Application of Monitoring Data forGiardia andCryptosporidium to Boil Water Advisories

Abstract

Despite the problems associated with analyzing water samples for Giardia cysts and Cryptosporidium oocysts, the data can be very useful if their strengths and weaknesses are understood. Two municipalities in northern Ontario, Temagami and Thunder Bay, both issued boil water advisories for Giardia contamination. Data from these two cities are compared to show that only one municipality experienced a real outbreak, whereas the other did not. The concentration of Giardia cysts was much higher than background during the outbreak at Temagami, and the postoutbreak concentrations of cysts were very similar to the long-term average cyst concentration at Thunder Bay. The waterborne outbreak of giardiasis at Temagami was characterized by consistent positive results from water samples, concentrations two to three orders of magnitude higher than normal, and an obvious increase in the number of cases of giardiasis in the population. No outbreak was experienced at Thunder Bay, but a boil water advisory (BWA) was set in place for more than a year on the basis of a single sample from Loch Lomond in which only two cysts were detected but the sample equivalent volume was low. This gave the impression of a sudden increase in concentration, but 39 of 41 subsequent samples were negative. Additional factors that led to a BWA at Thunder Bay are described, and recommendations are presented to help determine when a BWA is necessary and when it should be rescinded.

Molecular Epidemiology ofCryptosporidiumandGiardiain Humans on Prince Edward Island, Canada: Evidence of Zoonotic Transmission From Cattle

“…The prevalence of 0.05% in our human faecal samples is comparatively lower and suggests that Giardia shedding on PEI is rare. In Canada, several human G. duodenalis outbreaks have been reported in the last two decades (Wallis et al., 2001) with the most predominant genotype being assemblage A (Caccio and Ryan, 2008). The exclusive detection of assemblage A in this study is consistent with the predominant occurrence of this assemblage in Canada.…”

Detection and enumeration of Cryptosporidium oocysts in environmental water samples by Real-time PCR assay

“…It seems that effective levels to outbreaks with these protozoa ordinarily occur when oocyst concentrations raised to 5 Giardai cyst in 100 liters of water sampled (4,5) and 10 to 30 oocysts for Cryptosporidium (6). Detection of low numbers of organisms in water samples is difficult, it needs very sensitive techniques.…”

Population-based laboratory surveillance for Giardia sp. and Cryptosporidium sp. infections in a large Canadian health region

“…These infections are associated with endemic infection rates in many jurisdictions but they have also caused large outbreaks [5,6]. In Canada, several outbreaks have been reported in recent decades due to Cryptosporidium parvum [7,8] and Giardia lamblia [9]. Population-based surveillance studies conducted in the United States have demonstrated increasing rates for giardiasis between 1992–97 with the highest national rates being amongst children aged 0–5 years, followed closely by persons aged 31–40 years [1,10-12].…”