Parasite testing by examination of stool samples will often require multiple samples and the use of a lab that specializes in this type of testing. More comprehensive testing, such as a Comprehensive Digestive Stool Analysis with Parasitology is suggested and available from the same stool sample when bacterial imbalances or digestive problems are suspected. Examples of laboratories offering such services include Meridian Valley Labs and Great Smokies Diagnostic Labs (now called Genova Diagnostics) and more information along with their home pages can be found
here and here.