Risk of giardiasis from consumption of wilderness water in North America: A systematic review of epidemiologic data

Objectives: A meta-analytic study was conducted to test the hypothesis that consumption of water from North American backcountry sources poses a statistically significant risk for acquisition of giardiasis. Methods: The biomedical literature was surveyed by accessing Medline, and identified studies were supplemented with references in current reviews, published dissertations, and prior communications with state health departments. Studies were classified by methodologic design and subjected to predetermined inclusion criteria. Odds ratios with 95% confidence intervals, chi-squares, and P-values for epidemiologic surveys were either computed from raw data or abstracted directly from the included studies. Results: Of 104 articles identified in the initial screening, nine met the inclusion criteria. Neither of two case reports met the criteria of the Centers for Disease Control and Prevention (CDC) for waterborne disease outbreak. Two prospective studies were identified, but neither showed a significant association. Of four case- control studies providing data, three reported an odds ratio of greater than one. Conclusions: Published reports of confirmed giardiasis among outdoor recreationists clearly demonstrate a high incidence among this population. However, the evidence for an association between drinking backcountry water and acquiring giardiasis is minimal. Education efforts aimed at outdoor recreationists should place more emphasis on handwashing than on water purification. Further studies should attempt to separate the specific risk factor of drinking water from backcountry sources from other behaviors among this group that may contribute to the risk.