Monitoring of Cryptosporidium and Giardia river contamination in Paris area Ce ´line Mons 1 , Aure ´lien Dume `tre 1 , Sylvie Gosselin, Christelle Galliot, Laurent Moulin* CRECEP, Centre de recherche d’expertise et de contro ˆle des eaux de Paris, 144 Avenue Paul Vaillant-Couturier, 75014 Paris, France article info Article history: Received 4 January 2008 Received in revised form 29 September 2008 Accepted 1 October 2008 Published online 1 November 2008 Keywords: Cryptosporidium Giardia Surface water Drinking water Bacterial indicators Rainfall abstract This study evaluates the protozoan contamination of river waters, which are used for drinking water in Paris and its surrounding area (about 615 000 m 3 per day in total, including 300 000 m 3 for Paris area). Twenty litre samples of Seine and Marne Rivers were collected over 30 months and analyzed for Cryptosporidium oocysts and Giardia cysts detection according to standard national or international methods. Cryptosporidium oocysts and Giardia cysts were found, respectively, in 45.7% and 93.8% of a total of 162 river samples, with occasional high concentration peaks. A significant seasonal pattern was observed, with positive samples for Cryptosporidium more frequent in autumn than spring, summer and winter, and positive samples for Giardia less frequent in summer. Counts of enterococci and rainfalls were significantly associated with Giardia concentration but not Cryptosporidium. Other faecal bacteria were not correlated with monitored protozoan. Marne seems to contribute mainly to the parasitic contamination observed in Seine. Based on seasonal pattern and rainfall correlation, we hypothesize that the origin of contami- nation is agricultural practices and possible dysfunction of sewage treatment plants during periods of heavy rainfalls. High concentrations of protozoa found at the entry of drinking water plants justify the use of efficient water treatment methods. Treatment performances must be regularly monitored to ensure efficient disinfection according to the French regulations. ª 2008 Elsevier Ltd. All rights reserved. 1. Introduction Cryptosporidium and Giardia are intestinal protozoa causing mild to severe infections in humans upon transmission by drinking water (Fayer et al., 2004). Cryptosporidium oocysts and Giardia cysts are often excreted in large quantities with the faeces of infected animals and humans. Runoff from contaminated soils and sewage treatment plant dysfunction are responsible for water contamination. Oocysts and cysts remain infective for months in environmental waters and are highly resistant to chlorinated disinfectants (Betancourt and Rose, 2004). The mean annual risk of being infected by waterborne Cryptosporidium has been estimated at 6.2% in the French immunocompetent population and 80.7% in the immuno- deficient population (Pouillot et al., 2004). The risk of being infected by Giardia cysts has not been assessed. Waterborne outbreaks of cryptosporidiosis and giardiasis have been infrequently reported in France compared to those in the US and UK (Guyonnet and Claudet, 2002; Dalle et al., 2003; Karanis et al., 2007). Since 2001, French authorities require the monitoring of Cryptosporidium oocysts and Giardia cysts in water supplies and drinking waters (NF T90-455, AFNOR, 2001). * Corresponding author. Tel.: þ33 140847707; fax: þ33 140847709. E-mail address: laurent.moulin@crecep.fr (L. Moulin). 1 These authors contributed equally to this work. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres 0043-1354/$ – see front matter ª 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2008.10.024 water research 43 (2009) 211–217