05-14-2020, 09:17 PM
To answer your questions:
It is reasonable to measure IgG than IgM. Whereas IgG provides lasting immunity, IgM is only indicative of recent infection and then fades. The downside of using IgG is that it turns positive later than IgM.
The prevalence estimates were made by assigning each participant in the study a weight inversely proportional to their probability of being included in the study (inverse probability weighting), further adjusting for the likelihood of non-response by sex and age. Because of the complex study design, all analyses take into account the effect of stratification by province and city size, and clustering by household and census tract to determine the standard error and corresponding confidence interval.
On that basis, it doesn't sound like they adjusted for sensitivity or specificity. Note that the study itself reran the test characteristics and found:
En estudios de fiabilidad realizados para ENE-Covid19 se comunicó una sensibilidad del 73% y del 79% respectivamente para IgM o IgG, y una sensibilidad del 85% considerando positividad en cualquiera de los isotipos, con una especificidad del 98% para IgM y del 100% para IgG.
IgM: 73% sensitivity, 98% specificity
IgG: 79% sensitivity, 100% specificity
IgG or IgM: 85% sensitivity [and by definition, would have 98% specificity]
One last thing
In order to determine SARS-CoV-2 antibodies they decided to use two types of tests, a rapid immunochromatography test (the one reported), which allowed them two obtain results immediately to allow the participants to learn of their results and avoids venopuncture, and, in the participants who consented to giving a blood sample, a test for IgG antibodies by means of an immunoassay, which would function as their gold standard. Elsewhere in the report they state that they don't have all the results from the immunoassay. However, in the 16,953 samples they did run, the concordence is 97.3%.
BC
BC
It is reasonable to measure IgG than IgM. Whereas IgG provides lasting immunity, IgM is only indicative of recent infection and then fades. The downside of using IgG is that it turns positive later than IgM.
Quote:Las estimaciones de la tasa de seroprevalencia por COVID-19 se realizan asignando a cada participante del estudio un peso de muestreo inversamente proporcional a su probabilidad de selección, ajustado adicionalmente por la tasa de no respuesta específica según sexo y grupo de edad. Debido al diseño complejo del estudio, todos los análisis tienen en cuenta tanto el efecto de la estratificación por provincia y tamaño municipal, como el efecto de la agrupación por hogares y secciones censales, en el error estándar de la tasa estimada de seroprevalencia y en su correspondiente intervalo de confianza.
The prevalence estimates were made by assigning each participant in the study a weight inversely proportional to their probability of being included in the study (inverse probability weighting), further adjusting for the likelihood of non-response by sex and age. Because of the complex study design, all analyses take into account the effect of stratification by province and city size, and clustering by household and census tract to determine the standard error and corresponding confidence interval.
On that basis, it doesn't sound like they adjusted for sensitivity or specificity. Note that the study itself reran the test characteristics and found:
En estudios de fiabilidad realizados para ENE-Covid19 se comunicó una sensibilidad del 73% y del 79% respectivamente para IgM o IgG, y una sensibilidad del 85% considerando positividad en cualquiera de los isotipos, con una especificidad del 98% para IgM y del 100% para IgG.
IgM: 73% sensitivity, 98% specificity
IgG: 79% sensitivity, 100% specificity
IgG or IgM: 85% sensitivity [and by definition, would have 98% specificity]
One last thing
Quote:Para la medición de anticuerpos anti SARS-Cov-2 decidimos utilizar dos tipos de test: incluye un test rápido de inmunocromatografía, que permite obtener resultados in situ para el conocimiento de los participantes y evita la venopunción y, en los participantes que accediesen a donar una muestra de sangre, una determinación de anticuerpos IgG mediante inmunoensayo, dentro de las técnicasactualmente disponibles esta determinación sería nuestro gold-standard.
In order to determine SARS-CoV-2 antibodies they decided to use two types of tests, a rapid immunochromatography test (the one reported), which allowed them two obtain results immediately to allow the participants to learn of their results and avoids venopuncture, and, in the participants who consented to giving a blood sample, a test for IgG antibodies by means of an immunoassay, which would function as their gold standard. Elsewhere in the report they state that they don't have all the results from the immunoassay. However, in the 16,953 samples they did run, the concordence is 97.3%.
BC
BC