Disease condition and impact on patients: Soil-transmitted helminths are a group of parasites that are transmitted among humans from faecally contaminated soil. The group is composed of four species: Ascaris lumbricoides, Trichuris trichiura, Necator americanus and Ancylostoma duodenale. The morbidity caused by these organisms results from disturbance of normal nutritional processes, the mechanism of which varies by species but is proportional to the number of worms infecting the host. For this reason, it is important that the diagnostic method measure the intensity of infection. Does the test meet a medical need? As many as 2 billion people are affected by soil-transmitted helminthiasis and intestinal schistosomiasis. How the test is used: The Kato-Katz test is a low-cost, well-known laboratory method for diagnosing the presence and intensity of schistosome and soil- transmitted helminth infections; the two groups of helminths can be identified at the same time. The method involves measurement of a standard quantity of faeces (41 mg), clarification with formalin and observation under a microscope to identify and count the eggs of the different parasites separately. The number of parasite eggs on each microscope slide allows quantification of the number of eggs per gram of faeces as a measure of the intensity of infection. The eggs are much larger than those of other parasites, with a distinct morphology, so that the diagnosis is 100% specific; no tests for its validity have therefore been conducted.

Prevalence: The public health importance of soil-transmitted helminthiasis is due to the large number of people infected – as many as two billion – and the direct and indirect morbidity resulting from infection. Socioeconomic impact: WHO attributed a global loss in 2010 of 3.394 million DALYs due to soil-transmitted helminthiasis, for all ages.

The methods for conducting tests have been described (1) but not evaluated. Regular surveys with the Kato-Katz technique are recommended to assess disease prevalence and determine whether a community intervention is necessary.

The Kato-Katz test was compared with alternatives (MINI Flotac, FecPACK and quantitative PCR) in one WHO collaborating centre, which found that the Kato- Katz thick smear method was equivalent or superior. The main constraint of the test is its poor sensitivity for infections of very low intensity, when only a few eggs are present in faeces, as only 41 mg of faeces are used. In helminthology, however, low-intensity infections are of limited clinical relevance, as helminths do not replicate in the host and low-intensity infections do not necessarily evolve into more severe cases.

A kit of 400 tests costs about US$ 40, and the material is recyclable. Capacity to perform the test is well developed in all endemic countries.

Consent is required to obtain a faecal sample. The test is readily accessible because of its low cost.