medical care such as IV fluids and antibiotics. In the worst case—and exceedingly unlikely—scenario, your friend could die; the CDC reports that 380 deaths in the United States are due to salmonella poisoning every year.
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What Will Probably Happen: Cutting apples on the same wooden board you tenderized a raw steak on beforehand makes your friend's sponge a cross contamination assassin in your home. "You're picking up salmonella after cleaning up a raw meat product and then it grows, and then you wipe down some other area where you might put a salad and then you get it on your hands," Gerba says. "You contaminate food when you're making other food." In other words, your raw meat could be getting into kale salad since it was on the same cutting board, which could could you sick, meaning hours of quality toilet time.
What to Tell Your Friend: Tell your friend to replace her new sponge with a new one every week or two. "The bacteria, in about four or five days, starts to hit the billions inside the sponge," says Gerba. Yes, your friend could nuke the old one in the microwave for 30 seconds, which Gerba says works well, but the Scientific Reports study shows bacteria can cling to your friend's sponge even during the disinfecting process.
In fact, the Scientific Reports study showed "regularly sanitized sponges," including ones that were boiled, didn't have less bacteria than uncleaned ones, and even had increased bacteria counts of both the Moraxella– and Chryseobacterium–affiliated bacteria as measured in operational taxonomic units, or OTUs (a measure of microbial diversity in datasets). Bottom line: Sanitizing that dirty sponge over and over again won't cut it—and it could even make it worse.
If your friend wants to get out of the sponge business altogether, Gerba recommends using paper towels to clean the kitchen. "Some people don't think that's environmentally friendly, but if you get diarrhea, you're going to be using a lot more toilet paper than paper towels."
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