Thread by @ISlovan

Un article dans Science Media Center demande à 3 experts de réagir à l'étude française du JAMA (Matta, Lemogne et al.) concernant les causes du covid long.
#covidlong #apresJ20 @longcovid @apresj20 [thread]
sciencemediacentre.org/expert-reactio…

Sont interrogés :
🔹Dr David Strain, Maître de conférences clinique principal, Université d'Exeter
🔹Prof Kevin McConway, Professeur émérite de statistique appliquée, The Open University
🔹Dr Jeremy Rossman, Maître de conférences honoraire en virologie, Université du Kent
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D. Strain : “It misses a very simple explanation. Whether the participants had COVID or not, there is no doubt that they were experiencing some illness that they attributed to COVID. There are multiple viral illness other than COVID that cause “long symptoms””.
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K. McConway : “This looks as if it’s an interesting study – and indeed it is interesting, but it’s potentially very misleading to take its results at face value.”
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"This could be taken to mean that the presence of these symptoms could be more affected by what people believe happened to them than by what previously happened to them as recorded by a test. That does remain a possibility in the light of these results,
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but it’s very far from being the only possibility."

“One basic issue is that this is an observational study, and it’s never possible to be certain about what causes what in observational studies.
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While that’s always true in any observational study, there are some characteristics of this one that make it a particularly important issue here.”
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"What’s more, in this study, the participants already knew the result of their serology (antibody) test when they were asked the questions about whether they thought they had had Covid previously and about their symptoms."
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"So they are unlikely to be typical of people in the general French population who would, mostly, not have had an antibody test at all. This study therefore makes it difficult to draw general conclusions about how these things might work
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in the French population generally (let alone any other population), or to draw any clear conclusions about cause and effect."
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"Another issue about the general applicability of the findings is that these results are based on findings from a subset of a large population cohort study, that looks at volunteers aged 18-69 from the French population. I do not know all the details of this cohort study,
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the CONSTANCES study, but in general people who volunteer for a study like this, which is explicitly about health, is that they tend to be more interested in matters of health than is the population generally. That’s inevitable – but it could be a particular issue when,
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as here, one is studying something that could possibly depend on people’s attitudes about their own health. Further, the participants in this new piece of research seem not to be particularly typical of the whole CONSTANCES cohort in some ways."
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"There are also issues about the serology test that was used. "

"they rightly acknowledge that the antibody test might, in some cases, not actually correspond to whether people had really been infected. That’s always the case for any diagnostic test of this sort, because
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no such test is perfect. The researchers provide arguments to support their belief that this is not in fact a big problem in this study – but errors in diagnostic test results are often counter-intuitive, and I don’t entirely agree with the researchers’ conclusion."
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"What they don’t do is look at false positives – with the assumptions they make, there would be rather a lot of false positives, in fact about 644 of them, which would be about four in every ten people who test positive for antibodies."
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"I think there could be some issues with the assumptions behind these calculations anyway."

"Then, the researchers do not say where their figure of 4% prevalence of previous infection comes from."
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"In the people actually included in their statistical analysis, a little under 2% had a positive antibody test result. That’s a much lower figure than you would get with 4% prevalence and the stated performance rates."
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"this does indicate that the assumptions behind the performance of the test and about possible misclassification of who was previously infected are unlikely to be correct, and that can feed through into the interpretation of the results."
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"I’m not trying to trash this research. These things are difficult to study and this new study does provide potentially useful information."
"But I don’t feel that this research can give a clear enough indication of how likely this is."
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"The conclusions to the research do suggest that the diagnosis and treatment of people who have this kind of symptom should at least consider other possibilities rather than always assuming everything was directly caused by the virus."
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J. Rossman :
"There are several concerns with this analysis."
"First, a serological test for the presence of COVID-19 antibodies is an unreliable marker for previous infection, and some research in hospitalised patients suggests Long COVID patients can tend
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to have weaker antibody responses".
"In addition, antibody levels diminish over time and the study did not report on the duration between reported infection and the serological test."
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"Furthermore, the authors report that only anosmia (or loss of smell) was associated with a positive serological test, but anosmia tends to be one of the shorter duration symptoms of Long COVID and thus, patients still experiencing anosmia may have been more recently
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infected and thus more likely to have detectable antibody levels."

"“Second, the authors state that having a confirmatory diagnostic test or diagnosis of COVID was only associated with anosmia and not any other Long COVID symptoms. However, in their analysis,
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the authors compare the likelihood of different Long COVID symptoms in people that believe they had been infected but have not had a diagnostic test with those that believe they were infected and had diagnostic confirmation. Thus, the 15 symptom categories the authors
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found to be associated with belief in having previously been infected are present in both patients with a positive diagnostic test and those without. If belief, specifically, was driving Long COVID symptoms, then having that belief confirmed would likely increase
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the odds of having those persistent symptoms. In this study, a confirmatory diagnostic test had no impact on the likelihood of having most Long COVID symptoms, suggesting that belief in having been infected is as accurate as having had a diagnostic test, a result
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that has been seen in other Long COVID studies."

"[The] conclusion [of the study] reiterates a damaging narrative, implying that Long COVID is a psychological disease and that by taking steps to avoid symptom exacerbation patients are effectively
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making themselves sick. This is a narrative that Long COVID patients, advocates, physicians and scientist have been struggling to address in many countries around the world. There are multiple studies that demonstrate the presence of
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persistent physiological symptoms following SARS-CoV-2 infection that are not present in uninfected controls."

Dr David Strain @DocStrain
Kevin McConway @kjm2
Jeremy Rossman (U. du Kent, @UniKent)

poke @sfoucart @pascale_santi @JMarieRenaudin @Food_reward @T_Fiolet