title: Changes in Escherichia coli to Cryptosporidium ratios for various fecal pollution sources and drinking water intakes.
abstract: Assessing the presence of human pathogenic Cryptosporidium oocysts in surface water remains a significant water treatment and public health challenge. Most drinking water suppliers rely on fecal indicators, such as the well-established Escherichia coli (E. coli), to avoid costly Cryptosporidium assays. However, the use of E. coli has significant limitations in predicting the concentration, the removal and the transport of Cryptosporidium. This study presents a meta-analysis of E. coli to Cryptosporidium concentration paired ratios to compare their complex relationships in eight municipal wastewater sources, five agricultural fecal pollution sources and at 13 drinking water intakes (DWI) to a risk threshold based on US Environmental Protection Agency (USEPA) regulations. Ratios lower than the USEPA risk threshold suggested higher concentrations of oocysts in relation to E. coli concentrations, revealing an underestimed risk for Cryptosporidium based on E. coli measurements. In raw sewage (RS), high ratios proved E. coli (or fecal coliforms) concentrations were a conservative indicator of Cryptosporidium concentrations, which was also typically true for secondary treated wastewater (TWW). Removals of fecal indicator bacteria (FIB) and parasites were quantified in WWTPs and their differences are put forward as a plausible explanation of the sporadic ratio shift. Ratios measured from agricultural runoff surface water were typically lower than the USEPA risk threshold and within the range of risk misinterpretation. Indeed, heavy precipitation events in the agricultural watershed led to high oocyst concentrations but not to E. coli or enterococci concentrations. More importantly, ratios established in variously impacted DWI from 13 Canadian drinking water plants were found to be related to dominant fecal pollution sources, namely municipal sewage. In most cases, when DWIs were mainly influenced by municipal sewage, E. coli or fecal coliforms concentrations agreed with Cryptosporidium concentrations as estimated by the meta-analysis, but when DWIs were influenced by agricultural runoff or wildlife, there was a poor relationship. Average recovery values were available for 6 out of 22 Cryptosporidium concentration data sets and concomitant analysis demonstrated no changes in trends, with and without correction. Nevertheless, recovery assays performed along with every oocyst count would have enhanced the precision of this work. Based on our findings, the use of annual averages of E. coli concentrations as a surrogate for Cryptosporidium concentrations can result in an inaccurate estimate of the Cryptosporidium risk for agriculture impacted drinking water intakes or for intakes with more distant wastewater sources. Studies of upstream fecal pollution sources are recommended for drinking water suppliers to improve their interpretation of source water quality data.
authors.affiliation: Polytechnique Montréal, Département des Génies Civil, Géologique et des Mines, CP 6079, Succ. Centre-ville, Montréal, Québec, Canada H3C 3A7; Centre INRS-Institut Armand-Frappier, Institut National de Recherche Scientifique (INRS), 531 Boulevard des Prairies, Laval, Québec, Canada H7V 1B7. Electronic address: cindy.lalancette@polymtl.ca.
authors.forename: Cindy
authors.initials: C
authors.lastname: Lalancette
authors.affiliation: Polytechnique Montréal, Département des Génies Civil, Géologique et des Mines, CP 6079, Succ. Centre-ville, Montréal, Québec, Canada H3C 3A7.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Papineau
authors.affiliation: Centre INRS-Institut Armand-Frappier, Institut National de Recherche Scientifique (INRS), 531 Boulevard des Prairies, Laval, Québec, Canada H7V 1B7.
authors.forename: Pierre
authors.initials: P
authors.lastname: Payment
authors.affiliation: Polytechnique Montréal, Département des Génies Civil, Géologique et des Mines, CP 6079, Succ. Centre-ville, Montréal, Québec, Canada H3C 3A7.
authors.forename: Sarah
authors.initials: S
authors.lastname: Dorner
authors.affiliation: Écologie des Systèmes Aquatiques, Université Libre de Bruxelles, Campus de la Plaine, CP 221, Boulevard du Triomphe, B-1050 Bruxelles, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Servais
authors.affiliation: Polytechnique Montréal, Département des Génies Civil, Géologique et des Mines, CP 6079, Succ. Centre-ville, Montréal, Québec, Canada H3C 3A7.
authors.forename: Benoit
authors.initials: B
authors.lastname: Barbeau
authors.affiliation: University of Texas-Houston School of Public Health, Center for Infectious Diseases, El Paso Regional Campus, 1101 N. Campbell CH 412, El Paso, TX 79902, United States.
authors.forename: George D
authors.initials: GD
authors.lastname: Di Giovanni
authors.affiliation: Polytechnique Montréal, Département des Génies Civil, Géologique et des Mines, CP 6079, Succ. Centre-ville, Montréal, Québec, Canada H3C 3A7.
authors.forename: Michèle
authors.initials: M
authors.lastname: Prévost
mesh_terms: D003458:Cryptosporidium / Q000302:isolation & purification*; D060766:Drinking Water / Q000382:microbiology*; D004926:Escherichia coli / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D018508:Water Purification
chemical_list: D060766:Drinking Water
keywords: Cryptosporidium; Drinking water; Escherichia coli; Fecal indicators; Fecal pollution; Source water