This is Fresh Air, I'm Terry Gross. The number of new COVID cases is in steep decline in many parts of the country,

but we don't yet know how many of the people who have had COVID will develop long COVID with chronic symptoms that may include fatigue,

shortness of breath, coughing, joint pain, muscle pain, chest pain, and problems with focus and memory.

The attention researchers are devoting to long COVID may end up benefiting people with mysterious, hard-to-diagnosed diseases, including Lyme disease, and autoimmune diseases like chronic fatigue syndrome and fibromyalgia.

Patients with these diseases have often been told it's all in their heads.

My guest Megan O'Rourke has been writing about long COVID for the Atlantic and Scientific American.

Her new book is about her own experiences with chronic illness. It started in the late 1990s, soon after graduating college.

Her symptoms over the years have included extreme fatigue, brain fog, joint pain, nerve pain that felt like constant electric shocks, hives, fevers, and more.

She's been diagnosed with Lyme disease and several autoimmune diseases and tried many different approaches to treating them.

Her new book, The Invisible Kingdom, Reimagining Chronic Illness, is also a diagnosis of our medical system and how ill-equipped it is to deal with patients who are suffering with illnesses for which we may not even have names yet, let alone treatments.

A work is a former fiction nonfiction editor at the New Yorker, former culture and literary editor at Slate, and is now the editor of the Yale Review.

Megan O'Rourke, welcome to Fresh Air. COVID has been triggering epic rates of long COVID, whose symptoms are very similar to autoimmune diseases, and long COVID seems to be related to immune dysregulation.

Can you compare long COVID with the autoimmune diseases that you write about in your book, that you've experienced? What do they have in common?

Absolutely. So long COVID is characterized by a wide variety of symptoms that persist long after the initial infection with the SARS-CoV-2 virus.

And those symptoms might include chest pain, but they also include so-called vague and subjective symptoms like brain fog or fatigue and roaming pain in the body.

For some patients, these symptoms come and go a little bit. They are also hard to measure on certain kinds of conventional lab tests, and all of this puts pressure on patients who then have to testify to the reality of their own illness.

In this way, it's quite similar to many of the autoimmune diseases and the other diseases I write about in my book, because these are diseases that we lack really good tools for measuring, especially in early states of the disease.

They're diseases that can come and go. They're diseases that can be affected and worsened by stress. And their diseases, therefore, that are often contested by medicine.

You know, we can get into it further, but there's a lot we still don't know about what exactly long COVID is, and a lot of the researchers I've reported on have said to me, the term itself may be an umbrella term in the end that encompasses a few different kinds of conditions that we come to understand.

And in fact, one of those conditions may be autoimmune disease, right? We do have evidence that long COVID seems to be triggering pretty substantial rates of autoimmune disease in some patients who get COVID.

Because of long COVID, I think it's fair to say researchers are putting more time and energy and resources behind understanding these mysterious illnesses, because so many people have long COVID.

So what is the latest researchers have discovered about possible causes of long COVID that might have impact on other chronic diseases?

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