CHICAGO — A long-time study is revealing new information about the ailments that plague a third of COVID survivors.

The findings on long COVID are very different depending on whether patients were hospitalized or recovered at home.

Dr. Igor Koralnik, a neurologist with Northwestern Medicine, said nearly 2,000 patients from 31 states have traveled to the clinic in search of answers.

“Patients complain of brain fog, headache, muscle pain, trouble with smell and taste, numbness tingling, blurry vision and ringing in ears,” Koralnik said.

In the 100 study, patients who were hospitalized and placed on ventilators, many with co-morbidities such as hypertension, diabetes and obesity prior to a COVID infection, the researchers noted broader, more serve lasting neurological symptoms.

“When people are older, had other diseases before COVID, seriously affected by COVID-19, pneumonia, maybe go to the ICU, had all kinds of complications that may cause brain damage,” Koralnik said.

That doesn’t appear to be the case among the non-hospitalized study group, generally, a younger population who had milder infections.

“The previously hospitalized group were abnormal in their processing speed, attention and memory, whereas those non-hospitalized patients had problems only on attention tasks,” Koralnik said.

Koralnik said the non-hospitalized patients with long-COVID may have experienced an autoimmune response, not brain damage.

“Which has been triggered by the virus confusing the immune system that there is something abnormal in the body that needs to be attacked or persistent infection in gut or nasopharynx,” Koralnik said.

The researchers hope the new information will help guide treatments for both patient groups.

“Those patients need to be analyzed differently, separately and also treated with targeted intervention based on their exact problem,” Koralnik said.

Northwestern Medicine offers a support group for survivors and a comprehensive COVID clinic.