Pandemic-Era Bronchiolitis Admissions Found Not to Have Decreased to Pre-Pandemic Levels


This new data suggests that hospital facilities in the US may need to plan for potentially atypical timing of bronchiolitis season once more for 2023.

Kailey A. Remien, DO

Credit: X (Twitter)

Kailey A. Remien, DO

Credit: X (Twitter)

The seasonality of bronchiolitis has not returned to the patterns of the pre-COVID-19 pandemic era (2010-2019), according to new findings, suggesting the need for hospital facilities to plan for potentially-atypical timing this year.1

The investigators that identified these findings noted that bronchiolitis cases usually follow a seasonal pattern that is predominant in winter, with its peak occurring from December - February within the Northern Hemisphere and May - July within the Southern Hemisphere. The measures such as social distancing and masks were linked with significant reductions in bronchiolitis admissions in the early period of the pandemic.2

To assess changes since the pandemic ended, this new research was led by Kailey A. Remien, DO, from the Department of Medical Education at Akron Children’s Hospital in Ohio. Remien and colleagues worked to assess the changes in COVID-19 pandemic era bronchiolitis admissions, comparing them to those of the pre-pandemic period from 2010 - 2019.

“We hypothesized that admissions would be higher than expected, that there would be unusual seasonality, and that patients would be older than those in previous years due to waning herd immunity from lack of exposure,” Remien and colleagues wrote.

Background and Findings

The investigators used a retrospective cross-sectional study design, extracting their data from the Pediatric Health Information System database. This database covers 41 children's hospitals across the US.

The research team noted that bronchiolitis shows its seasonality pattern predominantly during the winter months, so their hospitalization data was categorized based upon bronchiolitis seasons spanning from July - June. The team included all pediatric patients as subjects who had been both under 2 years of age and admitted with a bronchiolitis diagnosis within the timeframe of July 2010 - June 2023.

The investigators stratified the bronchiolitis seasons between 2010 - 2011 and 2019 - 2020, with these being labeled as the pre-pandemic period and the seasons from 2020-2021 through to 2022-2023 being the pandemic period.

The research team carried out their analysis of the data from July 2010 - June 2023, with their main focus of the research being to look at the variation in hospitalization numbers for cases of bronchiolitis over different seasons and months.

The team transformed their historical monthly admission data from the pre-pandemic era into time series to achieve their primary goal, and these elements were utilized to formulate forecasting models to help predict monthly admissions in the pandemic period.

Overall, the investigators looked over a total of 400,801 admissions for bronchiolitis, and this was from 349,609 subjects. They found that their study population had a median age of 6 months (interquartile range of 2 to 12 months), and it was made up of 58.7% male subjects and 43.7% White.

They found that hospitalizations had a steady increase during the pre-pandemic time period, noting a median of 29,309. Despite this increase, the research team identified a major 69.2% reduction in the 2020 - 2021 season, followed by a 75.3% increase in the 2022 - 2023 season.

The investigators also reported that the subjects who had been admitted in the pandemic period were shown to have been somewhat older versus the subjects seen in the pre-pandemic period, with a median age of 7 months as opposed to 6 months. This was noted to be a statistically significant difference (P < .001).

They also found an increase in the admissions to intensive care units (ICU), identifying an increase from 32.2% in the pre-pandemic time period to 36.7% in the pandemic period (P < .001). The investigators noted that the seasonality of admissions due to bronchiolitis showed shifts in the pandemic period, demonstrating that peak admissions were found to have happened in August 2021 and November 2022.

The research team found that these occurrences were consistent in their sensitivity analyses that had excluded young patients with complex chronic conditions and with repeat admissions. In an additional sensitivity analysis covering all viral lower respiratory tract infections in those younger than 5 years, the team found 66,767 admissions were shown in the 2022 - 2023 period as opposed to 35,623 in the pre-pandemic period.

Overall, the team found the most substantial increase in the subjects who were aged 24 to 59 months. While their findings were informative, the team acknowledged some of the potential limitations of their research.

“Because the PHIS is not geographically comprehensive, patient relocation or changes in referral patterns during the study may affect the results,” they wrote. “For example, if community hospitals increased the proportion of children referred to children’s hospitals during the COVID-19 pandemic, it would increase the number of admissions captured in the PHIS.”


  1. Remien KA, Amarin JZ, Horvat CM, et al. Admissions for Bronchiolitis at Children’s Hospitals Before and During the COVID-19 Pandemic. JAMA Netw Open. 2023;6(10):e2339884. doi:10.1001/jamanetworkopen.2023.39884.
  2. Pelletier JH, Rakkar J, Au AK, Fuhrman D, Clark RSB, Horvat CM. Trends in US pediatric hospital admissions in 2020 compared with the decade before the COVID-19 pandemic. JAMA Netw Open. 2021;4(2):e2037227. doi:10.1001/jamanetworkopen.2020.37227.
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