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Federally funded scientists have proposed a definition of long-Covid based on symptoms identified in a large study published Thursday in the Journal of the American Medical Association.
The definition is based on 12 symptoms that most differentiate people with long Covid six months or more after they were infected from people who did not have the coronavirus.
Since the beginning of the pandemic, many people have suffered from a myriad of symptoms, some of them debilitating, that persist long after they have been infected with Covid-19.
Patients have adopted the name Long Covid. Scientists call the condition post-acute episodes, or PASC.
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However, there is still no systematic, widely accepted definition of long-Covid for research that could serve as a basis for future tools to diagnose the condition.
“It’s really about finding a concrete, reproducible specific definition for Long Covid,” said Dr. Leora Horwitz, study author and professor at NYU Grossman School of Medicine.
The study, funded by the National Institutes of Health, looked at nearly 10,000 participants at 85 hospitals, health centers and community centers in 33 states.
More than 8,600 patients who had Covid were compared to more than 1,100 patients who did not have the virus.
The research is part of the NIH’s extensive $1.15 billion RECOVER research initiative, which aims to define Long Covid, understand the causes of the condition, and develop treatments for it. RECOVER is an acronym for Researching COVID to Enhance Recovery.
Symptoms most noticeable in long-Covid participants included loss of smell and taste, discomfort after exertion, chronic cough, brain fog, thirst, palpitations, chest pain, fatigue, changes in sexual desire, dizziness, gastrointestinal issues and abnormal movements and hair loss.
The scientists awarded points based on how much each symptom distinguished participants with long Covid from those who had not contracted the virus.
A participant who scores 12 or more points is considered to have probably had long-term illness with Covid.
For example, loss of smell and taste and discomfort after exertion were more noticeable than other symptoms and were rated 8 and 7 points, respectively. Palpitations and dizziness, which are characteristic of long covid but also common in many other diseases, were given 2 and 1 points, respectively.
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Future clinical use
Horwitz, author of the study, said the proposed definition of Long Covid could help develop a way for doctors to diagnose patients.
However, Horwitz said that the definition presented in the study is an early working definition that still needs to be refined and is not yet ready for clinical use.
In the absence of a universally accepted definition, many patients with long-term illness from Covid-19 face difficulties in obtaining appropriate medical care, especially in the early stages of the pandemic, as some symptoms can also occur with other conditions and make a diagnosis difficult.
There are no tests that can diagnose Long-Covid using markers in the blood. Scientists participating in RECOVER are trying to understand the underlying biology causing Long Covid, which could potentially lead to such testing in the future.
Horwitz said the proposed definition could help create a rubric to diagnose long-Covid patients in a similar way to lupus. There is no single blood test that can diagnose lupus, so doctors also rely on a collection of common symptoms to determine if a patient has the disease.
Horwitz said the goal is to give researchers a more systematic definition that could be used to answer questions about risk factors and the likelihood of how long Covid lasts after repeat infection, among other things, and between different variants of the virus.
Biological samples from patients who developed Long Covid during the study could be used to study the causes of the condition and potentially help identify treatments and guide enrollment in future clinical trials, the study said.
Long Covid more common before Omicron
The study also found that long-Covid was more common among infected people before the Omicron variant swept the US in December 2021.
About 17% of patients admitted during Omicron therapy more than 30 days after their infection developed Long-Covid. In contrast, about 35% of those infected before the omicron era developed long-Covid.
But patients who became reinfected during the Omicron phase were more likely to develop long Covid than those who reported infection when the variant was on the rise. About 21% of those with repeat infections who enrolled after 30 days developed long-term Covid illness, compared to 16% who developed Covid once.
People who were fully vaccinated had a lower risk of contracting Long-Covid regardless of when they were infected.
Approximately 16% of vaccinated participants who became infected while on Omicron therapy developed Long-Covid, compared to 22% who did not receive their immunizations. Before Omicron, 31% of people who had been infected and were aware of their vaccinations contracted Long-Covid, compared to 37% who were unvaccinated.