Bronchiolitis

Alex Koo, MD

Bronchiolitis season is here, running from October to March timeframe.  It accounts for 2.1 million outpatient visits and almost 20% of all pediatric hospitalizations annually in the US.  There has also been a 75% increase in hospitalizations from the 2022-2023 season, compared to 2010-2019 seasons.¹  

Affecting children under age 2, viruses affect the terminal bronchioles, leading to excessive mucus production, sloughing, and ultimately small airway obstruction.  Given the smaller diameters of airways in infants along with obligate nasal breathing, this can lead to significant areas of atelectasis, V/Q mismatch, and nasal obstruction, respectively.   Ultimately, this leads to hypoxia, increased work of breathing, and poor feeding.  Respiratory syncytial virus (RSV) accounts for 60-80% of the all cases of bronchiolitis.²

Symptoms

Children may present with fever, cough, rhinorrhea, and wheezing.  Testing is not necessary, and bronchiolitis is largely clinical diagnosis based on the patient age, presentation, exposures, and risk factors.  However, nasal swab testing for RSV (i.e. immunoenzymatic assay IgM), influenza, COVID-19, and other respiratory panels may show a viral etiology.  A chest x-ray will demonstrate peribronchial and perihilar thickening, typical of a viral process, but can be used to evaluate for a superimposed bacterial infection. 

The reference slide above is taken from our Emergency Medicine and Urgent Care Professional Development Series

Treatment of Bronchiolitis

Outpatient treatment hinges on supportive care and observing for worsening clinical status requiring hospitalization, oxygen therapy, and hydration.  Humidifiers, frequent nasal suctioning with saline mist prior to feeds and naps, along with ensuring adequate fluid intake is the mainstay.  

If respiratory support and hospitalization is needed to maintain oxygenation and improve work of breathing, high flow nasal cannula (HFNC) provides humidified, warmed oxygen and some positive pressure to open up areas of atelectasis.  A typical starting setting of HFNC is about 1 L/kg and 30-40 FiO2, but may be adjusted based on hospital protocols and preferences.  

Prevention:

In 2023, the FDA approved the intramuscular injection monoclonal antibody, nirsevimab-alip (Trade Name: Beyfortus) for use in decreasing the incidence of hospitalizations from bronchiolitis.  After safety trials, there were two randomized, double-blind, placebo-controlled, multicenter clinical trials demonstrating a 70-75% decrease in hospitalizations from bronchiolitis in term and preterm infants receiving the antibody, compared to those receiving placebo.  Below is a summary recommendation from the CDC.^3,4

Nirsevimab Monoclonal Antibody

Nirsevimab treatment consists of a 1 time intramuscular injection that lasts approximately 5 months. The most common side effects are rash (0.9%) and pain at the injection site (0.3%).  There have been reported anaphylaxis reactions, but these are rare. This medication can be given with other vaccinations. The CDC recommends receiving nirsevimab October-late March in the following groups:

1) For Infants under 8 months if:

-The mother did not receive RSV vaccine (i.e. Pfizer’s Abrysvo) during pregnancy, or

-The mother’s RSV vaccination status is unknown, or

-The infant was born within 14 days of maternal RSV vaccination.

2) For Infants 8-19 months if:

-Children with chronic lung disease of prematurity who required medical support (chronic corticosteroid therapy, diuretic therapy, or supplemental oxygen) any time during the 6-month period before the start of the second RSV season

-Children with severe immunocompromise

-Children with cystic fibrosis who have either 1) manifestations of severe lung disease (previous hospitalization for pulmonary exacerbation in the first year of life or abnormalities on chest imaging that persist when stable), or 2) weight-for-length <10th percentile

-American Indian or Alaska Native children

Severity and Disposition

Consideration of inpatient versus outpatient treatment can be determined by the severity of patient illness. The chart below serves as a good reference to determine illness severity.

Severity Interpretation: Mild (1 to 4), Moderate (5 to 8), Severe (9 to 12)

The most serious timeframe of bronchiolitis will peak by days 3-5 of infection before slowly improving and the focus of the clinician is to ensure 1) adequate respiratory status and 2) feeding.  The Respiratory Severity Score (RSS) – while somewhat subjective – can provide a numerical scoring to evaluate their overall respiratory status (Table 1).  Children in the “moderate” and “severe” categories may need oxygen therapy and hospitalization.  

Summary

The timing, seasonality, and predictability of bronchiolitis make it a no-miss diagnosis in your differential diagnosis. Understanding the symptoms, recognizing the diagnosis, and providing the correct treatment is critical.

References

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. Dalziel SR, Haskell L, O’Brien S, Borland ML, Plint AC, Babl FE, Oakley E. Bronchiolitis. Lancet. 2022 Jul 30;400(10349):392-406. doi: 10.1016/S0140-6736(22)01016-9. Epub 2022 Jul 1. PMID: 35785792.
3. Commissioner, Office of the. “FDA Approves New Drug to Prevent RSV in Babies and Toddlers.” FDA, 18 July 2023, www.fda.gov/news-events/press-announcements/fda-approves-new-drug-prevent-rsv-babies-and-toddlers.
4. “Healthcare Providers: RSV Immunization for Infants and Young Children | CDC.” Cdc.gov, 25 Oct. 2024, www.cdc.gov/vaccines/vpd/rsv/hcp/child.html#resources. Accessed 19 Nov. 2024.

Here are a couple helpful Links for treatment options:

Options for RSV Infant Prevention At-A-Glance

Package Insert for Nirsevimab

Alex Koo

Alex Koo, MD is a board-certified emergency medicine physician with a passion for medical education. He received his undergraduate degree at the University of Virginia, medical degree from Jefferson Medical College, and emergency medicine residency training at Madigan Army Medical Center. During his time in residency, he was nominated and selected as the ‘Resident of the Year’ from the Emergency Medicine Residents’ Association. Dr. Koo is an Associate Professor of Clinical Emergency Medicine at The Georgetown School of Medicine in Washington, DC and Adjunct Assistant Professor of Military and Emergency Medicine at The Uniformed Services University of the Health Sciences in Bethesda, MD. Currently, he serves on the residency leadership and simulation team for the Georgetown/Washington Hospital Center Emergency Medicine Residency, providing simulation, didactic, and clinical bedside teaching to Georgetown and USUHS medical students, PAs, and residents. He practices emergency medicine as an award-winning attending/faculty in both tertiary academic institutions and EM physician in small community emergency departments. Dr. Koo is a decorated Army veteran, having served in conventional and unconventional units in a variety of settings from deployed, austere environments to academic emergency departments to primary care clinics. He worked alongside some amazing APPs and continues to do so in the community emergency department setting.