Kato-katz Technique

• Kato-Katz technique


  Used for qualitative and semi-quantitative diagnosis of intestinal helminthic infestations caused by Ascaris lumbricoides, Trichuris trichiura, hookworm, and especially Schistosoma spp.
• WHO has recommended the Kato Katz technique (as the gold standard) in areas with moderate to high transmission rates of soil-transmitted helminths (STH) (i.e. where the proportion of infected individuals is >20 to >50%) or intestinal schistosomiasis (>10-50%). Where the prevalence of STH is <20%, the specificity of this technique makes it less appropriate, and more sensitive tools should be used.
• Kato-Katz Principle


  1. Feces are pressed through a mesh screen to remove large particles

  2. A portion of the sieved sample is transferred to the hole of a template on a slide

  3. The template is removed and the remaining sample is covered with a piece of cellophane soaked in glycerol-malachite green

  4. The eggs are then counted and the number is calculated per gram of feces
• Advantages & disadvantages of Kato-Katz technique

  • Requires between 1 to 2 hours before the glycerin clears the background of the stool smear on the slide for accurate visualization of most helminth eggs
  • Hookworm eggs are difficult to recognize due to over-clearing by glycerin after a few hours
  • Ascaris & Trichuris eggs are visible at any time & hookworm eggs are visible 30 minutes after preparation
  • Ideal time for observing Schistosoma eggs is 24 hours after preparation
  • May not be good for small trematode eggs and of little value in detecting protozoan infections
  • Simplicity, sensitivity, and cost effectiveness of the method
• Parasite intensity


  The number of eggs counted of each STH species per 1 gram of stool
• EPG


  The estimated number of Eggs Per Gram of stool excreted by the examined infected individual
• Materials & Reagents


  • Wooden applicator sticks
  • Screen (stainless steel, nylon or plastic: 60-105 um mesh)
  • Template (stainless steel, plastic, or cardboard)
  • Spatula (plastic)
  • Microscope slides (75 x 25 mm)
  • Hydrophilic cellophane (40-50 μm thick, strips 25 x 30 or 25 x 35 mm in size)
  • Flat-bottom jar with lid, forceps and toilet paper or absorbent tissue
  • Newspaper
  • Glycerol-malachite green solution
• Malachite Green solution & cellophane preparation

  1. Prepare 3% malachite green or methylene blue solution

  2. Prepare 50% glycerol solution

  3. Soak the hydrophilic cellophane in the malachite green-glycerol solution for at least 48 hours before use
• Kato-Katz Procedure


  1. Place a small amount of the fecal sample on a newspaper and press a piece of nylon screen on top

  2. Label a glass slide with the sample number and place a template with hole on the center of a microscope slide

  3. Fill the hole in the template with the sieved fecal material

  4. Carefully lift off the template and place it in a bucket of water mixed with concentrated detergent

  5. Place one piece of cellophane, which has been soaked overnight in glycerol solution, over the fecal sample

  6. Invert the microscope slide and firmly press the sample against the cellophane strip on another microscope slide or on a smooth hard surface to spread the feces in a circle

  7. For all except hookworm eggs, keep the slide for one or more hours at room temperature to clear the fecal material prior to examination under the microscope

  8. Examine the smear systematically and multiply the egg counts by the appropriate factor to give the number of eggs per gram of feces
• Ascaris lumbricoides and Trichuris trichiura eggs will remain visible and recognizable for many months, while hookworm eggs clear rapidly and will no longer be visible after 30-60 minutes. Schistosome eggs may be recognizable for up to several months but it is preferable to examine the slide preparations within 24 hours.
• Classes of intensity for schistosome and soil-transmitted helminth infections

  • Light-intensity infections
  • Moderate-intensity infections
  • Heavy-intensity infections