Abstract
Animal and human helminth infections are highly prevalent around the world, with only few anthelminthic drugs available. The anthelminthic drug performance is expressed by the cure rate and the egg reduction rate. However, which kind of mean should be used to calculate the egg reduction rate remains a controversial issue. We visualized the distributions of egg counts of different helminth species in 7 randomized controlled trials and asked a panel of experts about their opinion on the egg burden and drug efficacy of two different treatments. Simultaneously, we calculated infection intensities and egg reduction rates using different types of means: arithmetic, geometric, trimmed, winsorized and Hölder means. Finally, we calculated the agreement between expert opinion and the different means. We generated 23 different trial arm pairs, which were judged by 49 experts. Among all investigated means, the arithmetic mean showed poorest performance with only 64% agreement with expert opinion (bootstrap confidence interval [CI]: 60-68). Highest agreement of 94% (CI: 86-96) was reached by the Hölder mean M0.2, followed by the geometric mean (91%, CI: 85-94). Winsorized and trimmed means showed a rather poor performance (e.g. winsorization with 0.1 cut-off showed 85% agreement, CI: 78-87), but they performed reasonably well after excluding treatment arms with a small number of patients. In clinical trials with moderate sample size, the currently recommended arithmetic mean does not necessarily rank anthelminthic efficacies in the same order as might be obtained from expert evaluation of the same data. Estimates based on the arithmetic mean should always be reported together with an estimate, which is more robust to outliers, e.g. the geometric mean.
Highlights
Helminths, including cestodes, nematodes and trematodes, infect a large number of humans and animals
Helminth infections are responsible for decreased productivity, which leads to economic losses for famers [4]
The methods can be divided into four main steps: i) gathering and preparing data from previously conducted randomized multi-arm anthelminthic drug trials and dividing the trial arms into pairs, ii) visualizing the egg count distributions and asking experts for their opinion, which one of the two trial arms has a higher egg burden and better drug efficacy, iii) calculating mean egg counts at baseline and follow-up and egg reduction rates (ERRs) of each trial arm using different types of means, and iv) assessing the performance of each type of mean according to their proportional agreement with the experts
Summary
Helminths, including cestodes, nematodes and trematodes, infect a large number of humans and animals. Helminth infections are highly prevalent with for example, 1.5 billion people infected with soil-transmitted helminths (STHs, Ascaris lumbricoides, hookworm and Trichuris trichiura) [1], 240 million with schistosomes [2] and 120 million with lymphatic filaria [3]. To control human helminth infections, the World Health Organization’s (WHO) goal is to reduce the burden caused by moderate and heavy infections by increasing the coverage of anthelminthic drugs within socalled preventive chemotherapy programs–i.e. annual or biannual mass treatment of high risk populations [5]. Anthelminthic resistance has been observed widely in veterinary medicine [6,7,8]; emergence of resistance in humans is likely [9,10]. It is crucial to closely observe the anthelminthic drug efficacy in order to detect resistance development [11,12]
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