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dCT imaging of patients with post-acute sequelae of COVID-19 (PASC), more commonly known as long COVID, revealed that small airways disease persisted months after infection, a prospective single-center study showed.

In chest CT scans of approximately 100 long COVID patients -- a third of whom had been hospitalized following their initial infection -- air trapping was observed in 58% and ground glass opacities were found in 51% of patients' lungs, according to Alejandro Comellas, MD, of the University of Iowa in Iowa City, and colleagues.

"[Ground glass opacities], which are frequently observed during acute COVID-19 and often in an organizing pneumonia pattern," were significantly more prevalent in patients who had severe cases, affecting 94% of those admitted to the intensive care unit (ICU) compared to 36% of those who did not require hospitalization (ambulatory group), Comellas and colleagues wrote in .

"For the first time, we're describing small airways disease in this population of COVID-19 patients with persistent symptoms," Comellas said in a press release. "Something is going on in the distal airways related to either inflammation or fibrosis that is giving us a signal of air trapping."

CT scans were taken at a median 75 days following the patients' initial diagnosis, and approximately half the participants with air trapping also had ground glass opacity. This is the latest in a growing number of conditions that are being associated with long COVID. Others include "brain fog," .

Most notably, Comellas and colleagues found that the mean percentage of total lung classified as ground glass opacities was 28.7% in the ICU group and 13.2% in patients hospitalized without needing ICU care (hospitalized group), both significantly higher than the 3.7% observed in the ambulatory group, which was in turn significantly higher than healthy controls (0.06%, P<0.001 for both).

Spirometry and lung volumes in ambulatory participants were not different compared with healthy controls, but the percentage of lung affected by ground glass opacity in these milder cases suggests "ongoing lung inflammation, edema, or fibrosis," the team wrote.

The mean percentage of total lung affected by air trapping was 27.3% in the ICU group, 34.6% in the hospitalized group, 25.4% in the ambulatory group, and 7.2% among healthy controls

"We did not observe airflow obstruction by spirometry in any group, suggesting that air trapping in our cohort is due to involvement of small rather than large airways," Comellas and colleagues wrote. "Small airways are not readily identified by lung imaging, but have established the presence of air trapping on chest CT as a marker of functional small airways disease (fSAD)."

"Taken together, our findings suggest that SARS-CoV-2 infection itself leads to fSAD and air trapping," the investigators wrote.

Writing in an , Brett Elicker, MD, of the University of California San Francisco, said: "When considering the long-term pulmonary effects of COVID-19 infection, this is an important finding and may correspond to the development of post-viral constrictive bronchiolitis, an entity seen with other viral infections and in particular, adenovirus infection."

Comellas and co-authors suggested that a potential mechanism may be related to ACE2 receptors, which are expressed throughout the lungs and in small airways.

In addition, the study found that the median percent pre-bronchodilator forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) in the hospitalized groups were significantly lower than the ambulatory group, while no differences were seen between the ambulatory group and healthy controls.

Both Elicker and the study authors noted that it was not clear if these abnormalities in the airways of long COVID patients would be permanent, and that longer-term studies are needed.

The single-center study was conducted in Iowa from June to December 2020 and included 100 patients who were symptomatic more than 30 days after their COVID-19 infection; 106 healthy controls were included from a separate study conducted in 2018.

For the PASC group, 67 were treated in an ambulatory care setting during the acute infection period (21 days after diagnosis), 17 were hospitalized without needing ICU care, and 16 were hospitalized and required ICU care.

The median age of this group was 48 years, though those hospitalized with and without the ICU were older than those who only required ambulatory care (60, 64, and 44 years of age, respectively). Overall, 66% were women, 85% were white, 10% were Latino, and 5% were Black.

A total of 76 had a coexisting condition: 59 were obese, 27 had hypertension, and 26 had asthma. Three-quarters were never-smokers, though in the hospitalized group 53% were smokers.

Comellas and colleagues said a limitation to the study was that it included only participants who were infected early in the pandemic, so that more recent variants, such as Delta and Omicron, were not represented.

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