OCCURRENCE OF CRYPTOSPORIDIUM IN GROUNDWATER WELLS WITH AND WITHOUT SURFACE WATER INFLUENCE

Groundwater is generally considered protected from microbiological contamination by the filtering capacity of overlying soil, so the occurrence of relatively large microorganisms, like the parasitic protozoan Cryptosporidium, is assumed to be low. Surface water is more likely impacted by pathogen sources like wastewater and agricultural wastes. As a result, the influence of surface water is expected to increase a groundwater resource’s susceptibility to contamination, including Cryptosporidium. However, data on the occurrence of Cryptosporidium in groundwater is scarce, and the role of surface water influences on Cryptosporidium presence is often assumed but rarely documented. Our objective was to assess whether the occurrence of Cryptosporidium in groundwater was associated with surface water by analyzing samples from groundwater wells with and without surface water influence. Furthermore, we aimed to compare results from the traditional immunofluorescent assay (IFA) for Cryptosporidium to results from the molecular analysis quantitative polymerase chain reaction (qPCR), as such methods are becoming routine for pathogen detection. We sampled 146 public wells in Minnesota bimonthly for 1 or 2 years totaling 964 samples. Approximately 800 liters of groundwater were sampled using ultrafiltration. Cryptosporidium was quantified using microscopic counts of oocysts and qPCR. Forty percent of wells were positive for Cryptosporidium by qPCR, including both wells with (43%) and without (40%) evidence of surface water influence. Concentrations for qPCR ranged from very low (<1 gene copy per liter) to over 200 gene copies per liter. Correlations between IFA counts and qPCR concentrations are pending. While it is generally assumed that larger organisms like Cryptosporidium are filtered out of groundwater, qPCR results showed that Cryptosporidium may be more common in groundwater than expected. Furthermore, the widespread occurrence of Cryptosporidium in wells that are not under the influence of surface water contradicts conventional thought on groundwater contamination. Results will further our understanding of the occurrence of Cryptosporidium in groundwater and its association with surface water influences on wells.