• Interpreting Diagnostic #Tests for #SARS-CoV-2 | Infectious Diseases | JAMA | JAMA Network

    Using available evidence, a clinically useful timeline of diagnostic markers for detection of #COVID-19 has been devised (Figure). Most of the available data are for adult populations who are not immunocompromised. The time course of #PCR positivity and seroconversion may vary in children and other groups, including the large population of asymptomatic individuals who go undiagnosed without active surveillance. Many questions remain, particularly how long potential immunity lasts in individuals, both asymptomatic and symptomatic, who are infected with SARS-CoV-2.

    #sérologie #immunité

    • point rapide et très complet sur les différents tests disponibles
      (il faut un petit bout de temps pour comprendre le graphique…)

      on apprend ainsi :
      qu’une des règles pour le retour au travail du personnel soignant du CDC est fondée, entre autres, sur une étude portant sur un échantillon de 9 personnes…

      In a study of 9 patients, attempts to isolate the virus in culture were not successful beyond day 8 of illness onset, which correlates with the decline of infectivity beyond the first week. That is in part why the “symptom-based strategy” of the Centers for Disease Control and Prevention (CDC) indicates that health care workers can return to work, if “at least 3 days (72 hours) have passed since recovery defined as resolution of fever without the use of fever-reducing medications and improvement in respiratory symptoms (e.g., cough, shortness of breath); and, at least 10 days have passed since symptoms first appeared.

      ou encore, pour les tests d’anticorps :

      Rapid point-of-care tests for detection of antibodies have been widely developed and marketed and are of variable quality. Many manufacturers do not reveal the nature of antigens used. These tests are purely qualitative in nature and can only indicate the presence or absence of SARS-CoV-2 antibodies.

      … on coopère, mais pas trop…

    • Fast coronavirus tests : what they can and can’t do

      Tests antigéniques notamment, dont la sensibilité en fonction du temps est illustrée par la courbe rouge du graphique, tiré de l’article du JAMA ci-dessus.

      Si l’on fie au graphique, leur manque relatif de sensibilité semble surtout problématique dans les tous premiers jours de la maladie, au moment où le malade est le plus contagieux. Cependant l’article révèle une sensibilité qui peut-être très proche du PCR :

      When used on people who were positive for SARS-CoV-2 in a standard PCR test, Abbott’s antigen assay correctly spotted the virus in 95–100% of cases if the samples were collected within a week of the onset of symptoms.

      Et pour plus de précautions :

      The WHO and the US CDC have [...] advised getting a PCR test if people showing symptoms test negative with a rapid antigen test.