Journal Article

Quality control in the diagnosis of Trichuris trichiura and Ascaris lumbricoides using the Kato-Katz technique: experience from three randomised controlled trials

Ali, Said M, Albonico, Marco, Ame, Shaali M, Utzinger, Jürg, Speich, Benjamin, Keiser, Jennifer

2015

Overview

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.

• Publisher: BioMed Central,BioMed Central Ltd,BMC
• Subject: Analysis / Animals / Ascariasis - diagnosis / Ascariasis - parasitology / Ascaris lumbricoides / Ascaris lumbricoides - growth & development / Ascaris lumbricoides - isolation & purification / Biomedical and Life Sciences / Biomedicine / Child / Diagnosis / drugs / Eggs / Entomology / epidemiological studies / Epidemiology / Evaluation / Faecal egg counts / False-positive / fecal egg count / feces / Feces - parasitology / Female / guidelines / helminthiasis / helminths / Humans / Infectious Diseases / Kato-Katz technique / Male / Methods / monitoring / Parasite Egg Count - methods / Parasite Egg Count - standards / Parasitology / patients / probability / Quality Control / Quality management / randomized clinical trials / Soil-transmitted helminths / Tanzania / Trichuriasis - diagnosis / Trichuriasis - parasitology / Trichuris - growth & development / Trichuris - isolation & purification / Trichuris trichiura / Tropical Medicine / Veterinary Medicine/Veterinary Science / Virology / World Health Organization