Quality control in schistosomiasis programmes

The evaluation of a schistosomiasis control programme requires regular monitoring of the performance of technicians responsible for measuring prevalence rates and intensities of infection; simple quality control measures are the most effective form of monitoring. Quality control of microscopy has usually been carried out immediately after primary examination of fresh microscope specimens or by transport of preserved urine or stool samples to a central laboratory; the first method was impossible in Madagascar, and the second involved severe loss and breakage of specimen containers. A new method involving the transport of dried filters fixed on plastic sheets with adhesive tape was therefore used. Essential requirements of the quality control methods were simplicity, effectiveness, acceptability to field technicians, and the production of results valuable to the control programme. Acceptable limits of error (ALE) were determined by a combination of trial-and-error assessment of technicians' capabilities, and the application of a rule-of-thumb derived from quality control studies in clinical chemistry. Results were prepared in the form of simple 2 x 2 tables and easily understood charts for visual assessment of results. Technicians' work varied from excellent to poor; false negative rates (FNR) were usually higher than false positive rates (FPR) and technicians' field counts of eggs were most often lower than control counts. Control proved very useful in motivating technicians, in maintaining high work standards, and in identifying technicians needing further training.