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Researchers say long-term symptoms from non-COVID respiratory illnesses need to be addressed./Getty Images
  • Researchers say there may be lasting health impacts from non-COVID acute respiratory illnesses that are going unrecognized.
  • Those who have an acute respiratory illness but test negative for COVID-19 may experience a similar burden of lingering symptoms as those with long COVID.
  • Both long COVID and lingering symptoms from other acute respiratory illnesses decrease health-related quality of life
  • Experts say better definitions are needed to make diagnosis of lingering conditions easier.

As studies into long COVID continue, researchers have identified that long-term symptoms from other acute respiratory infections may be going unnoticed.

Research published October 6 in The Lancet’s EClinicalMedicine reports that people who experience an acute respiratory infection but test negative for COVID-19 may also experience “long colds” and a similar burden of symptoms as those experiencing long COVID.

Adrian Martineau, PhD, chief investigator of COVIDENCE UK and clinical professor of respiratory infection and immunity at Queen Mary University of London, said in a press statement:

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.

Ongoing research into the long-term effects of COVID-19 and other acute respiratory infections is important because it can help us to get to the root of 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.”

For the study, researchers compared the severity and prevalence of long-term symptoms following COVID-19 and other acute respiratory infections in which the person tested negative for the novel coronavirus.

Data was collected from COVIDENCE UK, a large-scale study that began in 2020 with more than 19,000 participants. In this study, the researchers examined data from more than 10,000 adults.

Of the people studied, 1,311 had COVID-19, and 472 had a non-COVID acute respiratory infection.

The researchers reported that both types of illness were associated with a range of long-term symptoms and decreased health-related quality of life.

Those with symptoms following COVID-19 had greater odds of problems with taste and smell as well as light headedness and dizziness.

Those experiencing lingering symptoms following a non-COVID acute respiratory infection experienced various symptoms, including:

Severity of symptoms following both COVID-19 and non-covid acute respiratory illnesses were found to be associated with severity of the initial infection.

Those who experienced increased symptom severity were more likely to be female, a frontline worker, overweight, socioeconomically disadvantaged, or have co-morbidities.

The researchers argue that the new focus on long COVID raises the question of whether there are people living with post illness symptoms due to other acute respiratory infections who are being missed.

“Post-acute infection syndromes are not a new phenomenon; indeed, many cases of chronic fatigue syndrome are reported to follow an infection-like episode. Nonetheless, these syndromes often go undiagnosed owing to the wide range of symptoms and lack of diagnostic tests,” the authors wrote.

“Our findings suggest that there may be long-lasting health impacts from other respiratory infections that are going unrecognized, although we do not yet have evidence that these symptoms have a similar duration to long COVID,” the researchers added.

Experts say the study is the latest in a growing body of research investigating the long-term impact of post viral symptoms.

We’re learning increasingly that acute viral infections, such as COVID and influenza, and now perhaps other respiratory viruses, can initiate an inflammatory response,” Dr. William Schaffner, an infectious disease expert at Vanderbilt University in Tennessee who was not involved in the study, told Medical News Today:

“Of course, that’s normal to fight off the virus. However, after the acute illness subsides and the person is feeling better, the inflammatory response in at least some people apparently doesn’t get turned off completely, and it continues to smolder in a chronic fashion,” he added.

Dr. Schaffner noted that prolonged inflammatory response may be at least partially responsible for post-influenza health risks such as heart attacks and stroke.

“You have to recognize them as an illness, and providers unfamiliar with them, at least initially, we have to be frank, didn’t listen to their patients carefully enough. Now we’re being better at that, and we are listening to patients, and we can start to define these illnesses. In the last 15 years, this sense of chronic active inflammation has become more of a defined scientific concept that people are starting to do investigations.”
—Dr. William Schaffner, infectious disease expert

The Centers for Disease Control and Prevention (CDC) defines long COVID as “signs, symptoms and conditions that continue or develop” after a COVID-19 illness.

To meet the criteria under the CDC’s definition, symptoms must persist for at least four weeks after the initial illness.

The World Health Organization (WHO) defines long COVID as the continuation or development of new symptoms 3 months after the initial novel coronavirus infection, with these symptoms lasting for at least 2 months with no other explanation.

At least 10% of people who’ve had COVID-19 could develop long COVID. That amounts to at least 67 million people globally.

Determining how many people live with lingering symptoms following non-COVID acute respiratory illness is difficult.

Dr. Dean Blumberg, the chief of pediatric infectious diseases at the University of California Davis who was not involved in the study, told MNT that part of the problem is a lack of clear definition surrounding what constitutes “long cold” symptoms.

“One of the issues that really has not been well done is there is no good definition for this yet. To advance the field, I think a specific case definition needs to be sorted out and agreed upon, and then it’ll be easier to define. And if you can define it better, then obviously, you can start looking more into what’s causing it and how to treat it.”
—Dr. Dean Blumberg, pediatric infectious disease expert

Another problem is, like long COVID, there is no test to diagnose lingering symptoms for other acute respiratory illnesses.

“To diagnose them, there’s no simple tests,” Dr. Blumberg said. “So there’s no simple blood test; the clinical criteria has taken quite a long time. It took years to figure it out for chronic fatigue syndrome, and with long COVID, it just appears now that it’s sort of coalescing into an agreed-upon definition. And that impacts the second question, which is how do you figure out treatment?” he noted.

Long COVID shares many similarities with other post viral conditions such as chronic fatigue syndrome.

Experts say one benefit of an ever-increasing understanding of long COVID is its benefit for people living with other lingering conditions.

“You can get some symptomatic relief. There is some genuine optimism. Many patients, although it takes a while, improve slowly but deliberately over time,” Dr. Schaffner said.