Those soda fountain machines found in restaurants and fast food joints may be squirting out liquids contaminated with fecal bacteria, a small study found.
Whether it was self-serve or behind the counter, nearly half of all sodas dispensed from a sample of 30 machines in the Roanoke Valley in Virginia had coliform bacteria -- a group of bacteria banned in drinking water by the U.S. Environmental Protection Agency (EPA) because it indicates the possibility of fecal contamination.
"The EPA regulates our drinking supply, and there can be some bacteria, but one of the things that is not allowed is coliform bacteria," said Renee D. Godard, professor of biology at Hollins University and a co-author of the paper published in the January print issue of the International Journal of Food Microbiology.
"We can't have that in our drinking supply. But they're coming out of these soda fountain machines," she said.
The soda machines had turned into a bacteria metropolis with Escherichia coli (E. coli), species of Klebsiella, Staphylococcus, Stenotrophomonas, Candida, and Serratia. Most of the bacteria were resistant to the 11 antibiotics Godard tested on her samples.
"About 70 percent of the beverages had bacteria and 48 percent of them had coliform bacteria," said Godard.
However, only 20 percent of the sodas sampled had coliform bacteria that exceeded the EPA limit for drinking water.
Since the tap water and ice from the machines didn't test positive for bacteria, Godard and her team ruled out the possibility of a valley-wide contamination of the water supply.
Various brands of soft drinks and various types -- sugared, diet or even water -- were contaminated, leading Godard to think that it wasn't the soda, but the machine that was growing bacteria.
From all her testing, Godard still isn't sure where the bacteria came from. Few people observed in the restaurants touched the nozzles of the soda fountain machines and restaurant managers Godard interviewed reported cleaning the nozzles daily.
But only one restaurant manager reported rinsing the plastic tubing within the machines on a regular basis.
How Could Soda Fountain Machines Grow Bacteria?
Godard hypothesizes that it could only take one contamination of the nozzle for the bacteria to grow up into the plastic tubing and start colonizing within the machine.
"Our best guess is they're actually establishing themselves on the lining of the plastic tubing. The reason we say that is in other areas, such as hospitals, it is known that bacteria can establish themselves on plastic tubing for machines," said Godard.
The Coca-Cola Company, said in a statement to ABCNews.com that it "has been serving fountain beverages for more than 120 years, and we are not aware of any illnesses related to our fountain-dispensed beverages and the microorganisms mentioned in the Virginia study."
Coca-Cola said it purchases the soda fountain dispensers from independent companies and "routinely communicate with our customers, who maintain the fountain equipment, about our standards and expectations for quality and sanitation, and we provide them with training," according to the company's statements.
Godard said she hopes the news will lead restaurant owners to rinse out their machines more often.
However, Godard pointed out that the most common model of soda fountains in her study -- manufactured by Cornelius Inc. -- recommended flushing out the internal tubes at least once a month and daily cleaning of nozzles.
"But my guess is that most restaurant owners wouldn't have the vaguest idea about how to flush those machines, or that they would even need too," said Godard.
Microbiologists not involved in the study weren't surprised of coliform colonies in the soda fountain machines.
"Wherever man is there will be representation of feces," said Philip Tierno, director of Clinical Microbiology and Immunology at New York University Langone Medical Center.
"We're basically bathed in feces as a society," he said.
How To Prevent Bacteria in Soda Fountain Machines
Charles Gerba, a microbiologist at the University of Arizona was "not too surprised" to learn coliform bacteria were found in soda fountain machines either.
"We've seen it with drinking water dispensing machines where customers fill up jugs of water," said Gerba. "You see it anytime you have something where people can touch the dispenser."
As gross as the contamination sounds, experts weren't too worried about becoming infected from the bacteria found in the study unless a person is immunocompromised through cancer treatment, medications following an organ transplant or if they have AIDS.
After all, there haven't been any outbreaks of gastrointestinal disease reported in Roanoke Valley or across the nation recently.
But microbiologists did see the soda machines as potential hosts for more threatening bacteria and viruses.
Who Should Care About It?
Godard thought it was possible that a more virulent strain of E. coli could grow in the machines since her group found a less dangerous form.
"There are strains of E. coli that aren't dangerous," she explained.
Gerba and Tierno were also concerned about the possibility of a serious Norovirus outbreak. They reason if fecal contamination can spread to soda fountain dispensers, then viruses spread by fecal contamination could, too.
"That's what I would worry about because you get one of these tips contaminated and you contaminate a lot of soda," said Gerba. "It suggests it's a route for transmitting something like Norovirus because fecal contamination is occurring."
One such incident occurred in 2000 on a military base hospitalizing 99 soldiers with gastrointestinal illness, according to Godard's paper.
Tierno thought restaurants could avoid potential Norovirus outbreaks by taking measures similar to cruise ships, which have implemented strict rules in cafeterias since a string of Norovirus outbreaks in the last decade.
"Bottom line -- there should be better cleaning of the instruments, and probably the public should not have access to dispensing their own sodas," said Tierno.