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

Abstract

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

Possible scenarios of environmental transport, occurrence and fate of helminth eggs in light weight aggregate wastewater treatment systems

“…Indeed, there was no massive outbreak of waterborne helminthiases noticed in Norway. However, a water/ food-borne parasite contamination by protozoan cysts and oocysts was reported (Robertson and Gjerde 2001;Robertson et al 2009). …”

Application of Hybrid Process of Coagulation/Flocculation and Membrane Filtration for the Removal of Protozoan Parasites from Water

“…Improper connections can inject water sources contaminated with domestic sewage on the distribution network. Public or domestic water tanks can be contaminated due to animals' access (Robertson et al, 2009). …”

Boil, Boil, Toil and Trouble: The Trouble With Boil Water Advisories in British Columbia

“…A report by the Technical Advisory Committee indicated that a universal index cannot be created for decision-making with regards to BWAs and other types of public notifications (10). Informed decisions are best made on a case-by-case basis after considering a number of system specific risk factors (10,41). water programs, to those with more than 15 years of experience, the former group mentioned the need to "err on the side of caution" or "take a proactive approach over any potential concern"…”

“…One study on a noncompliant town under a boil water order, qualitatively described the conflicts between the townspeople and regulators in their opposing beliefs and opinions on risk perception (28). If the targeted population is not adhering to the BWA"s advice, then the issuing of a BWA becomes a wasted effort (41). In such situations, health authority officials and water suppliers must be careful, as studies on risk communication indicate that when the public receives advice (such as to boil water or chlorinate) which they oppose, they may lose confidence in or begin to distrust the provider of information (the health authority or water supplier) (59).…”