Joanna Ciol Harrison

Project title: Risks associated with exposure to cryptosporidium and giardia parasites in North Seattle recreational waters

Degree: MS | Program: Environmental Health (EH) | Project type: Thesis/Dissertation
Completed in: 2018 | Faculty advisor: John Meschke


Cryptosporidium and giardia are diarrhea-causing microscopic parasites transmitted through ingestion of fecally contaminated water. Both parasites can have a significant impact on the health and financial burden of communities. In King County, WA, annual reported cases of Cryptosporidium during 2012-15 ranged from 18-25 and reached 43 cases in 2016. Reported Giardia cases during 2012-15 ranged from 170-219 and in 2016 reached 253 cases. Seattle, the most populated city in King County, uses protected water sources and heavily treats drinking water before distribution, resulting in negligible parasite prevalence, suggesting sources other than drinking water may cause infection. To date, no studies have assessed risk associated with the levels present in natural recreational waters of Seattle. My research adapts a Bag-Mediated Filtration System (BMFS) to use Envirochek® HV filters which are processed using Environmental Protection Agency (EPA) 1623.1 methodology to detect and enumerate oocysts and cysts. Quantitative PCR (qPCR) was also used to identify the source of oocysts and cysts. Twelve-liter water samples from 6 recreational beaches in N. Seattle were taken from July 2017 through November 2018 and filtered on-site using the BMFS. Filters were eluted, eluates re-concentrated, purified and analyzed by immunofluorescent microscopy. The oocysts were scraped from the slide and underwent DNA extraction and qPCR for species-typing following established methods. Preliminary results show 2/6 locations and 14% of all samples were positive for Cryptosporidium during summer months, with levels ranging from 1-2 oocysts. Giardia was detected in 4/6 locations and 31% of all samples during summer, ranging from 1-5 cysts. Both fell to 0 oocysts and cysts in fall. Samples collected before and after a New Years "Polar Bear Plunge" resulted in an increase from 0 to 4 Cryptosporidium oocysts and 0 to 27 Giardia cysts. For all locations, avian feces and human feces were present in at least one of the water samples taken. There was some discordance between the two human assays; however, the majority of samples were concordant. The location with the lowest number of samples positive for avian feces was Matthews Beach (57% of samples) and for human feces was Magnuson Beach (43% of samples). Multiple locations had 100% of samples positive for avian and human feces. Dog feces were present in at least one sample at all locations, but all locations had at least one sample where there was discordance between the two assays. Magnuson Beach was the location with the least number of positive samples (14%) while Carkeek Park had the highest number of positive samples (50%). A Quantitative Microbial Risk Assessment characterizing the risk of infection based on the source of contamination showed that at all locations where organisms were present there was at least an 8.08 in 10,000,000 risk of infection. The scenario with the highest risk estimate was for children swimming after the Polar Bear Plunge, where 95% of those who swam had a probability of ≤9.07 infection per 10,000 primary contact children recreators. None of the scenarios fell above the EPA thresholds of 8/1000 illnesses for freshwater and 19/1000 illness for marine water. URI