A water contamination incident in Oslo, Norway during October 2007; a basis for discussion of boil-water notices and the potential for post-treatment contamination of drinking water supplies

摘要

Over a 5 day period in October 2007 a boil-water notice was served on the majority of Oslo, capital citynof Norway, as a result of a combination of bacteriological findings (coliforms, intestinal enterococci,nand E. coli), and very low numbers of Cryptosporidium oocysts and Giardia cysts in 10 L water samplesntaken from the water distribution network. The water source had been regularly monitored for thesenparasites and generally found to be negative. Over 460,000 residents were affected by the boil-waternnotice, as were many thousands of businesses.nDespite an extensive outbreak of waterborne giardiasis in Bergen, Norway during 2004/2005,noccurrence of parasites in Norwegian drinking water supplies has apparently continued to benconsidered to be of minimal relevance by Norwegian health authorities. Here we describe thenbackground and occurrence of the episode in Oslo, including the species of Cryptosporidium detected,nand use this event, in conjunction with incidents from other countries, as a basis to discuss thenfollowing issues: 1) under which circumstances should the occurrence of Cryptosporidium oocystsnand Giardia cysts in water supplies trigger the issue of a boil-water notice, and 2) the possibilities andnprobabilities of post-treatment contamination events in the water distribution network.