Some people may experience "long colds," or long-term symptoms following common colds, flu, pneumonia or other respiratory illnesses, similar to the pattern seen in long COVID, according to a new study from Queen Mary University of London.

Published in The Lancet's EClinicalMedicine journal Friday, researchers found that even people with acute respiratory infections who tested negative for COVID-19 could still experience long-term symptoms at least 4 weeks after infection, including coughing, stomach pain and diarrhea. Those with long COVID were more likely to report ongoing problems with sense of taste or smell, lightheadedness or dizziness.

While researchers did not measure duration differences between the "long cold" and long COVID symptoms, they did find people in both groups were more likely to report more severe symptoms if they had been previously infected.

The study was part of COVIDENCE UK, the university's national study of COVID-19, which was launched back in 2020. For this research, they analyzed questionnaire data from 10,171 U.K. adults between January and February 2021, looking for 16 symptoms commonly associated with long COVID: coughing, sleep problems, memory problems, difficulty concentrating, muscle or joint pain, problems with sense of taste or smell, diarrhea, stomach pain, changes to voice, hair loss, unusual racing of the heart, lightheadedness or dizziness, unusual sweating, breathlessness, anxiety or depression, and fatigue.

While long-lasting symptoms, also known as post-acute infection syndromes, are "not a new phenomenon," the authors write, they often go undiagnosed due to a wide range of symptoms and lack of testing.

"Our findings may chime with the experience of people who have struggled with prolonged symptoms after having a respiratory infection despite testing negative for COVID-19 on a nose or throat swab," said Professor Adrian Martineau, chief investigator of COVIDENCE UK and clinical professor of respiratory infection and immunity at Queen Mary University of London, in a news release.

Martineau noted ongoing research into the long-term effects of COVID-19 and other infections is important to help understand why some people experience more prolonged symptoms than others.

"Ultimately this could help us to identify the most appropriate form of treatment and care for affected people," he said.

Millions of Americans report having long COVID — an array of symptoms, which can be debilitating, that may linger for months or years after a COVID infection — according to recent data from the Centers for Disease Control and Prevention's National Center for Health Statistics.

In reports published last month, using data from 2022 National Health Interview Survey, the agency said 6.9% of U.S. adults reported ever having long COVID, while 3.4% said they currently had the condition at the time of the survey. Based on U.S. Census data, that would mean nearly 18 million have suffered from the condition at some point since the pandemic began, and almost 9 million did at the time of the survey.

The survey data also found women were more likely than men to report long COVID. 

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• COVID-19