Reviewed by Dr. Lucy Ochola, Head of Tropical & Infectious Diseases , IPR

Kato-Katz was developed in 1954 by the Japanese physician Dr. Kan Kato together with his adviser Dr. Momoshige Miura, a renowned Japanese medical researcher and psychiatrist. The technique was modified for use in field studies in 1972 by a Brazilian team of researchers led by the Brazilian parasitologist, Naftale Katz. The modification technique was adopted by the World Health Organization (WHO) as a gold standard for multiple helminth (parasitic worms) infections.

When you talk about Kato-Katz technique I want  you to think of this:-

Yes, a tea strainer!!  Visualize making tea using the tea leaves,you boil water, put in tea leaves then use a sieve to collect the liquid.  In Kiswahili the tea strainer is called Kichungi. Relating lab work to kitchen work might be awkward but hey we got to relate things by using what we see every day. This way it starts making sense.

Kato-Katz is a widely used method for diagnosing soil-transmitted helminth infections ( caused by parasitic worms) in epidemiological surveys. It is used for qualitative and semi-quantitative diagnosis of intestinal helminthic infestations; caused by Ascaris lumbricoides, Trichuris trichiura, hookworm and especially  Schistosoma spp.

People infected with helminth infections pass the eggs of the worms through their faeces.  In the Kato-Katz technique, faeces are pressed through a mesh screen to remove large particles. Remember the tea strainer! Kato- Katz uses the same concept, the mesh screen/sieve does the same job here;filter out the large debris that is not needed and the residue may contain eggs. The rest of the procedure will be explained in the video below. We always use a mesh screen/sieve during this procedure.

Kato- Katz Pros and Cons

An accurate diagnosis is important for the identification of infected individuals, for assessing anthelminthic drug efficacy, and for monitoring the control and elimination of soil transmitted helminthiasis. However, in settings with low prevalence where it is challenging to identify infected individuals, false-positive results might influence treatment allocation, results of epidemiological studies and monitoring of control programs. Although it is a widely used technique, it has limitations in terms of sensitivity, especially in low-intensity settings. The sensitivity of the Kato-Katz technique is increased by analyzing multiple thick smears from a single or, ideally, from multiple stool samples. While false-negative results can be corrected to some extent by examining multiple Kato Katz thick smears, the probability of false-positive results increases as a function of examining multiple Kato-Katz thick smears. Hence, in studies where multiple Kato-Katz thick smears are examined from each participant, the false-positive rate per individual might not be negligible.

Furthermore, routinely used Kato-Katz thick smear assay is facile and highly specific. Nevertheless, it shows limited sensitivity in low intensity infections and it is unsuitable for assessment of the effect of mass drug administration on prevalence and infection intensity. An accurate and convenient method is therefore essential to ensure a reliable diagnosis of schistosomiasis in the field even for low-intensity infections in order to monitor the success of treatment and to evaluate control programs. Polymerase chain reaction (PCR) might prove to be useful especially in circumstances of lower intensity or prevalence of infection, a condition for which the parasitologic examination shows a well-documented limitation of its sensitivity.

Also, high sensitivity of a single FLOTAC examination for diagnosing common soil-transmitted helminth infections has been confirmed, but fecal egg counts are consistently lower when compared to the Kato-Katz method. With regard to soil-transmitted helminth diagnosis, a study conducted confirmed that a single FLOTAC is more sensitive than multiple Kato-Katz thick smears for the detection of hookworm, Ascaris lumbricoides, and Trichuris trichiura eggs in fecal sample. For hookworm detection   using Kato-Katz techniques, the slides should be read within 30–60 minutes. After that time, the hookworm eggs disappear.

From a scientific point of view, the method with the highest sensitivity and specificity should be used as a diagnostic test. Although real-time PCR has a very good sensitivity and the highest specificity among the currently  used tests, this method is only partially suitable for application in the field. The biggest drawback is the required equipment. In addition, special trained personnel are necessary to carry out the test. Nevertheless, real-time PCR might be a useful additional tool to verify the standard methods or to detect light infections of S. mansoni. New diagnostic tools are therefore required to complement or replace the currently recommended Kato-Katz method.

Enough of writing let’s get to watching. Here is a video showing how to do a Kato-Katz technique. 

REFERENCES:

Utzinger J, Booth M, N'Goran EK, Muller I, Tanner M, Lengeler C, 2001. Relative contribution of day-to-day and intra-specimen variation in faecal egg counts of Schistosoma mansoni before and after treatment with praziquantel. Parasitology 122: 537-44.

Speich B, Ali SM, Ame SM, Albonico M, Utzinger J, Keiser J, 2015. Quality control in the diagnosis of Trichuris trichiura and Ascaris lumbricoides using the Kato-Katz technique: experience from three randomised controlled trials. Parasit Vectors 8: 82.

 He P, Song L-g, Xie H, Liang J-y, Yuan D-y, Wu Z-d, Lv Z-y, 2016. Nucleic acid detection in the diagnosis and prevention of schistosomiasis. Infectious Diseases of Poverty 5: 25.

Fuss A, Mazigo HD, Tappe D, Kasang C, Mueller A, 2018. Comparison of sensitivity and specificity of three diagnostic tests to detect Schistosoma mansoni infections in school children in Mwanza region, Tanzania. PLoS One 13: e0202499.

Pontes LA, Oliveira MC, Katz N, Dias-Neto E, Rabello A, 2003. Comparison of a polymerase chain reaction and the Kato-Katz technique for diagnosing infection with Schistosoma mansoni. Am J Trop Med Hyg 68: 652-6.

Glinz D, Silue KD, Knopp S, Lohourignon LK, Yao KP, Steinmann P, Rinaldi L, Cringoli G, N'Goran EK, Utzinger J, 2010. Comparing diagnostic accuracy of Kato-Katz, Koga agar plate, ether-concentration, and FLOTAC for Schistosoma mansoni and soil-transmitted helminths. PLoS Negl Trop Dis 4: e754.

A special thanks to Collins Ngudi for taking me through this procedure.Below is a Kato Katz procedure video.