Search tips
Search criteria 


Logo of aemPermissionsJournals.ASM.orgJournalAEM ArticleJournal InfoAuthorsReviewers
Appl Environ Microbiol. 1996 January; 62(1): 47–54.
PMCID: PMC167771

Longitudinal studies of Giardia contamination in two community drinking water supplies: cyst levels, parasite viability, and health impact.


Giardia cyst concentrations were determined in an inventory of 153 raw and 91 chlorinated drinking water samples collected at 86 sites from throughout the western Canadian province of British Columbia. Sixty-four percent of raw water samples were cyst positive (69% of sites). Cyst concentrations were lower in chlorinated than in raw water. The viability of cysts in drinking water samples assessed by infectivity in Mongolian gerbils (Meriones unguiculatus) was decreased in chlorinated water. Two rural communities using Giardia-contaminated surface drinking water sources were selected for longitudinal studies including drinking water testing and serological studies of residents. Three hundred thirty-six raw and treated samples from these communities were collected over 24 months. Cyst concentrations and viability were assessed in a 12-month study of each community. Parasite concentrations were lower in chlorinated water than in raw water in both communities. Cyst concentrations were lower in reservoir-settled water than in raw water. Viability, assessed by animal infectivity and corrected for inoculum, decreased following reservoir settling as well as after chlorination. A bolus or spiking phenomenon of cysts was observed in both community drinking water systems and deserves further study. A striking seasonal pattern was seen in one community but not in the second. The seroprevalence data and number of laboratory-confirmed cases identified in each year-long community study are consistent with the possibility that low-level endemic transmission is occurring.

Full Text

The Full Text of this article is available as a PDF (329K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Addiss DG, Davis JP, Roberts JM, Mast EE. Epidemiology of giardiasis in Wisconsin: increasing incidence of reported cases and unexplained seasonal trends. Am J Trop Med Hyg. 1992 Jul;47(1):13–19. [PubMed]
  • Belosevic M, Faubert GM, MacLean JD, Law C, Croll NA. Giardia lamblia infections in Mongolian gerbils: an animal model. J Infect Dis. 1983 Feb;147(2):222–226. [PubMed]
  • Isaac-Renton JL, Shahriari H, Bowie WR. Comparison of an in vitro method and an in vivo method of Giardia excystation. Appl Environ Microbiol. 1992 May;58(5):1530–1533. [PMC free article] [PubMed]
  • Istre GR, Dunlop TS, Gaspard GB, Hopkins RS. Waterborne giardiasis at a mountain resort: evidence for acquired immunity. Am J Public Health. 1984 Jun;74(6):602–604. [PubMed]
  • LeChevallier MW, Norton WD, Lee RG. Occurrence of Giardia and Cryptosporidium spp. in surface water supplies. Appl Environ Microbiol. 1991 Sep;57(9):2610–2616. [PMC free article] [PubMed]
  • Rose JB, Haas CN, Regli S. Risk assessment and control of waterborne giardiasis. Am J Public Health. 1991 Jun;81(6):709–713. [PubMed]
  • Sauch JF, Flanigan D, Galvin ML, Berman D, Jakubowski W. Propidium iodide as an indicator of Giardia cyst viability. Appl Environ Microbiol. 1991 Nov;57(11):3243–3247. [PMC free article] [PubMed]

Articles from Applied and Environmental Microbiology are provided here courtesy of American Society for Microbiology (ASM)