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Pediatric bronchiolitis hospitalizations took a brief downturn during the pandemic before consistently rising thereafter, with seasonal patterns yet to return to normal, a nationwide study found.

After admissions plummeted by 69.2% in the 2020-2021 season, the subsequent 2022-2023 season tracked at 75.3% above the pre-pandemic median. Patients who were ages 12 to 23 months saw the largest uptick in bronchiolitis admissions, increasing 2.2 times in 2022-2023 when compared to the pre-pandemic seasons, reported Jonathan Pelletier, MD, of Akron Children's Hospital, Ohio, and co-authors.

Researchers pointed to public health measures taken during the COVID-19 pandemic that may have also affected immunity in this patient population.

"This study supports prior work suggesting that transient social distancing may result in waning population immunity, and these findings highlight the importance of sustained interventions, such as respiratory viral vaccines and monoclonal antibodies, to help reduce the burden of illness," Pelletier's group wrote in the cross-sectional study, published in .

The study found that the seasonality of bronchiolitis infections also shifted, peaking in August 2021 and November 2022 as opposed to typical December through February peaks seen before the pandemic.

Hossein Sadeghi, MD, of Columbia University Irving Medical Center in New York City, noted that the study directly echoed his own experiences.

"We realized that in the last couple of years that we had bronchiolitis during the off-winter season, so we had bronchiolitis during summertime, which was unusual in the northeast, especially with RSV [respiratory syncytial virus] infections. But, that eventually may regress to the typical pre-pandemic [timing] as the population immunity returns to the historical norms," he told 乌鸦传媒.

He explained that pandemic restrictions and interventions may have led to decreased exposure to conditions that can cause bronchiolitis, ultimately resulting in waning immunity. As those interventions have pulled back and travel has increased, transmission of infections is increasing as well.

Bronchiolitis remains one of the most common causes of infant hospitalization.

Sadeghi stressed the importance of precautions among caregivers and providers -- ranging from masking to ensuring quality sleep and nutrition -- to help prevent infections as rates continue to make their way back to pre-pandemic patterns.

"We need to do whatever is important to have interventions that would reduce the rate of infection. So, if we can do infection control with hand hygiene, we should emphasize that. If there are vaccinations that for some of these viruses such as RSV, that's new, monoclonal antibodies, or flu vaccine, that we can use, we should emphasize that, so that we can control the rate of those infections," he said. "And by doing that, then they'll have less severe infection, less hospitalizations, and less ICU admissions."

The study included 400,801 bronchiolitis admissions for 349,609 children from July 2010 to June 2023. Data were taken from hospitals within the Pediatric Health Information System (PHIS). All admissions for patients under age 2 were included in the analysis, and hospitals within the system were only excluded if they did not have data for every bronchiolitis season in the study period.

The median patient age was 6 months, and the patient population was 41.3% girls. Of those patients, 43.7% were white, 24.7% were Hispanic, and 19.3% were Black.

Prior to the pandemic, between both the 2010-2011 and 2019-2020 seasons, median annual admissions for bronchiolitis had reached 29,309. In 2020, 9,030 bronchiolitis admissions were reported, which was significantly lower than the predicted 35,418. The next year however, admissions increased, with 5,036 admissions in August 2021 alone instead of the predicted 243.

Of the 41 hospitals included in the analysis, 39 hospitals received more admissions during the course of the 2022-2023 season than they had, on average, prior to the pandemic.

Study authors also found that the severity of bronchiolitis apparently changed during COVID-19, despite the lack of a validated severity of illness score for infants with bronchiolitis outside of the intensive care unit (ICU).

From 2010 to 2019, prior to the pandemic, there had been a decrease in the amount of patients sent to the pediatric ward (down from 81.2% to 59.1%) while there was an increase in patients sent to the ICU without either noninvasive ventilation or invasive mechanical ventilation (5.9% to 6.3%).

However, these trends reversed during the pandemic era, when more children were admitted to the pediatric ward (going up to 65.2% in 2022) and less so to the ICU.

Chief among limitations to the study was its reliance on a non-comprehensive database of pediatric admissions. The PHIS was unable to track patient relocation or provide granular vital sign information, which hindered severity scoring for bronchiolitis and left open the possibility that changes in admission and ventilation rates represent changes in clinician practice, not patient acuity.

Furthermore, bronchiolitis admissions were identified by ICD-9 and ICD-10 code, which may underestimate true admission numbers.

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