title: Quality control in the diagnosis of Trichuris trichiura and Ascaris lumbricoides using the Kato-Katz technique: experience from three randomised controlled trials.
abstract: BACKGROUND
  An accurate diagnosis of soil-transmitted helminthiasis is important for individual patient management, for drug efficacy evaluation and for monitoring control programmes. The Kato-Katz technique is the most widely used method detecting soil-transmitted helminth eggs in faecal samples. However, detailed analyses of quality control, including false-positive and faecal egg count (FEC) estimates, have received little attention.
  
  
  METHODS
  Over a 3-year period, within the frame of a series of randomised controlled trials conducted in Pemba, United Republic of Tanzania, 10% of randomly selected Kato-Katz thick smears were re-read for Trichuris trichiura and Ascaris lumbricoides eggs. In case of discordant result (i.e. positive versus negative) the slides were re-examined a third time. A result was assumed to be false-positive or false-negative if the result from the initial reading did not agree with the quality control as well as the third reading. We also evaluated the general agreement in FECs between the first and second reading, according to internal and World Health Organization (WHO) guidelines.
  
  
  RESULTS
  From the 1,445 Kato-Katz thick smears subjected to quality control, 1,181 (81.7%) were positive for T. trichiura and 290 (20.1%) were positive for A. lumbricoides. During quality control, very low rates of false-positive results were observed; 0.35% (n = 5) for T. trichiura and 0.28% (n = 4) for A. lumbricoides. False-negative readings of Kato-Katz thick smears were obtained in 28 (1.94%) and 6 (0.42%) instances for T. trichiura and A. lumbricoides, respectively. A high frequency of discordant results in FECs was observed (i.e. 10.0-23.9% for T. trichiura, and 9.0-11.4% for A. lumbricoides).
  
  
  CONCLUSIONS
  Our analyses show that the rate of false-positive diagnoses of soil-transmitted helminths is low. As the probability of false-positive results increases after examination of multiple stool samples from a single individual, the potential influence of false-positive results on epidemiological studies and anthelminthic drug efficacy studies should be determined. Existing WHO guidelines for quality control might be overambitious and might have to be revised, specifically with regard to handling disagreements in FECs.
authors: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland. benjamin.speich@unibas.ch.|University of Basel, Basel, Switzerland. benjamin.speich@unibas.ch.
authors: Benjamin
authors: B
authors: Speich
authors: Laboratory Division, Public Health Laboratory-Ivo de Carneri, Chake Chake, Tanzania. saidmali2003@yahoo.com.
authors: Said M
authors: SM
authors: Ali
authors: Laboratory Division, Public Health Laboratory-Ivo de Carneri, Chake Chake, Tanzania. shaaliame@yahoo.com.
authors: Shaali M
authors: SM
authors: Ame
authors: Ivo de Carneri Foundation, Milan, Italy. albonico@tin.it.
authors: Marco
authors: M
authors: Albonico
authors: University of Basel, Basel, Switzerland. juerg.utzinger@unibas.ch.|Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland. juerg.utzinger@unibas.ch.
authors: Jürg
authors: J
authors: Utzinger
authors: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland. jennifer.keiser@unibas.ch.|University of Basel, Basel, Switzerland. jennifer.keiser@unibas.ch.
authors: Jennifer
authors: J
authors: Keiser
mesh_terms: D000818:Animals; D001196:Ascariasis / Q000175:diagnosis* / Q000469:parasitology; D017164:Ascaris lumbricoides / Q000254:growth & development / Q000302:isolation & purification*; D002648:Child; D005243:Feces / Q000469:parasitology; D005260:Female; D006801:Humans; D008297:Male; D010270:Parasite Egg Count / Q000379:methods / Q000592:standards; D011786:Quality Control; D013636:Tanzania; D014257:Trichuriasis / Q000175:diagnosis* / Q000469:parasitology; D014258:Trichuris / Q000254:growth & development / Q000302:isolation & purification*
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