# Food and Drinking Water as Sources of Pathogenic Protozoans: An Update
## 5 Giardia intestinalis
### G. intestinalis Infections from Food and Drinking Water  
Foodborne transmission of giardiasis achieved increased relevance in recent years, and in the USA, 7-15% of _G. intestinalis_ infections were probably foodborne [26], with 38 outbreaks reported from 1971 to 2011. Foods involved were fresh produce, fresh fruits, caused salmon, raw oysters, ice cream, noodle salad, chicken salad, dairy products, sandwic, and tripe soup [147]. In the USA, some outbreaks until 2018 were also caused by unpasteurized milk, shellfish, and non-identified foods served in restaurants or communities such as offices, schools, and camps. In twelve cases, infected food handlers were the cause of food contamination and _G. intestinalis_ was frequently identified in fecal samples and under their nails. Sub-assemblages All and BIV were detected both in food handlers and in students in public schools in Angulo, Brazil, and sub-assemblage BIII transmitted by infected food handlers in a grocery store chain caused an outbreak in New York, USA [26]. A study in an urban area of southern Brazil identified the same assemblage B genotype, with 100% _gdh_ gene sequence similarity in humans, one dog, and two lettuce samples, suggesting a linkage with irrigation water possibly contaminated from septic tanks. In another study, whole-genome sequencing (WGS) showed that _G. intestinalis_ from bewers was the cause of two waterborne outbreaks in a small community [26]. Waterborne outbreaks of giardiasis in Europe were mainly reported in Nordic countries, including a large outbreak in Bergen, Norway, which involved around 6000 cases in 2004 [154]. In Africa, the pooled prevalence estimate of _G. intestinalis_ contamination from waterbodies detected by microscopy was 11.9% from a total of 7950 samples, with the highest rate of 37.3% in Tunisia [155]. In January 2019, a giardiasis outbreak caused by tap water, according to patients' interviews, involved more than 200 individuals in Bologna, Italy. _G. intestinalis_ cysts were not detected in water samples from the distribution network during the outbreak and the additional monitoring period, so it was hypothesized that water contamination occurred during working operations carried out on the water supply network before the outbreak and was no longer detectable [154]. _G. intestinalis_ cysts have been detected on fresh produce, including leafy greens, herbs, berries, fruits, green onions, carrots and tomatoes, dairy products, meat, shellfish, and processed foods [26; 147]. For ready-to-eat vegetables and salads in supermarkets, the contamination percentage ranged between 0.5% in Palermo, Italy and 1.8% in Canada. On unwashed vegetables, the highest contamination percentage was 55% in Ilam City, Iran, followed by field-collected vegetables in Valencia, Spain (52.6%). _G. intestinalis_ assemblages A, B, C, and D were reported in the hemolymph of shellfish [26]. Generally, the numbers of cysts recovered from fruits and vegetables were low but real contamination rates were probably higher due to the poor recovery of _G. intestinalis_ cysts from food. Washing fruits and vegetables can reduce the risk of contamination. However, in a study in Nepal, it was reported that even when treated water was used for washing vegetables, the contamination levels were higher than the infectious dose of 10 cysts [26]. Contamination of fresh produce may originate either from contaminated fertilizers, livestock, and other animals with access to the fields or directly from the hands of infected workers or equipment [147]. In Cote d'Ivoire, quantitative microbial risk assessment (QMRA), which estimates the risk of infection from exposure to a microorganism, assessed an annual risk of infection with _G. intestinalis_ of 0.36 and a probability of becoming ill from eating vegetables grown locally of 1.0%. In many countries, the risk of giardiasis from eating vegetables irrigated with wastewater was higher than acceptable, with a maximum of 100% in Thailand.