The Kato technique (also called the Kato-Katz technique) is a laboratory method for preparing human stool samples prior to searching for parasite eggs, with a qualitative and semi-quantitative diagnosis of intestinal helminthic infestations and intestinal schistosomiasis.
The principle is that people infected with Soil-transmitted helminth infections or intestinal schistosomiasis pass the eggs of the worms through their feces. The published methods of the Kato technique vary in detail. One method of the Kato technique is where the sample feces are pressed through a mesh screen to remove large particles. A portion of sieved sample is then transferred to the hole of a template on a slide. After filling the hole, the template is removed and the remaining sample is covered with a piece of cellophane soaked in glycerol.
The glycerol clears the fecal material from around the eggs. The eggs are then counted and the number calculated per gram of feces. Another method involves staining a sieved fecal sample and examining it under a microscope. The total number of stained eggs are counted and used to calculate the number of eggs per gram.
According to Wikipedia, the Kato technique is now most commonly used for detecting schistosome eggs and it has in the past been used for other helminth eggs as well. The World Health Organization (WHO) recommends community diagnosis using the Kato-Katz technique in areas with moderate to high transmission rates of STH (i.e. where the proportion of infected individuals is >20- >50%) or intestinal schistosomiasis (>10-50%), the recommends. However, where the prevalence of STH is <20%, the specificity of this technique makes it less appropriate, and WHO recommends that more sensitive tools should be used. There are alternative techniques to consider in certain cases, including the Urine-CCA (Circulating Cathodic Antigen) test which allows schistosiamsis to be detected within 20 minutes and replaces the Kato fecal test with a single urine test (similar sensitivity).
Commercially-available Kato-Katz kits contain a roll of cellophane that is cut into small pieces and soaked in methylene blue glycerol solution (not included in the kit) the night before the field work. The cellophane is then placed directly on the feces sample, making the eggs more easily visible and allowing long-term storage of the slides. Unfortunately, according to WHO, the company that supplied the bulk of the cellophane rolls recently discontinued production, resulting in a shortage of kits. However, you can find suppliers of Kato Katz kits and alternatives via www.B2Brazil.com, as the Kato technique is widely used in Brazil and therefore there are suppliers both situated and selling there.