In recent years, the availability of ready-to-eat vegetables, especially prewashed salad greens and other vegetables that do not require cooking, has increased the risk of Cryptosporidium infection.
According to a recent study published in Parasitology Research, 58% of samples taken from ready-to-eat salads (cut and pre-washed) and pre-washed vegetables sold in UK supermarkets tested positive for the Cryptosporidium parasite.
What is Cryptosporidium?
According to EODY, Cryptosporidium is an intracellular parasite of the order Apicomplexa that infects humans, cattle, birds, fish and reptiles. It completes its life cycle within the host by forming cysts that are excreted in the feces, thereby infecting new hosts. Although 22 species of Cryptosporidium have been described, almost 90% of cases of cryptosporidiosis in humans are attributed to only two species, C. hominis (formerly known as C. parvum genotype 1) and C. parvum. The cryptosporidia C. meleagridis, C. canis, C. felis, C. suis, C. muris, C. fayeri, C. ubiquitum, and C. cuniculus rarely cause disease in humans.
The parasite is protected by an outer shell, which allows it to survive outside the host for long periods of time and makes it highly resistant to chlorine levels commonly found in drinking water and swimming pools. Boiling is the most common method of removing the parasite from water. In contrast, antiseptic hand gels have no effect on the microorganism.
Cryptosporidium is distributed worldwide and can be found in surface water, swimming pools, day care centers, and hospitals.
Symptoms of cryptosporidiosis
The clinical picture of the disease mainly consists of severe watery diarrhea, abdominal pain and abdominal cramps, loss of appetite, fever, nausea, vomiting and dehydration.
In people with a normal immune system, the infection is either asymptomatic or presents with acute episodes of diarrhea, while a small proportion of people experience persistent diarrhea lasting several weeks.
What research has shown about ready-to-eat salads
As part of the study, the researchers evaluated samples of pre-washed vegetables taken from various supermarkets in Kent, England, to check if they were contaminated with the parasite.
A 2015 study reported the largest outbreak of cryptosporidiosis to date in Scotland and England, with 74 confirmed cases, linked to contaminated pre-cut vegetables sold in supermarkets.
Also, a recent outbreak of the same disease, with more than 2,400 confirmed cases in 2023, has been linked to exposure to the pathogen through livestock, swimming pools, foreign travel, and food.
However, in recent years, the availability of ready-to-eat vegetables, especially prewashed lettuce and other vegetables that do not require cooking, has increased the risk of Cryptosporidium infection.
For this latest study, researchers collected 36 samples of prewashed vegetables from four supermarkets in Canterbury. The results showed that 58% of the samples were positive for Cryptosporidium and four out of 24 samples were positive for C. parvum.
Vegetable samples that were pre-washed and cut and tested positive for cryptosporidium were mainly red cabbage, iceberg lettuce, carrots, spinach, Swiss chard, and red and green lettuce.
Because pre-cut and washed vegetables are meant to be eaten as a salad without cooking, they are washed with more chlorine than unpackaged and uncut vegetables.
However, the resistance of cryptosporidium to chlorine-based disinfectants results in its persistence in vegetables and causing parasitic infections.
Contamination of vegetables can occur at any stage of production, water used for irrigation, processing, packaging or transportation. Additionally, these vegetables may come into contact with other unprocessed vegetables during packaging or transportation, leading to cross-contamination.