[Giardiasis: a parasitic disease of continued topicality. Study of prevalence among a selected adult population].

We studied the prevalence of Giardia intestinalis in five patients risk groups including institutionalised psychiatric of elderly subjects, HIV-positive immunocompromised patients, immigrants from developing countries and travellers to tropical countries. Stool specimens of 1319 subjects were studied. Stools were collected in triplicate from each subject. The presence of bacteria, viruses and parasites was evaluated. A direct smear examination from fresh faecal specimens and after concentration with formalin-ethylacetate was performed for parasite examination. Smears were also stained by a modified acid fast method and then examined for the presence of Cryptosporidium spp. and other coccidia. Cryptosporidium parvum and G. intestinalis were also detected by immunofluorescent assay. Contemporaneously a microbiological investigation was performed with standard culture, biochemical techniques and viral detection. Clinical data about each subject were provided by standardised questionnaires. G. intestinalis was detected in the stools of 41 subjects (3.5%). The immigrants (5.5%), the institutionalised psychiatric patients (5.0%) and HIV immunocompromised patients (4.6%) showed the highest prevalence. By contrast, travellers showed the lowest prevalence (2.5%). G. intestinalis was the pathogen most frequently detected. The cohorts with the presence of more risk factors showed the highest prevalence. The low prevalence of the parasite among travellers demonstrated the significance of health education before travelling and of the most important role of bacterial etiopathogenesis in "traveller's diarrhoea". Epidemiologically, G. intestinalis remains a protozoon of evident importance and is significantly present in Italy.