Abstract
Giardiasis, the disease caused by the flagellate Giardia duodenalis (syn. G.lamblia, G. intestinalis), is the most commonly reported among the five food- and waterborne parasitic diseases under mandatory surveillance in 24 EU countries. From November 2018 to April 2019, an outbreak of giardiasis occurred in a municipality of the Bologna province, in north-eastern Italy. Microscopy and immunochromatography identified cysts and antigens, respectively, of the parasite in stool samples of 228 individuals. Molecular typing of 136 stool samples revealed a vast predominance (95%) of G. duodenalis assemblage B. Investigations into potential sources indicated tap water as the most likely vehicle of infection, although cysts were not detected in water samples. Control measures mostly aimed at preventing secondary transmission by informing citizens about the outbreak, and by treatment of patients with anti-parasitic drugs. This is the first documented human outbreak of giardiasis in Italy; its investigation has highlighted the difficulties in the timely detection and management of this parasite, which is often overlooked as a cause of human gastroenteritis. The long and variable incubation time, absence of specific symptoms and a general lack of awareness about this pathogen contributed to delay in diagnosis.
Highlights
The unicellular flagellated parasite Giardia duodenalis infects the gastrointestinal tract of a wide range of mammals [1]
General practitioners (GPs) and paediatricians were informed about the outbreak and encouraged to submit samples from patients presenting with intestinal symptoms
Two additional cases were reported by GPs within week 1 in 2019 in individuals living in the same municipality
Summary
The unicellular flagellated parasite Giardia duodenalis (synonyms, Giardia lamblia, Giardia intestinalis) infects the gastrointestinal tract of a wide range of mammals [1]. Giardiasis is caused by assemblages A and B, two genetically different groups that have zoonotic potential [2]. The simple life cycle comprises the trophozoite, which causes the www.eurosurveillance.org symptoms, and the cyst, the infective stage, which is shed with the host’s stools. Transmission occurs by the faecal-oral route or by ingestion of cysts in contaminated water or food [1]. Water plays an important role in the transmission of Giardia infection; the cysts survive best in cool, damp environments and can withstand chlorination, maintaining their infectivity for weeks. Waterborne outbreaks of giardiasis, have occurred worldwide [3]. In Europe, these have been mainly reported by Nordic countries, including a large outbreak in Bergen, Norway, which occurred in 2004 and involved around 6,000 individuals [4]
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