Sprouts are the germinating form of seeds and beans. Sprouts, including mung beans and alfalfa sprouts, have become a common food item in grocery stores, salad bars and Asian dishes. As the popularity of sprouts increases, however, so does the potential for sprout-related illnesses. Most sprouts, including alfalfa sprouts, can only be eaten raw. This means they are not exposed to temperatures high enough to kill bacteria that may be present.

During the past decade, over 20 percent of all produce related foodborne illnesses were associated with the consumption of raw or lightly cooked sprouts. Worldwide, at least 37 outbreaks of foodborne illnesses have been linked to sprouts between 1973 and 2005. In most instances, the illnesses were caused by either Escherichia coli (E. coli) O157:H7 or Salmonella bacteria. The largest outbreak linked to sprouts took place in Japan in 1996, when 6,000 people got sick and 17 died after eating radish sprouts contaminated with E. coli O157:H7.

Scientists believe that the most likely source of contamination is the seeds that are used to grow the sprouts. Seeds may become contaminated by animal manure in the field or during storage, and the conditions required to grow sprouts (e.g, warmth and humidity) are ideal for the rapid growth of bacteria. Poor hygienic practices in the production of sprouts have also caused some sprout-related outbreaks of foodborne illness in the past. Also, sprouts are very democratic, and like all sorts of different pathogenic organisms. Many different serotypes of Salmonella have been implicated in sprout outbreaks, as well as E. coli.

CDC first brought sprouts to national attention as a vehicle for foodborne illness back in 1995. In a 1998 white paper on fresh produce, the National Advisory Committee on Microbiological Criteria for Foods identified raw sprouts as a special food safety problem. In 1999, the National Advisory Committee on Microbiological Criteria for Foods issued a report entitled "Microbiological Safety Evaluations and Recommendations on Sprouted Seeds." Since then, FDA has issued several consumer advisory warnings about health risks associated with the consumption of raw sprouts. FDA also released two guidance documents, one on seed disinfection and the other on testing irrigation water, concerning practices to minimize microbial contamination of sprouts.

Outbreaks implicating sprouts continue to occur, however. Unfortunately, it is difficult to detect pathogens. The contamination is usually non-homogenous, so that sampling sample one part of the seed or the sprout may not provide a representative sample of levels of contamination elsewhere. Also, there can be low levels of contamination which are difficult to pick up on culture methods. Finally, sprouts are rarely cooked or washed by the consumer. Sprouts have also been referred to as a stealth vehicle in foodborne outbreaks, because many people don’t realize they’re eating sprouts. Sprouts are often in salads or in sandwiches and people don’t remember that they ate sprouts. In fact, in many of the outbreak investigations only 30-40 percent of people will outwardly recall eating sprouts.

Anyone who eats raw sprouts or lightly cooked mung bean sprouts, is at risk for exposure to E. coli O157:H7 or Salmonella bacteria. However, the risk of serious health effects is greater for young children, seniors and people with weak immune systems. Persons who belong to those groups at high risk for serious health effects from foodborne illness should avoid eating raw sprouts, especially alfalfa sprouts and mung bean sprouts.