By Kelly A. Reynolds, MSPH, Ph.D.

The source of contamination in drink machines, water dispensers and stored water is often from users’ hands, where fecal bacteria can be contamination in drink machines, water dispensers and stored water is often from users’ hands, where fecal bacteria can be present. In the water cooler study, no frank bacteria or fecal bacteria were found but more recently, 11 percent (10/90) of soda fountains from fast food restaurants around Roanoke, VA tested positive for E. coli, a fecal indicator bacteria.

A recent survey of bacterial contamination in soda fountains brings back memories of previous outbreaks and raises questions of the human health risks associated with microbes in drink dispensers. This review clarifies some common misconceptions on the topic and offers simple solutions to minimize the risks.

Bountiful bacteria
According to a recent scientific report, scuttlebutt may not be the only thing you get at the office water cooler. In 2006, a study in the Journal of Food Protection documented the bacteriological quality of water dispensed from three water coolers over three months.1 The hygiene of dispensed water, chilled and unchilled samples, was evaluated from 174 samples. Source water (20-L bottles of spring water) and dispensed water both tested positive for aerobic plate count (APC) bacteria (i.e., the generally harmless kind found everywhere), with about a 10-fold higher concentration in dispensed water, suggesting that bacteria are growing in the cooler water before being consumed. Data on increased concentrations of general bacteria are often misunderstood. It is not unexpected for bacteria to grow when held stagnant for even short periods of time. For example, bottled water often has higher concentrations of general bacteria than frequently used tap water since bottled water sits on the grocery shelf for longer periods, allowing regrowth of background bacteria. Is this a cause for concern?

Consider that a similar trend occurs with milk. The closer milk gets to the expiration date, the higher the concentration of bacteria, until it eventually spoils. Prior to spoilage, changes in the bacterial population can be smelled and tasted but that doesn’t necessarily mean there is a significant health risk. Monitoring of general plate count bacteria is useful as a measure of what might happen if a harmful bacteria or other pathogenic microbe is introduced into the product. If general bacteria can regrow in the product, harmful bacteria might increase in numbers as well, if introduced.

Pathogens—how did they get there?
This brings us to the need for evaluation of how pathogens might be introduced into a product. First, source ingredients (i.e., water, syrups, powdered flavorings) are always going to have some bacteria present—usually the harmless type. No one expects these products to be sterile. Pathogens, however, are also not expected to be present. Pathogens, instead, are introduced due to a contamination event such as a failed treatment/manufacturing process or posttreatment pollution.

E. coli is found in the gut of humans and other warm-blooded animals. The detection of E. coli indicates that fecal contamination has occurred and that other harmful fecal bacteria could potentially be present. Researchers speculate that hands or wet rags used to wipe down the machines are the source of fecal contamination.

The water treatment industry has addressed this issue, in part, with engineered controls. Some manufacturers have made it more difficult for users to contact the dispense nozzle by covering that part of the machine. Similarly, numerous studies in the developing world have shown that if you can prevent users from putting hands in their drinking water, fecal bacteria counts are dramatically reduced. A simple, engineered control was to provide users with water holding jugs that had an opening smaller  than a young child’s hand.

Controlling unknown sources
In another study, high levels of Bacillus cereus were found in vended hot chocolate following reports of food poisoning among employees at a manufacturing plant.2 Although the source of the toxin-forming bacteria was unknown, B. cereus is commonly found in soil, dairy products and grains. Thus, dried milk products and cocoa were suspected. Under the right conditions of warm water and pooled hot chocolate, in some areas of the machine, the bacteria easily grew to disease-causing levels. Daily cleaning of the hot chocolate vending machine was recommended to prevent growth of B. cereus.

Contamination of vending machines poses a higher risk in sensitive populations. Two separate outbreaks of Legionella and Mycobacterium (common regrowth bacteria in water distribution systems and premise-plumbing) were linked to ice vending machines in hospitals. The outbreaks were halted only after a thorough cleaning and disinfecting of the machines and replacement of the water filters.3,4 Both of these bacteria are primarily nosocomial (transmitted in hospitals) and opportunistic (infecting mostly immunocompromised individuals). Proper maintenance and frequent filter replacement in such environments is especially critical due to the increased risk of infection in susceptible populations.

The food service industry responds
Industry representatives from major manufacturers, the National Restaurant Association and the American Beverage Association point out that stringent standards and guidelines are in place for ensuring the quality of dispensed beverages, and that “[the] industry meets, and often exceeds, all government health standards in bringing its products to market”.5 The problem appears to be in the maintenance of food-service equipment. As with the use of POU water treatment devices, in isolated sites, it is difficult to ensure that proper methods for cleaning and sanitizing equipment, or filter maintenance, are being followed.

Service technicians note they sometimes encounter heavy growth inside the machines and notice poorly handled water bottles nearby that are exposed to heavy foot traffic in and out of office buildings, real estate offices, dental offices and the like. This is a classic case of untrained personnel handling life-support water, not knowing that they could be responsible for causing gastrointestinal problems with staff, or worse.

Documented outbreaks from vended drinks are rare, although such events are difficult to document and are thought to be greatly underreported. One of the largest documented outbreaks from a soda vending machine occurred in an army military compound. Clinical samples determined the cause of the outbreak to be norovirus, a common gastrointestinal pathogen, while the epidemiological investigation revealed evidence consistent with a point-source contamination of food or drink. That point-source contamination was eventually determined to be the soda fountain.6 The outbreak resulted in hospitalization of 99 soldiers, or 12 percent of the army compound. Researchers estimated that another 106 soldiers were sickened but did not require hospitalization and thus did not report their illness. Since human viruses need a host cell to grow and will not multiply in the environment, norovirus contamination of the soda fountain was likely due to an ill server.

Random outbreaks and monitoring surveys that make newspaper headlines remind us, as an industry, not to be complacent about the need to educate vendors and consumers about the importance of proper maintenance of food service equipment. By supplying quality source water, fittings, fixtures, tubing, filters, etc., the water treatment industry plays an important role in the food-service industry. Potential uses, or misuses, of vending equipment should be anticipated and engineered controls implemented whenever possible. Educational outreach efforts designed to increase the quality of the vended product should also continue.

As with most routes of infectious diseases, good personal hygiene and the absence of ill servers will reduce contamination risks. Whether we are talking about the generally harmless bacteria, found everywhere, or frank pathogens, bacterial regrowth in vending machines is expected, but can be minimized by routine cleaning, disinfecting and filter maintenance.


  1. Baumgartner, A., Grand, M. 2006. Bacteriological quality of drinking water from dispensers (coolers) and possible control measures. Journal of Food Protection. 69 (12): 3043-3046.
  2. Nelms, P. K., O. Larson, D. Barnes-Josiah. 1997. Time to B. cereus about hot chocolate. Public Health Reports. May/June 112: 240-244.
  3. Schuetz, A. N., R. L. Hughes, R. M. Howard, T. C. Williams, F. S. Nolte, D. Jackson, B. S. Ribner. 2009. Pseudo-outbreak of Legionella pneumophila serogroup 8 infection associated with a contaminated ice machine in a bronchoscopy suite. Infection Control and Hospital Epidemiology. 30: 461- 466.
  4. Gebo, K. A., A. Srinivasan, T. M. Perl, T. Ross, A. Groth, W. G. Merz. 2002. Pseudo-outbreak of Mycobacterium fortuitum on a human immunodeficiency virus ward: transient respiratory tract colonization from a contaminated ice machine. Clinical Infectious Disease. 35: 32-38.
  5. Park, M. 2010. Soda fountains contained fecal bacteria, study found. International. soda.fountain.bacteria.
  6. Arness, M. K., B. H. Feighner, M. L. Canham, D. N. Taylor, S. S. Monroe, T. J. Cieslak, E. L. Hoedebecke, C. S. Polyak, J. C. Cuthie, R. L. Fankhauser, C. D. Humphrey, T. L. Barker, C. D. Jenkens, D. R. Skillman. 1998. Norwalk-like viral gastroenteritis outbreak in U.S. Army trainees. Emerging Infectious Diseases. 6: 204-207.

About the author
Dr. Kelly A. Reynolds is an Associate Professor at the University of Arizona College of Public Health. She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at





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