Nonprofit, nonpartisan journalism. Supported by readers.

UCare generously supports MinnPost’s Second Opinion coverage; learn why.

The pathogen perils of adding ice and lemon slices to your drinks

Another thing: Don’t count on the acid or alcohol in a drink to take care of the contamination.

A 2007 study found almost 70 percent of lemon slices used in 21 restaurants carried bacteria or fungi, many of which were associated with human contamination.

Are you planning to tailgate before the Vikings game on Sunday?

If so, you may want to be careful about the garnishes that go into your drink — specifically, any ice or lemon slices.

Those items just might make you sick. For, as a study published earlier this year found out, the human handling of ice and lemons can easily cause them to become contaminated with bacteria and other pathogens.

Ice has long been known to cause foodborne illnesses. In 1987, for example, contaminated ice served at a football game in Philadelphia led to a four-state outbreak of norovirus in the United States, which left more than 5,000 people ill. And a 1991 cholera epidemic in Latin America, which led to almost 8,000 illnesses and 17 deaths, was traced back to contaminated ice.

Article continues after advertisement

Lemons, too, have been previously identified as potential sources of foodborne illnesses. A 2007 study found almost 70 percent of lemon slices used in 21 restaurants carried bacteria or fungi, many of which were associated with human contamination.

What this new study demonstrates, however, is just how easily pathogens on human hands can get onto ice and lemon slices — and, therefore, into our drinks.

Foodborne illnesses are a major public health problem in the United States. The Centers for Disease Control and Prevention (CDC) estimates that 48 million people get sick from such illnesses every year. Of those, 128,000 people are hospitalized — and 3,000 die.

Most people don’t realize that their symptoms — nausea, vomiting, stomach cramps, and diarrhea — are related to something they ate or drink. Instead, they mistakenly attribute the illness to “stomach flu” or some airborne “bug” they’ve picked up. 

They are certainly unlikely to trace their symptoms back to the ice or lemons in their drinks.

Study details

For the new study, a team of food scientists at Clemson University inoculated the hands of human volunteers with a tiny amount of E. coli bacteria, a common source of foodborne illness. The bacteria had been engineered to contain a fluorescent gene so that its transfer from the volunteers’ hands to other objects could be easily observed.

The hands of a second group of volunteers — the “control” group — were kept E. coli-free.

In a series of experiments, both sets of volunteers were asked to handle (for 30 seconds) ice, dry lemons, wet lemons (ones wetted with water) and utensils (scoops) used to pick up lemons and ice.

Why those particular drink garnishes? 

Article continues after advertisement

“Ice and lemons are often added to beverages — and ice is almost universal in coolers used at tailgates cookouts and other outdoor events,” explain study co-authors, Clemson University food scientist Paul Dawson and doctoral student Wesam Al-Jeddawi, in an article they wrote about their research for The Conversation.

Key findings

The study’s results weren’t pretty.

“The bad news was that when hands were contaminated with E. coli, the bacteria were transferred to wet lemons and ice 100 percent of the time,” Dawson and Al-Jeddawl report. “If the lemons were dry, the bacteria were transferred 30 percent of the time.”

Ice was a particularly effective conveyor of bacteria.

“More bacteria were transferred to ice from hands or scoops than was transferred to lemons — up to 67 percent from hands and 83 percent from scoops!” the researchers note.

And what if you add your own garnishes at a “drink station” rather than letting someone else do it for you? That’s safer, right?

No. Those lemons can become contaminated with bacteria when they are sliced — or when people reach into the bowl to pick one out.

“Making matters worse,” write Dawson and Al-Jeddawl, “the lemons are sometimes open to the air and may or may not be kept cold. In our study we found that when lemons were inoculated with E. coli they increased in population over five times when held at room temperature from four to 24 hours. So a day of people reaching into the bowl for lemon slices might result in a microorganism party.” 

Once last thing: Don’t count on the acid or alcohol in a drink to take care of the contamination. Another study found that pathogens frozen in ice and then allowed to melt survived even in 80- to 86-proof mixtures of Scotch and soda or tequila.

Article continues after advertisement

Consider the source

So, just how concerned should you be about drink garnishes?

“As with most food safety issues, common sense and good sanitary practices win the day,” Dawson and Al-Jeddawl write. “The chance of getting sick from your drink is slim, but it does happen. Since food service workers are the primary source for contamination from norovirus, hepatitis A and certain other bacterial pathogens, it is good to be aware of restaurant sanitation ratings as well as how your food is handled.”

“Thus, watch who is putting what into your drink,” they add. “There might be something riding on that lemon that you don’t want.” 

That includes your friends at this week’s tailgating parties.

FMI: You’ll find an abstract of the study in the Journal of Food Research, but the full study is behind a paywall. You can read Dawson and Al-Jeddawl’s article on their research at The Conversation’s website.