Causa versus predição: história de banhos em rios como fator de risco e preditor da infecção pelo Schistosoma mansoni

The analysis of the relationship between those parameters used to measure risk and those used to measure efficiency of diagnostic or screening tests is used, in this paper, to demonstrate the limitations of the use of risk factors as predictors of outcomes distribution in a population. The issue was illustrated by the study of the association, in children, of reported bathing in rivers by asking children if they bathed in rivers and the occurrence of Schistosoma mansoni infection. This question in the above context is important because it is part of the clinical anamnesis taught in several Brazilian medical schools. However, while the history of bathing in rivers proved to be a high risk factor it was a bad discriminator between infected and non-infected children. This finding is demonstrated to be mainly related to the low frequency of people with a negative history of bathing in rivers. But, in general, it was shown that the use of isolated or grouped risk factors in the prediction of outcomes is possible and desirable. The field of knowledge discussed in this paper is not yet well explored in its conceptual and practical aspects. However, it represents an important point of convergence between the epidemiology of the causes and the epidemiology of the interventions.Através da análise das relações existentes entre as medidas de risco e as medidas de eficiência de testes de diagnóstico ou triagem, são discutidos os problemas e limitações concernentes ao uso de fatores de risco na predição da distribuição de efeitos (infecção, doença, cura) em uma população. Para ilustrar o tema, foi utilizada a associação, em crianças, entre a questão "você já tomou banhos em rios?", muito utilizada em anamneses clínicas ensinadas em diversas escolas médicas do Brasil, e a infecção pelo Schistosoma mansoni. A história de banhos em rios, enquanto um importante fator de risco, mostrou-se mau preditor da ocorrência da infecção esquistossomótica. A análise demonstrou que este achado é, em grande parte, devido a baixa freqüência de história negativa de banhos em rios. Porém, a possibilidade da utilização de fatores de risco isoladamente ou agrupados, com o objetivo de predição de efeitos, é possível e desejável. Apesar de pouco explorado nos seus aspectos práticos ou conceituais, esta área de conhecimento representa um importante ponto de convergência entre a epidemiologia das causas e a epidemiologia das intervenções

La austeridad visita a América Latina: aprendizajes de la reciente experiencia europea sobre el estudio de sus efectos en la salud

Spijker y Gumà buscaron analizar diferencias en la salud autopercibida de participantes según el perfil socioeconómico y la posición en el hogar. La salud autopercibida se midió utilizando encuestas de población realizadas antes (2006) y después (2010 y 2014) de la crisis financiera de 2008. Es una medida que está disponible en todos los países europeos y ha sido utilizada en varias investigaciones. Para América Latina, un punto esencial en esta discusión es aprender, a través de la experiencia reciente europea, las mejores maneras de ofrecer resultados sólidos y convincentes respecto de los efectos dañinos de la austeridad en la salud de la población de la región.Discusión sobre: Spijker J, Gumà J. El efecto de la crisis económica sobre la salud en España según el nivel educativo y la relación con la actividad: ¿importa también la duración de la crisis? Salud Colectiva. 2018;14(4):655-670. doi: 10.18294/sc.2018.129

Within- and between-group regression for improving the robustness of causal claims in cross-sectional analysis

Background: A major objective of environmental epidemiology is to elucidate exposure-health outcome associations. To increase the variance of observed exposure concentrations, researchers recruit individuals from different geographic areas. The common analytical approach uses multilevel analysis to estimate individual-level associations adjusted for individual and area covariates. However, in cross-sectional data this approach does not differentiate between residual confounding at the individual level and at the area level. An approach allowing researchers to distinguish between within-group effects and between-group effects would improve the robustness of causal claims. Methods: We applied an extended multilevel approach to a large cross-sectional study aimed to elucidate the hypothesized link between drinking water pollution from perfluoroctanoic acid (PFOA) and plasma levels of C-reactive protein (CRP) or lymphocyte counts. Using within- and between-group regression of the individual PFOA serum concentrations, we partitioned the total effect into a within- and between-group effect by including the aggregated group average of the individual exposure concentrations as an additional predictor variable. Results: For both biomarkers, we observed a strong overall association with PFOA blood levels. However, for lymphocyte counts the extended multilevel approach revealed the absence of a between-group effect, suggesting that most of the observed total effect was due to individual level confounding. In contrast, for CRP we found consistent between- and within-group effects, which corroborates the causal claim for the association between PFOA blood levels and CRP. Conclusion: Between- and within-group regression modelling augments cross-sectional analysis of epidemiological data by supporting the unmasking of non-causal associations arising from hidden confounding at different levels. In the application example presented in this paper, the approach suggested individual confounding as a probable explanation for the first observed association and strengthened the robustness of the causal claim for the second one

Socioeconomic and environmental determinants of adolescent asthma in urban Latin America: an ecological analysis

The prevalence of asthma is high in urban areas of many Latin-American countries where societies show high levels of inequality and different levels of development. This study aimed to examine the relationship between asthma symptoms prevalence in adolescents living in Latin American urban centers and socioeconomic and environmental determinants measured at the ecological level. Asthma prevalence symptoms were obtained from the International Study of Asthma and Allergies in Childhood (ISAAC) phase III. A hierarchical conceptual framework was defined and the explanatory variables were organized in three levels: distal, intermediate, proximal. Linear regression models weighed by sample size were undertaken between asthma prevalence and the selected variables. Asthma prevalence was positively associated with Gini index, water supply and homicide rate, and inversely associated with the Human Development Index, crowding and adequate sanitation. This study provides evidence of the potential influence of poverty and social inequalities on current wheezing in adolescents in a complex social context like Latin America.A prevalência da asma é alta nas áreas urbanas da América Latina, onde as sociedades exibem altos níveis de desigualdade e diferente grau de desenvolvimento. O objetivo é examinar a relação entre a prevalência de sintomas asmáticos em adolescentes de centros urbanos da América Latina e determinantes socioeconômicos e ambientais medidos no nível ecológico. A prevalência de sintomas asmáticos foi obtida do International Study of Asthma and Allergies in Childhood (ISAAC), fase III. Foi definido um modelo conceitual hierárquico. As variáveis explicativas foram organizadas em três níveis: distal, intermediário, proximal. Ajustaram-se modelos de regressão lineal ponderados pelo tamanho amostral entre prevalência de sintomas asmáticos e variáveis selecionadas. A prevalência da asma foi associada positivamente com índice de Gini, índice de desenvolvimento humano, subministro de água potável, e inversamente com aglomeração e saneamento. Em conclusão, este estudo ecológico fornece evidência da influência da pobreza e da desigualdade social sobre os sintomas asmáticos em adolescentes em um contexto social complexo como o da América Latina