That paper is better than most in the space, in that it has an actual control group, and there are not huge health/age differences between the populations at baseline. Nonetheless, a few interesting things about that paper that stand out to me:
1) Depression and anxiety are the most common "long covid" symptoms, by far. Even "abnormal breathing" doesn't linger to nearly the same extent (fig 1). In fact, when you look at the co-variate matrices, depression and anxiety stand out as a brightly colored axis for the "long covid" cohort (but not for flu), indicating that many/most "long covid" patients had correlated problems with depression and anxiety that aren't seen in the "long flu" group (fig 3).
2) If you look at the last figure (fig 5), it's obvious that the "long covid" symptoms are enriched in the oldest and sickest patients -- yet the main text doesn't break out these groups explicitly, and instead presents "long covid" symptoms as something equally likely to affect all. That's clearly not true. The authors could easily have done this, but did not.
3) The "long covid" symptoms include the primary disease itself (measurements start on day 1), and drops off by 3 months after diagnosis (fig 1), but the authors try to distract from this by emphasizing the group that develops symptoms at any point in the six months after diagnosis, even if they don't have the corresponding symptom in the first 90 days after infection. In fact, 40% of the people in the "symptoms within six months" cohort do not have symptoms in the first 90 days! The authors try to claim that this is proof of some kind of evolving "network" of symptoms...but ignore the simpler explanation that they're detecting "symptoms" unrelated to the original illness.
Long covid papers often make the mistake of blurring together severe, long-term symptoms with minor or unrelated ones, and mixing old people with young people. The authors here have done little to prevent either class of error. Also, looking at this, you also have to conclude that the "long covid" cohort cannot easily be separated from a group of people struggling with depression and anxiety. Are the symptoms caused by the depression? With symptoms like "fatigue" and "pain", it's quite probable.
> With symptoms like "fatigue" and "pain", it's quite probable.
I'd disagree with this. I'd argue that the causation is equally likely to go the other way. Fatigue is a well-documented symptom of multiple viral infections. And painful auto-immune induced symptoms are well-documented in post-covid patients. And who wouldn't be depressed if they can no longer work or do the activities they usually enjoy because they can't get through a day without running out of energy while they can see everyone else getting back to their normal lives.
Everything in the paper is a correlation, and correlations alone do not imply a causative relationship. Therefore, you can just as plausibly argue that the symptoms cited have nothing to do with covid. That said, there's no reason to believe that people with "long flu" (the control group) would be less likely to experience depression as a result of their lingering symptoms, but that is what is seen. And remember that depression and anxiety are more common than the other symptoms -- they're happening in the absence of other "long covid" symptoms in this cohort.
Does Covid cause depression and anxiety, or are depressed and anxious people more likely show up to the doctor seeking covid treatment? You can't tell from a study like this, but the latter is a simpler explanation, consistent with a radical, society-wide initiative that uprooted people's social structures during the study period.
Also, this:
> painful auto-immune induced symptoms are well-documented in post-covid patients.
Is not true. There is some speculation and self-reporting of symptoms, but it has not been "well documented", or documented at all.
I think the categories and the attributes assigned to them are fuzzy. That said fatigue that is attributed to CFS/ME is not just being tired, it's a whole other level, it is a crushing fatigue. CFS/ME fatigue also has clearly definable characteristics; for example Post-exertional malaise (PEM) that does not occur in depressed people unless they also have CFS/ME. In which case they're probably miscategorized.
1) Depression and anxiety are the most common "long covid" symptoms, by far. Even "abnormal breathing" doesn't linger to nearly the same extent (fig 1). In fact, when you look at the co-variate matrices, depression and anxiety stand out as a brightly colored axis for the "long covid" cohort (but not for flu), indicating that many/most "long covid" patients had correlated problems with depression and anxiety that aren't seen in the "long flu" group (fig 3).
2) If you look at the last figure (fig 5), it's obvious that the "long covid" symptoms are enriched in the oldest and sickest patients -- yet the main text doesn't break out these groups explicitly, and instead presents "long covid" symptoms as something equally likely to affect all. That's clearly not true. The authors could easily have done this, but did not.
3) The "long covid" symptoms include the primary disease itself (measurements start on day 1), and drops off by 3 months after diagnosis (fig 1), but the authors try to distract from this by emphasizing the group that develops symptoms at any point in the six months after diagnosis, even if they don't have the corresponding symptom in the first 90 days after infection. In fact, 40% of the people in the "symptoms within six months" cohort do not have symptoms in the first 90 days! The authors try to claim that this is proof of some kind of evolving "network" of symptoms...but ignore the simpler explanation that they're detecting "symptoms" unrelated to the original illness.
Long covid papers often make the mistake of blurring together severe, long-term symptoms with minor or unrelated ones, and mixing old people with young people. The authors here have done little to prevent either class of error. Also, looking at this, you also have to conclude that the "long covid" cohort cannot easily be separated from a group of people struggling with depression and anxiety. Are the symptoms caused by the depression? With symptoms like "fatigue" and "pain", it's quite probable.