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These results suggest that clinicians and public health officers estimate wrongly the threshold even when using their own subjective estimate of influencing factors. Omitting treatment cost and subjective weight of provoked harm can result in a very low threshold. Sound training in threshold principles and providing tools to correctly assess data might help in making better decisions in tuberculosis in developing countries.

ObjectivesTo evaluate the effect of ivermectin mass drug administration on strongyloidiasis and other soil transmitted helminthiases.MethodsWe conducted a retrospective analysis of data collected in Esmeraldas (Ecuador) during surveys conducted in areas where ivermectin was annually administered to the entire population for the control of onchocerciasis.Data from 5 surveys, conducted between 1990 (before the start of the distribution of ivermectin) and 2013 (six years after the interruption of the intervention) were analyzed. The surveys also comprised areas where ivermectin was not distributed because onchocerciasis was not endemic.Different laboratory techniques were used in the different surveys (direct fecal smear, formol-ether concentration, IFAT and IVD ELISA for Strongyloides stercoralis).ResultsIn the areas where ivermectin was distributed the strongyloidiasis prevalence fell from 6.8% in 1990 to zero in 1996 and 1999. In 2013 prevalence in children was zero with stool examination and 1.3% with serology, in adult 0.7% and 2.7%.In areas not covered by ivermectin distribution the prevalence was 23.5% and 16.1% in 1996 and 1999, respectively. In 2013 the prevalence was 0.6% with fecal exam and 9.3% with serology in children and 2.3% and 17.9% in adults.Regarding other soil transmitted helminthiases: in areas where ivermectin was distributed the prevalence of T. trichiura was significantly reduced, while A. lumbricoides and hookworms were seemingly unaffected.ConclusionsPeriodic mass distribution of ivermectin had a significant impact on the prevalence of strongyloidiasis, less on trichuriasis and apparently no effect on ascariasis and hookworm infections.

Abstract. An epidemiologic field study was conducted in the village of Borbòn in Esmeraldas province in northern Ecuador to compare different parasitologic methods in the diagnosis of infection with the Entamoeba histolytica/ Entamoeba dispar complex. The results of two stool antigen detection assays (the Prospect™ Entamoeba histolytica microplate assay and the E. histolytica II™ assay) were compared with isoenzyme characterization of the amebic isolates. Nearly all (176 of 178, 98.9%) subjects were positive for intestinal parasites on direct microscopic examination, and cysts and/or vegetative forms morphologically consistent with the E. histolytica/E .dispar complex were recorded in 48 of 178 cases (27%). Culture in Robinson's medium was positive for amebic stocks in 89 (50%) of the 178 samples tested. Of the 37 isolates successfully stabilized, cloned, and characterized by zymodeme analysis, seven (18.9%) showed isoenzyme patterns of E. histolytica, whereas 26 (70.3%) showed patterns of E. dispar. The remaining four strains were identified as Entamoeba coli (three isolates; 8.1%) and Dientamoeba fragilis (one strain; 2.7%).The immunochromatographic tests showed different degrees of sensitivity and specificity when compared with isoenzyme characterization as the reference technique. The microplate assay, which does not discriminate between E. histolytica and E.dispar, showed a sensitivity of 54.5% and a specificity of 94% for both these amebic species. In contrast, the second-generation E. histolytica II test had a sensitivity of 14.3% and a specificity of 98.4% for E. histolytica sensu stricto. Our survey clearly demonstrated that more specific and sensitive diagnostic tests, such as stool antigen detection assays and isoenzyme analysis, are needed to establish the actual worldwide distribution of E. histolytica and E. dispar.

Rationale From general practitioners to academic staff, clinicians continue to have difficulties in applying clinical epidemiology in their everyday work. They do not fully understand the logical rules behind the numbers and they do not recognize these rules in their work. We present a new model where the pre-test and the post-test probabilities are converted to log10 of odds, and the likelihood ratio (LR) to its own log10. Methods Following Bayes' theorem, adding the log10LR to the log10 pre-test odds gives the log10 post-test odds, which can easily be represented on a logarithmic scale. In addition, by rounding the log10LR to half the unit, we create classes of discriminative power of tests, close to intuitive estimation. This model generates also a user-friendly diagram, adding considerably to the understanding of Bayes' theorem. We evaluated the effect of the rounding, the current use of the classical model and the acceptability of the new model. Results Rounding 10 disease characteristics to half the unit gives an absolute error of less than half a unit. After six explanations of Bayes' theorem, only 6/16 medical students were capable of answering simple questions about predictive value. When asked about weight of disease characteristics, no one of the 50 clinicians mentioned sensitivity, specificity, predictive value or LR. With the new model, more than 80% of trainees found medical decision making easier to understand and recognized the theory in their practice. Conclusions We conclude that our model of diagnostic clinical epidemiology offers a logical environment for an easy and rapid assessment of the evolution of disease probability with consecutive tests, providing a scientific format for 'qualitative' clinical estimations.