RESUMEN
In September 2009, the Rensselaer County Department of Health investigated an increase in Giardia duodenalis cases. The epidemiological investigation identified that a source of the illness could be a roadside spring located in the eastern part of the county. Epidemiological and environmental health staff conducted a site visit to the roadside spring and found several concerns. Water samples were collected from the roadside spring and sent to the New York State Department of Health for analysis. The water sample results indicated the presence of empty Giardia cysts. Prevention methods occurred and the roadside spring was destroyed. A total of 36 laboratory-confirmed cases of Giardia were identified from this outbreak that included residents of New York State and Massachusetts.