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Double-dipping: Beware what your party spread might be spreading

We ask the experts to settle common questions we've all wondered about.

QUESTION: How big a health problem is double-dipping at social gatherings? If you take a bite of a chip and then put it in the dip a second time, can you really spread potentially harmful germs to others? And, if so, what type of germs?

ANSWER: Many party-goers indulge in the guilty pleasure of double-dipping.

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While double-dipping is not a huge public-health concern, it definitely means you are sharing your germs with others, and therefore is not risk free. I wouldn't double-dip - even with my closest friends.

We all carry thousands of different bacteria and viruses on our skin, and inside our mouth. The great majority of these do not cause harm; but some of them may.

With double-dipping, you may transfer the bacteria or viruses present in your mouth to the dip. The risk to someone else who dips after you depends on which bacteria or viruses you have in your mouth at the time, how many of them get into the dip, and how well they survive in the dip. In dips with thick consistency, like chocolate, bacteria tend to stay on a chip, rather than being transferred to the dip. Bacteria and viruses are less likely to survive dips that are hot (like nacho cheese), or are acidic (like salsa) than other types of dips.

Overall, a study by Paul Dawson, a professor of food science at Clemson University in South Carolina, found that there were 1,000 times more bacteria in dip that had been double-dipped than dip that was fresh. Note, however, that the person who is making the dip can also contaminate the dip with bacteria from their mouth or fingers - double-dipping may make things worse, but it isn't the only source of bacteria or viruses in dip.

To help clarify the potential risk: There are two main categories of infections you can spread by dipping your chip, cracker or carrot stick after it's been in your mouth - viral infections and bacterial infections.

Examples of viral infections that can be spread through saliva are influenza, mumps and cytomegalovirus (CMV). Influenza technically lives in the respiratory system, but it can get into one's saliva or mouth by sneezing, which makes it possible to transmit influenza by double-dipping. Mumps is spread through saliva and other bodily fluids, making it another risk for double-dipping. The infection, which causes painful swelling of the salivary glands, is prevented by a vaccine. If you do contract mumps, only the symptoms - not the infection - can be treated.

Lastly, CMV is a herpes virus that causes rashes, affects other organs and can be life-threatening for patients who are immuno-compromised, such as those with HIV or someone who recently received an organ or bone-marrow transplant.

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The other concern is bacterial infections. A serious infection that can be passed by saliva is meningococcal meningitis. This potentially life-threatening infection is spread through saliva and causes inflammation to the protective membranes covering the brain and spinal cord.

Instead of calculating the risk every time a dip is served, practice safe dipping by dunking each chip, cracker or carrot stick once only or by spooning the dip onto your individual plate.

Dr. Oscar Larios is an Infection Control Fellow at Mount Sinai Hospital in Toronto.

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