Cryptosporidium and Giardia

In The November 2001 issue of the Journal of Food Protection, a group of Norwegian researchers reported finding parasites on fruits and vegetables in Norway.  Of 475 samples of various fruits and vegetables collected from produce distributors, 19 tested positive for Cryptosporidium and 10 tested positive for Giardia.  Of the positive Cryptosporidium samples, 14 (74%) were from mung bean sprouts.

One sample of radish sprouts was found to be positive for Giardia.  This one sample represented 10% of the fruit and vegetables found to be positive.  This was the first report of these parasites being detected in fruits and vegetables in a highly developed, wealthy country, without being an outbreak situation.    It was also the first study to suggest that sprouts may pose a risk of infection with these parasites.

Although there was a higher incidence of these parasites in sprouts than in other produce, the researchers did not consider them to be any greater health risk than other produce.  They concluded that because these parasites do not amplify outside their hosts, the “adverse public health consequences are similar for sprouts to those of other products, or, indeed, less due to the extensive washing during sprout production“.  With respect to all produce, the paper concluded that, “These findings may have important implications for global food safety.”

The researchers further investigated sprouts and reported their findings in 2002 in the International Journal of Food Microbiology.  After spiking sprouts and sprouting seed with known amounts of Cryptosporidium and Giardia, they were able to determine that the pathogens could survive in sprouts, though the populations were reduced.

They also tested mung bean seed they picked up from a local sprout producer and found six (75%) of the eight samples harbored one or both parasites.  All six of the contaminated samples were positive for Cryptosporidium and three of those samples also contained Giardia.

So what does this mean for the sprouting industry?

Unlike testing for bacteria, in which non-viable cells do not show up in test results, Cryptosporidium and Giardia are housed in an oocyst, which might be likened to a pea pod.   It should be noted that although it is now known that seed and sprouts have the capability to transport Cryptosporidium and Giardia, it is not yet know what percent, if any, of the oocyst protected sporozoites are viable.  It was not within the scope of these studies to assess the viability or infectability of the parasites.

It is likely that many growers have unknowingly handled this problem through proper seed sanitation.  Research suggests that the amount of chlorine needed to neutralize Cryptosporidium oocysts,the CT value (ppm Concentration x Time in minutes) of chlorine needs to be around 8,000 CT for an effective kill.  Giardia is killed at yet far lower concentrations.  The likelihood is that sprout growers, using the US FDA recommended seed sanitizing method (soaking in 20,000 ppm calcium hypochlorite for 10 minutes; CT value = 200,000 CT), are neutralizing the parasites in the process.  Chlorine use in Norway is not allowed on sprouts.

It is also interesting to note that bean sprouts were found to be far more contaminated than the green sprouts.  The research did not indicate what type of growing methods were employed to produce the sampled sprouts.  Whereas bean sprouts are typically watered every 4 hours, green sprouts, grown in trays, are typically watered every 1-2 hours.  Rotary drum grown sprouts can be watered as often as every two minutes, further increasing the probability of rinsing off the parasites.

Both of these parasites are a transmitted to the sprouts via fecal contaminants that hitch a ride on the seed.  If further studies indicate that parasites in the sprouts are viable, even after chlorination, necessitating testing for Cryptosporidium and Giardia, the researchers in these studies propose that the most effective method of detection is to test the seed rather than the sprouts.

We at ISS concur with this conclusion and see no need to sprout seed that contains fecal matter.  ISS Screened Sprouting Seed is tested forgeneric E.coli, among other things.  We continue to believe that although sprouts present special issues because of bacterial amplification, the highly controlled environment they should be produced in, and the ability to test the seed beforehand, gives them the capability of being the safest produce on the shelf.


Cryptosporidium, a protozoan parasite, has been recognized to be a human pathogen since 1976. The protozoate is transmitted by the ingestion of oocysts that have been excreted in the feces of infected humans or animals. Similar to Giardia, Cryptosporidium can also be transmitted by the ingestion of fecal contaminated water. Several species of Cryptosporidium are known to exist but only Cryptosporidium parvum is known to be infective to humans.

After release into the environment, the organism is protected by an outer shell called an oocyst. Each oocyst contains four sporozoites with one nucleus per sporozoite. Upon ingestion, the organism emerges from the shell and infects the lining of the intestine.

The infectious dose is less than 10 organisms and, presumably, one organism can initiate an infection. The mechanism of disease is not known;  however, the intracellular stages of the parasite can cause severe tissue alteration.

Cryptosporidium sp. could occur, theoretically, on any food touched by a contaminated food handler. Though there have been no known outbreaks of cryptosporidiosis associated with the consumption of sprouts, mung bean sprouts have been found to be carriers, with the point of origin being fecal contaminated seed.

Fertilizing salad vegetables with manure is another possible source of human infection. Large outbreaks are associated with contaminated water supplies.

Intestinal cryptosporidiosis is self-limiting in most healthy individuals, with watery diarrhea lasting 2-4 days. In some outbreaks diarrhea has lasted 1 to 4 weeks. To date, there is no known effective drug for the treatment of cryptosporidiosis. Immunodeficient individuals, especiallyAIDS patients, may have the disease for life, with the severe watery diarrhea contributing to death. Invasion of the pulmonary system may also be fatal.


Giardia lamblia (intestinalis) is also a single celled animal, i.e., a protozoa, that moves with the aid of five flagella.  In Europe, it is sometimes referred to as Lamblia intestinalis.

Giardiasis is the most frequent cause of non-bacterial diarrhea in North America.  It may involve diarrhea within 1 week of ingestion of the cyst, which is the environmental survival form and infective stage of the organism.

Normally illness lasts for 1 to 2 weeks, but there are cases of chronic infections lasting months to years. Chronic cases, both those with defined immune deficiencies and those without, are difficult to treat.

Ingestion of one or more cysts may cause disease, as contrasted to most bacterial illnesses where hundreds to thousands of organisms must be consumed to produce illness.

Giardiasis is more prevalent in children than in adults, possibly because many individuals seem to have a lasting immunity after infection. This organism is implicated in 25% of the cases of gastrointestinal disease and may be present asymptomatically.

About 40% of those who are diagnosed with giardiasis demonstrate disaccharide intolerance during detectable infection and up to 6 months after the infection can no longer be detected. Lactose (i.e., milk sugar) intolerance is most frequently observed. Some individuals (less than 4%) remain symptomatic more than 2 weeks; chronic infections lead to a malabsorption syndrome and severe weight loss. Chronic cases of giardiasis in immunodeficient and normal individuals are frequently refractile to drug treatment. Flagyl is normally quite effective in terminating infections. In some immune deficient individuals, giardiasis may contribute to a shortening of the life span.

Giardiasis is most frequently associated with the consumption of contaminated water. Five outbreaks have been traced to food contamination by infected or infested food handlers, and the possibility of infections from contaminated vegetables that are eaten raw cannot be excluded. Though there have been no known outbreaks of cryptosporidiosis associated with the consumption of sprouts, mung bean seed and sprouts as well as radish sprouts have been found to be carriers, with the point of origin on the sprouts likely being fecal contaminated seed.

The United States Environmental Protection Agency Method 1623 (used for detection of Giardia and Cryptosporidium) defines a sporozoite and nucleus in the following manner:

  • Sporozoite – a motile, infective stage of certain protozoans; e.g., Cryptosporidium. There are four sporozoites in each Cryptosporidium oocysts, and they are generally banana-shaped.
  • Nucleus – A membrane-bound organelle containing genetic material. Nuclei are a prominent internal structure seen both in Cryptosporidium oocysts and Giardia cysts. In Cryptosporidium oocysts, there is one nucleus per sporozoite. One to four nuclei can be seen in Giardia cysts.

Cryptosporidium oocysts are 3-7µm in diameter. Serological surveys indicate that 80% of the population has had cryptosporidiosis.