Chagas disease: Performance analysis of immunodiagnostic tests anti-Trypanosoma cruzi in blood donors with inconclusive screening results

ABSTRACT Background: The screening of Trypanosoma cruzi-infected blood donors using two serological techniques frequently leads to conflicting results. This fact prompted us to evaluate the diagnostic performance of four "in-house" immunodiagnostic tests and two commercially available enzyme-linked immunosorbent assays (ELISAs). Material and Methods: One hundred and seventy-nine blood donors, whose screening for Chagas disease was doubtful, underwent three in-house ELISAs, one in-house immunoblotting test (TESA-blot), and two commercial ELISAs (bioMérieux and Wiener) in an attempt to define the presence or absence of infection. Simultaneously, 29 donors with previous positive results from three conventional serological tests and 30 donors with constant negative results were evaluated. Results: The ELISA-Wiener showed the highest rate in sensitivity (98.92%) and the ELISA-bioMérieux, the highest specificity (99.45%), followed by the TESA-blot, which showed superior performance, with lower false-negative (2.18%) and false-positive (1.12%) rates. In series, the combination composed of the TESA-blot and ELISA-bioMérieux showed slightly superior performance, with trifunctional protein deficiency (TFP) = 0.01%. Conclusion: Our study confirms the high sensitivity and specificity of commercial kits. To confirm the presence or absence of T. cruzi infection, the combination of TESA-blot and ELISA-bioMérieux may be suggested as the best alternative. Individually, the TESA-blot performed the closest to the gold standard; however, it is not commercially available.

Chagas disease: Performance analysis of immunodiagnostic tests anti-Trypanosoma cruzi in blood donors with inconclusive screening results.

BACKGROUND: The screening ofTrypanosoma cruzi-infected blood donors using two serological techniques frequently leads to conflicting results. This fact prompted us to evaluate the diagnostic performance of four "in-house" immunodiagnostic tests and two commercially available enzyme-linked immunosorbent assays (ELISAs). MATERIAL AND METHODS: One hundred and seventy-nine blood donors, whose screening for Chagas disease was doubtful, underwent three in-house ELISAs, one in-house immunoblotting test (TESA-blot), and two commercial ELISAs (bioMérieux and Wiener) in an attempt to define the presence or absence of infection. Simultaneously, 29 donors with previous positive results from three conventional serological tests and 30 donors with constant negative results were evaluated. RESULTS: The ELISA-Wiener showed the highest rate in sensitivity (98.92%) and the ELISA-bioMérieux, the highest specificity (99.45%), followed by the TESA-blot, which showed superior performance, with lower false-negative (2.18%) and false-positive (1.12%) rates. In series, the combination composed of the TESA-blot and ELISA-bioMérieux showed slightly superior performance, with trifunctional protein deficiency (TFP)=0.01%. CONCLUSION: Our study confirms the high sensitivity and specificity of commercial kits. To confirm the presence or absence of T. cruzi infection, the combination of TESA-blot and ELISA-bioMérieux may be suggested as the best alternative. Individually, the TESA-blot performed the closest to the gold standard; however, it is not commercially available.

Entropy Analysis of High-Definition Transcranial Electric Stimulation Effects on EEG Dynamics.

A foundation of medical research is time series analysis-the behavior of variables of interest with respect to time. Time series data are often analyzed using the mean, with statistical tests applied to mean differences, and has the assumption that data are stationary. Although widely practiced, this method has limitations. Here we present an alternative statistical approach with sample analysis that provides a summary statistic accounting for the non-stationary nature of time series data. This work discusses the use of entropy as a measurement of the complexity of time series, in the context of Neuroscience, due to the non-stationary characteristic of the data. To elucidate our argument, we conducted entropy analysis on a sample of electroencephalographic (EEG) data from an interventional study using non-invasive electrical brain stimulation. We demonstrated that entropy analysis could identify intervention-related change in EEG data, supporting that entropy can be a useful "summary" statistic in non-linear dynamical systems.

Using Software R in research in occupational therapy / Utilização do Software R em pesquisas na terapia ocupacional

Abstract In this paper, it is presented a simple guide for researchers in occupational therapy to perform basic statistical analysis in a flexible and independent way, using the R software, that is a free open source software which its popularity has been increased considerably in many fields. We have presented a step-by-step guide about how to install such software, it is also discussed the necessary steps to include the data set and perform basic statistical analysis, such as the calculation of sample size, basic statistics, graphical presentation, hypothesis tests, and the linear correlation test. The dataset considered in this study comes from a research in occupational therapy and the topics considered are result of the common statistical procedures that were face in the course of the Post Graduation Program in Occupational Therapy at the Federal University of São Carlos (UFSCar), in which were possible to find the principal statistical procedures used by the researchers in applications.

Resumo O presente artigo tem como objetivo fornecer subsídios para que pesquisadores em terapia ocupacional possam realizar procedimentos de estatística básica de maneira mais flexível e independente, a partir do sistema R, um software livre e gratuito, cuja popularidade vem aumentando consideravelmente no âmbito acadêmico. Apresentar-se-á, assim, o passo a passo de como instalar e utilizar o programa na realização de leitura e sumarização de dados, bem como no cálculo de estatísticas básicas, nas representações gráficas de dados quantitativos e qualitativos, no cálculo do tamanho amostral e na efetuação de testes de hipóteses e de teste de correlação linear. O banco de dados utilizado nas demonstrações apresentadas é oriundo de uma pesquisa em terapia ocupacional e as análises aqui realizadas resultam de uma demanda compreendida no decorrer de uma disciplina obrigatória do Programa de Pós-Graduação em Terapia Ocupacional da Universidade Federal de São Carlos (UFSCar), por meio da qual foipossívellevantarosprincipaisprocedimentosestatísticosutilizadospelospesquisadoresemsuaspesquisas.

Performance of six diagnostic tests to screen for Chagas disease in blood banks andprevalence of Trypanosoma cruzi infection among donors with inconclusive serologyscreening based on the analysis of epidemiological variables.

OBJECTIVE: The frequent occurrence of inconclusive serology in blood banks and the absence of a gold standard test for Chagas'disease led us to examine the efficacy of the blood culture test and five commercial tests (ELISA, IIF, HAI, c-ELISA, rec-ELISA) used in screening blood donors for Chagas disease, as well as to investigate the prevalence of Trypanosoma cruzi infection among donors with inconclusive serology screening in respect to some epidemiological variables. METHODS: To obtain estimates of interest we considered a Bayesian latent class model with inclusion of covariates from the logit link. RESULTS: A better performance was observed with some categories of epidemiological variables. In addition, all pairs of tests (excluding the blood culture test) presented as good alternatives for both screening (sensitivity > 99.96% in parallel testing) and for confirmation (specificity > 99.93% in serial testing) of Chagas disease. The prevalence of 13.30% observed in the stratum of donors with inconclusive serology, means that probably most of these are non-reactive serology. In addition, depending on the level of specific epidemiological variables, the absence of infection can be predicted with a probability of 100% in this group from the pairs of tests using parallel testing. CONCLUSION: The epidemiological variables can lead to improved test results and thus assist in the clarification of inconclusive serology screening results. Moreover, all combinations of pairs using the five commercial tests are good alternatives to confirm results.

Performance of six diagnostic tests to screen for Chagas disease in blood banks and prevalence of Trypanosoma cruzi infection among donors with inconclusive serology screening based on the analysis of epidemiological variables

OBJECTIVE: The frequent occurrence of inconclusive serology in blood banks and the absence of a gold standard test for Chagas'disease led us to examine the efficacy of the blood culture test and five commercial tests (ELISA, IIF, HAI, c-ELISA, rec-ELISA) used in screening blood donors for Chagas disease, as well as to investigate the prevalence of Trypanosoma cruzi infection among donors with inconclusive serology screening in respect to some epidemiological variables. METHODS: To obtain estimates of interest we considered a Bayesian latent class model with inclusion of covariates from the logit link. RESULTS: A better performance was observed with some categories of epidemiological variables. In addition, all pairs of tests (excluding the blood culture test) presented as good alternatives for both screening (sensitivity > 99.96% in parallel testing) and for confirmation (specificity > 99.93% in serial testing) of Chagas disease. The prevalence of 13.30% observed in the stratum of donors with inconclusive serology, means that probably most of these are non-reactive serology. In addition, depending on the level of specific epidemiological variables, the absence of infection can be predicted with a probability of 100% in this group from the pairs of tests using parallel testing. CONCLUSION: The epidemiological variables can lead to improved test results and thus assist in the clarification of inconclusive serology screening results. Moreover, all combinations of pairs using the five commercial tests are good alternatives to confirm results.

Bayesian estimation of performance measures of cervical cancer screening tests in the presence of covariates and absence of a gold standard.

In this paper we develop a Bayesian analysis to estimate the disease prevalence, the sensitivity and specificity of three cervical cancer screening tests (cervical cytology, visual inspection with acetic acid and Hybrid Capture II) in the presence of a covariate and in the absence of a gold standard. We use Metropolis-Hastings algorithm to obtain the posterior summaries of interest. The estimated prevalence of cervical lesions was 6.4% (a 95% credible interval [95% CI] was 3.9, 9.3). The sensitivity of cervical cytology (with a result of >or= ASC-US) was 53.6% (95% CI: 42.1, 65.0) compared with 52.9% (95% CI: 43.5, 62.5) for visual inspection with acetic acid and 90.3% (95% CI: 76.2, 98.7) for Hybrid Capture II (with result of >1 relative light units). The specificity of cervical cytology was 97.0% (95% CI: 95.5, 98.4) and the specificities for visual inspection with acetic acid and Hybrid Capture II were 93.0% (95% CI: 91.0, 94.7) and 88.7% (95% CI: 85.9, 91.4), respectively. The Bayesian model with covariates suggests that the sensitivity and the specificity of the visual inspection with acetic acid tend to increase as the age of the women increases. The Bayesian method proposed here is an useful alternative to estimate measures of performance of diagnostic tests in the presence of covariates and when a gold standard is not available. An advantage of the method is the fact that the number of parameters to be estimated is not limited by the number of observations, as it happens with several frequentist approaches. However, it is important to point out that the Bayesian analysis requires informative priors in order for the parameters to be identifiable. The method can be easily extended for the analysis of other medical data sets.

Bayesian estimation of diagnostic tests accuracy for semi-latent data with covariates.

The performance of a diagnostic test is usually summarized by its sensitivity and specificity. Sensitivity is the probability of a positive result, once the individual is truly ill, and specificity is the probability of a negative result, regarding a healthy individual. These measures are obtained by comparing the test outcome and the results of a reference test generically denominated gold standard. However, in many applied problems considering two diagnostic tests, the gold standard is not available for those individuals with negative results on both tests. In addition, not all diagnostic tests have the same performance across different populations. In this context, we present a Bayesian inference approach for performance measures estimation and we propose an extension of this procedure involving the inclusion of covariates. This Bayesian approach is based on Markov Chain Monte Carlo methods. The conditional dependence between the diagnostic tests was considered. As an example, we applied the proposed methodology to a real data set obtained from the medical literature.

A curva ROC para testes diagnósticos / Analysis of diagnostic tests using ROC curves

Métodos estatísticos aplicados à medicina diagnóstica sofreram, nas últimas décadas, enormes avanços. Grande parte destes métodos está voltada ao problema de classificar indivíduos em grupos, sendo que os testes diagnósticos compöem o principal exemplo. Estes testes säo descritos como métodos teoricamente capazes de indicar a presença ou ausência de uma determinada doença, com uma certa chance de erro. A quantificaçäo destas chances de erro é, basicamente, o objetivo destes métodos estatísticos. A probabilidade de um teste diagnóstico produzir um resultado positivo, dado que o indivíduo é portador da doença, é chamada sensibilidade do teste; e a probabilidade do teste produzir um resultado negativo, dado que o indivíduo näo é portador da doença, é chamada especificidade. O presente estudo objetiva descrever a situaçäo onde o teste produz uma resposta que näo é descrita simplesmente como "positivo" ou "negativo", mas por um resultado que pode ser expresso por uma variável categórica ordinal ou por uma variável contínua. O desempenho de um teste assim descrito em auxiliar diagnósticos clínicos é usualmente demonstrado pela curva ROC (receiver operating characteristic). Säo descritos neste estudo métodos comumente utilizados para estimar a curva ROC, o efeito da tendenciosidade devida à verificaçäo, a utilidade da área sob a curva ROC, o problema da comparaçäo entre duas curvas e os métodos de geraçäo de regiöes de confiança para a curva ROC. Dois exemplos reais em oncologia ilustram o uso da curva ROC.

Modelos em análise de sobrevivência / Survival analysis models

Neste artigo apresentamos diferentes modelos utilizados em análise da sobrevivência, discutimos as dificuldades envolvidas na análise estatística deste tipo de conjunto de dados. aspectos importantes como presença de censuras e variáveis explicativas nos dados. Aspectos importantes como presença de censuras e variáveis explicativas nos dados, riscos competitivos e vários eventos para cada indivíduo säo considerados. A modelagem através da funçäo de risco é discutida e modelos baseados nesta funçäo säo apresentados e comparados. É enfatizada a evoluçäo dos mesmos a partir de Cox (1972)