There are many people who become ill and do not seek medical attention. While many that do become ill are not tested. For this reason many foodborne illnesses go undetected. CDC has estimated that for every case of salmonellosis that is actually diagnosed and reported to public heath authorities about 38 more occur. (Mead, 1999)
The infections that are diagnosed are usually by specific laboratory test where the causing organism is identified. The three most common causes are identified by culturing stool samples in the lab and identify the bacteria that grow. By examining the stool under a microscope, parasites can be identified. While viruses are too small to see under a microscope, stools are tested for genetic markers that will indicate if specific virus is present. (Mead, 1999)