Indication - Neglected tropical diseases
Kato-Katz faecal smear
Microscope slide examination
First added in 2019
Changed in 2020
For surveillance and diagnosis of soil-transmitted helminthiases and schistosomiasis caused by Schistosoma mansoni, S. intercalatum, S. japonicum, S. mekongi
WHO prequalified or recommended products
ICD11 code: 1F9Z
Summary of evidence evaluation
Evidence of the accuracy of the test is not currently available. A study has been submitted for publication but was not made available to the SAGE IVD.
Summary of SAGE IVD deliberations
The Kato-Katz test has been used for more than 50 years. It is valuable for diagnosis and can be used anywhere, including in rural areas where the disease thrives but where there is limited infrastructure. The method is non-invasive, and the kit does not require a cold chain and can be stored for years in field conditions. Templates, spatulas and sample collection containers can be re-used if washed thoroughly. The sensitivity of the test depends on the intensity of infection, but the specificity is 100%.
SAGE IVD recommendation
The SAGE IVD recommended conditional inclusion on the EDL of the Kato- Katz test, pending submission of evidence of its performance. The Group noted that, although the test is widely used, no evidence was submitted on its performance, applicability or precision. The poor sensitivity of the test precludes its use in elimination settings. A complete submission should also include comparisons with newer tests and evidence for their use. 3rd EDL Edition: Additional evidence to support this listing was provided and reviewed by SAGE IVD. During their third annual meeting (held as a series of remote sessions from June to July 2020), SAGE IVD recommended reversing the conditional listing.
Details of submission from 2020
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.
Public health relevance
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.
WHO or other clinical guidelines relevant to the test
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.
Evidence for clinical usefulness and impact
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.
Evidence for economic impact and/or cost–effectiveness
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.
Ethical issues, equity and human rights issues
Consent is required to obtain a faecal sample. The test is readily accessible because of its low cost.
Helminth control in school-age children: a guide for managers of control programmes, second edition. Geneva: World Health Organization; 2011.