Updated at 7:50 p.m. May 25

A national study of almost 10,000 people has identified 12 key symptoms of long COVID. The study is a starting point to diagnosing the disease, which can include a range of sometimes debilitating symptoms.

People who suffer from long COVID experience symptoms more than 30 days after being infected with the coronavirus. The study found the most common of those long COVID symptoms are a loss of smell or taste, chronic cough, and a worsening of symptoms after minor physical or mental exertion. Other common symptoms were brain fog, thirst, palpitations, chest pain, fatigue, a change in sexual desire or capacity, dizziness, gastrointestinal symptoms, and abnormal body movements.

Researchers at Mass General Brigham hospital system led the study of long COVID as part of a nationwide effort to learn more about the disease. Long COVID is estimated to have affected as many as 100 million people worldwide, and hundreds of thousands of Massachusetts residents.

“There were really two pieces to the findings,” said Andrea Foulkes, chief of biostatistics at Massachusetts General Hospital, and a co-author of the study. “The first was to identify people who were likely to have long COVID. And then within that group we were able to identify people who had various manifestations of long COVID. And it does appear as though there are different manifestations for different people.”

The study sorted through 44 potential symptoms and asked thousands of people across 85 sites nationwide what they were experiencing six months after being infected with the coronavirus — the researchers then whittled down those dozens of symptoms to 12, and gave a proposed weight to each one indicating how likely it was to indicate long COVID as opposed to other illnesses.

For instance, loss of smell or taste, or worsening symptoms after exertion would bring a person around two-thirds of the way toward qualifying for a long COVID diagnosis. A chronic cough, brain fog and thirst would bring someone a quarter to a third of the way.

Foulkes emphasized that the listing and weighting of 12 symptoms are early findings, and that, while it can indicate who is very likely to have long COVID, there may be people who have long COVID who would not be diagnosed as such under their system, and that clinical lab tests need to be developed as well. And she underscored that the disease manifests differently for different people.

“So by understanding these different manifestations,” said Foulkes, “we can begin that process of looking under the hood, looking further at the data that we have available . . . to understand better what is the cause of these different symptoms. Importantly, once we understand [the] underpinnings of [the] disease, then we can begin thinking about the best way to treat patients.”

Foulkes added, “we have found in our research that higher scores are associated with poorer overall physical health and quality of life. So we know that we do need to continue looking at the meaning behind these scores.”

People who have not been vaccinated against the coronavirus, as well as those who have been infected multiple times, appear to be at higher risk of developing long COVID or getting a more severe case of the syndrome, researchers stated. Future research will more closely examine risk factors.

Correction: This story has been updated to correct Andrea Foulkes' title.