Occurrence of Cryptosporidium Oocysts and Giardia Cysts in Sewage in Norway

Abstract

Samples of sewage influent from 40 sewage treatment works (STW) throughout Norway were examined for Cryptosporidium oocysts and Giardia duodenalis cysts. Both parasites were detected frequently (80% of STW were Cryptosporidium positive; 93% of STW were Giardia positive) and at maximum concentrations of >20,000 parasites/liter. The data suggest giardiasis is more widespread, and/or occurs with greater infection intensity, than cryptosporidiosis in Norway. STW serving higher person equivalents were more likely to be positive and had higher parasite concentrations. Parasite concentrations were used to estimate the proportion of contributing populations that could be clinically infected. For Cryptosporidium, the highest estimates were up to 5 per 100,000 individuals for two populations in eastern Norway. For Giardia, the highest estimate was 40 infected per 100,000 persons (approximately five times the usual national annual average) contributing to an STW in western Norway. As this population experienced a large waterborne giardiasis outbreak 6 months after sampling, it can be speculated that regular challenge with Giardia may occur here. Most Giardia isolates in sewage influent were assemblage A, although some assemblage B isolates were detected. There was substantial heterogeneity, but most samples contained isolates similar to genotype A3. Removal efficiencies at two STW with secondary treatment processes were estimated to be approximately 50% for Cryptosporidium and >80% for Giardia. An STW with minimal treatment had negligible removal of both parasites. Many STW in Norway have minimal treatment and discharge effluent into rivers and lakes, thus, risk of contamination of water courses by Cryptosporidium and Giardia is considerable. Analysis of sewage influent for Cryptosporidium oocysts andGiardia duodenalis cysts has been used in a variety of studies to further elucidate aspects of the epidemiology, both conventional and molecular, of these parasites in particular populations or geographic regions (1,20). Additionally, such analyses can be used as an indirect method of assessing the occurrence of these infections in human populations (12,17,18). This is particularly useful in situations where it is believed that the occurrence of these infections is underestimated.Investigation of the epidemiology of cryptosporidiosis and giardiasis in human populations in Norway is hampered by lack of submission of fecal samples to diagnostic laboratories. This may be due to low infection rates but is more probably due to lack of awareness of these infections among medical personnel. In the absence of such specimens, investigation of sewage influent for these parasites can provide a useful approach for collecting data on the extent of infection in different regions. However, the method for analyzing such samples must be chosen carefully; particulate debris, fats, and other contaminants from a range of sources mean that standard water analysis procedures are inappropriate. Minimizing sample manipulation procedures has previousl...

Treated Greywater Reuse for Hydroponic Lettuce Production in a Green Wall System: Quantitative Health Risk Assessment

“…The base for the estimate of reference pathogen concentration was the combination of information about E. coli at each treatment step with the concentration of the reference pathogens in the sewage system, which has been published in different studies. Moreover, with 1% of the sewage assumed to be mixed with the greywater system (Table S2), from the previous studies the average concentration of Cryptosporidium, Campylobacter, and Norovirus in the sewage system was estimated to be 678.1 oocysts/100 mL, 118 MPN/100 mL, and 5.1 × 10 4 gene copies/100 mL, respectively [42][43][44]. The concentration of reference pathogens in the irrigation water was dependent on the efficiency of the greywater treatment steps of the system, which was based on E. coli removal efficiency.…”

Treated Greywater Reuse for Hydroponic Lettuce Production in a Green Wall System – Quantitative Health Risk Assessment

“…The base for the estimate of reference pathogen concentration was the combination of information about E. coli in each treatment steps with the concentration of reference pathogens in the sewage system, which was published in different studies. Moreover, 1% of the sewage assumed to be mixed with the greywater system (Table S2), from the previous studies, the average concentration of Cryptosporidium, Campylobacter, and norovirus in the sewage system estimated 678.1 oocysts/100ml, 118 MPN/100ml, and 5.1x10 4 gene copies/100ml respectively [40][41][42]. The concentration of reference pathogens in the irrigation water were dependent on the efficiency of greywater treatment steps of the system, which was based on E. coli removal efficiency.…”

Patógenos e indicadores microbiológicos de calidad del agua para consumo humano

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