Oocyst Contamination in Drinking Water: A Case Study in Italy.

The aim of this study was to evaluate the occurrence of oocysts in a drinking water treatment plant (DWTP) located in a rural area of northern Italy. Influent and effluent samples were collected at the DWTP over three years (2013-2016). In parallel, tap water samples from a public drinking fountain were collected as well. All samples were analyzed for the presence of spp. oocysts by a common method based on an immunomagnetic separation (IMS)/immunofluorescence assay (IFA), complemented by 4,6-diamidino-2-phenylindole (DAPI) staining. A reverse transcriptase-PCR (RT-PCR) protocol was added to evaluate oocyst viability. The results highlighted a high variability of oocyst concentrations across all samples (mean 4.3 ± 5.8/100 L) and a high variability in the percentage of DAPI-positive specimens (mean 48.2% ± 40.3%). Conversely, RT-PCR did not reveal the presence of viable and oocysts. A nested PCR targeting 18S ribosomal DNA, carried out in two water samples, confirmed the presence of a genotype associated with wild animals in the river and in tap water. The results obtained underline the vulnerability of the investigated surface water to spp. contamination. Although the recovered genotype is not a human pathogen, its presence demonstrates the existence of a potential pathogen spp. contamination risk. Moreover, these results underline the importance of also considering unconventional (not bacterial) biological contaminations (protozoa) in water resources in rural areas, including those of developed countries.