In 2019 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. Recommended test purpose: for surveillance and diagnosis of soil- transmitted helminthiasis and schistosomiasis caused by Schistosoma mansoni, S. intercalatum, S. japonicum and S. mekongi. In 2020 SAGE IVD reviewed additional evidence on the Kato-Katz test (available at: https://iris.who.int/handle/10665/339064) and recommended reversing the conditional listing on the Kato-Katz test, therefore, the Kato-Katz test is fully listed in EDL 3.

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%. A new systematic review by Cools et al. (3), (which was not previously available) was reviewed by SAGE IVD in 2020. The additional evidence provides acceptable performance criteria for soil-transmitted helminths, and favourably compares Kato-Katz for surveillance and diagnosis to new tests.

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 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 in 2019. Additional evidence was reviewed by SAGE IVD in 2020: a 2016 systematic review by Danso-Appiah et al. (1) looked at the accuracy of the Kato-Katz test for detecting schistosomiasis compared with a POC circulatory cathodic antigen (CCA) test. A second 2016 systematic review by Kittur et al. (2) compared the prevalence and intensity of infection of S. mansoni detected by the CCA and Kato-Katz test and found that below 50% prevalence the CCA assay is much more sensitive than the Kato-Katz one. But the authors found that the data are inadequate to precisely define the relationship between CCA and Kato-Katz at lower levels of Kato-Katz prevalence. They concluded that more studies are needed directly comparing the two assays in low-prevalence areas to inform decision-making. A 2019 study by Cools et al. (3) compared performance of the Kato-Katz test with two microscopy tests (MINI Flotac, FecPAKG2) and a quantitative PCR (qPCR) test. The study, which was mentioned in the previous submission, found that the Kato-Katz test performed better than newer microscopy tests but was not as sensitive as qPCR. The authors concluded that the PCR test should be used for decisions about discontinuing deworming programmes.

World Health Organization. (‎2019)‎. The selection and use of essential in vitro diagnostics: report of the second meeting of the WHO Strategic Advisory Group of Experts on In Vitro Diagnostics (‎including the second WHO model list of essential in vitro diagnostics)‎. World Health Organization. https://iris.who.int/handle/10665/329527 ; World Health Organization. (‎2021)‎. The selection and use of essential in vitro diagnostics: report of the third meeting of the WHO Strategic Advisory Group of Experts on In Vitro Diagnostics, 2020 (‎including the third WHO model list of essential in vitro diagnostics)‎. World Health Organization. https://iris.who.int/handle/10665/339064