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

Particle and Fibre Toxicology

Jennifer Keiser³  Jürg Utzinger¹  Marco Albonico⁴  Shaali M Ame²  Said M Ali²  Benjamin Speich³ 

[1]Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland

[2]Laboratory Division, Public Health Laboratory-Ivo de Carneri, Chake Chake, Tanzania

[3]University of Basel, Basel, Switzerland

[4]Ivo de Carneri Foundation, Milan, Italy

关键词: United Republic of Tanzania;    Faecal egg counts;    False-positive;    Quality control;    Kato-Katz technique;    Diagnosis;    Soil-transmitted helminths;   

Others  :  1147048
DOI  :  10.1186/s13071-015-0702-z

 received in 2014-12-17, accepted in 2015-01-27,  发布年份 2015

【 摘 要 】

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.

【 授权许可】

   
2015 Speich et al.; licensee BioMed Central.

【 图 表 】

Figure 1.

Figure 2.

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