Long Covid is Not One Thing
A new study finds "3" types of the disorder. Actually, more than 3.
Long Covid is heterogenous; it is not one thing. A new study from King’s College in London tries to classify different forms of Long Covid, and there is good food for thought in the study.
“Profiling post-COVID syndrome across different variants of SARS-CoV-2.” MedRxiv, 31 Jul 2022, Full Article.
Two to Eight clusters of patients were identified based on symptoms. Three clusters seem to be recurring or dominant, but it is more complex than that.
The 3 most general and common patterns were identified: Cardiopulmonary, Neurological, and Multi-Organ/Autoimmune.
Different patterns of Long Covid probably have different mechanisms behind them, and the logical next step is to find if there are therapies that are more useful for some of the categories of Long Covid.
Different patterns were seen based on which variant of the SARS2 virus caused the initial infection. Future virus variants may lead to Long Covid patterns that are different from what we have seen so far. (For example, hair loss may be a symptom that was not part of the first two years of infection, but recent reports indicate it may be part of the Omicron variant covid/long-covid.)
These groupings are not fixed in stone, and trying to pigeonhole a person into one or more of them to the exclusion of other symptoms does not make sense.
Here’s an image from the study, documenting five different types of Long Covid seen in people who had the Delta variant of the virus. The red lines on the right of the diagram show 5 different groups that the researchers created for this group of patients. The left of the diagram has labels for different symptoms, and the lines point to different groups where those symptoms were present. The thickness of the colored lines indicates how common a symptom was - Earache was not very common so it gets a thin line, while Anosmia (loss of smell) was very common with the Delta variant, and it gets a thick set of lines.
Note that there is symptom overlap - while a few symptoms are unique to one type of Long Covid, many apply to 2, 3, or even 4 of the classes.
When we make groups and classify things, there is often a degree of subjectivity. If two things are sort of similar, but not exactly the same, should we split them into two groups, or lump them together in one group? It really depends on what our goal is in creating the categories. We might want to have as few groups as is reasonable to simplify the situation (so lump those 2 things together). Or we might want to have as many groups as is practical to try to describe all the different things that are going on (so split those things into separate groups). Generalization is often useful, but it can also lead to faulty reasoning if we aren’t careful.
A few weeks ago, there was a Twitter discussion where some people put forward the idea that Long Covid should be diagnosed using objective biomarkers. I get where they are coming from, but Long Covid is heterogenous - it is not one thing. There is no single marker in the blood or urine that gives an objective indication of whether someone is suffering from it. With time, we will surely find some biomarkers that indicate that a person is suffering from particular types of long covid - but today, we don’t have that type of certainty. Trying to move to such objective markers without a better understanding of LC poses real problems - and in the worse case, it could become a form of minimalization or denial.
The bottom line is that the King’s College study can move us towards better thinking about Long Covid - but only if we digest the study, and use what it contains carefully.