Bronchiolitis is a lower respiratory tract infection (LRTI) characterized by inflammation of the bronchioles in children < 2 years of age. Respiratory syncytial virus (RSV) is the primary pathogen, although many viruses have been implicated in bronchiolitis. Patients first present with upper respiratory tract infection (URTI) symptoms (e.g., low-grade fever, nasal congestion) followed by a cough, wheezing, and, in severe cases, . Bronchiolitis is a clinical diagnosis; diagnostic studies are usually not needed unless the child presents with severe illness that requires an evaluation for associated complications (e.g., superinfection, respiratory acidosis) or if the diagnosis is uncertain. Management consists of supportive treatment (e.g., nasal suction) and close monitoring. Severe illness requires hospitalization for additional management (e.g., IV fluids, respiratory support, nutritional support) and close monitoring of respiratory status. Bronchiolitis prevention includes RSV vaccination of pregnant individuals in the third trimester and routine passive immunization of all infants < 8 months of age with RSV monoclonal antibodies.
- Primarily affects children < 2 years of age
- Peak incidence: 2–6 months of age
- Common during winter months
Epidemiological data refers to the US, unless otherwise specified.
- Most common: respiratory syncytial virus (RSV), a paramyxovirus
- Less common
- Risk factors for severe bronchiolitis 
- Initially, URTI symptoms (e.g., copious rhinorrhea, low-grade fever, cough) 
- Followed by LRTI symptoms 
- Crackles, wheezes; , and/or rhonchi on auscultation 
- Findings vary minute-to-minute as mucus is cleared and/or respiratory efforts change.
- Severe illness: respiratory distress (usually occurs in children < 1 year of age)
- Often associated with poor feeding 
If significant nasal congestion is present, provide nasal suction and reassess respiratory status to differentiate upper airway involvement (clear breath sounds after nasal suction) from lower airway involvement (abnormal breath sounds after nasal suction). 
Symptoms typically peak 3–5 days after onset and then gradually improve over 2–3 weeks. The onset of new symptoms or worsening of existing symptoms (e.g., fever) after 3–5 days should raise concern for . 
General principles 
- Bronchiolitis is a clinical diagnosis based on the patient's age (< 2 years) and the presence of classic .
Further testing is not usually required but may be considered in patients with:
- Severe disease, e.g., if there is concern for respiratory failure
- Diagnostic uncertainty to rule out
Laboratory studies 
- Blood gas 
- Respiratory viral panel
- Studies to exclude differential diagnoses (not routinely recommended)
- Indications: severe disease if there is diagnostic uncertainty or suspected complications (e.g., pneumothorax, pneumonia)
- Potential findings
- Determine the need for immediate respiratory support.
- Start supportive measures including adequate hydration, relief of nasal congestion and/or obstruction, and monitoring.
- Screen for and initiate if present.
- Provide with close medical follow-up for patients who do not meet the admission criteria.
Admission criteria for bronchiolitis 
- Unwell appearance, lethargy
- Moderate to severe (including significantly elevated respiratory rate for age)
- Ongoing respiratory support required
- Need for supplemental hydration
- History of apnea
- Consider if:
- Risk factors for severe bronchiolitis are present
- Supportive care at home is not feasible 
Inpatient management of bronchiolitis 
- Frequently monitor routine vital signs including O2 saturation; consider using:
- Continuous pulse oximetry 
- An objective respiratory score 
- Adjust as needed.
- Provide regular external nasal suction. 
- Consider scheduled nebulizations with 3% hypertonic saline 
Caloric and fluid support
- Ensure patients receive the recommended daily intake for their age.
- Encourage normal oral feeds (e.g., with breastmilk, formula, regular diet for age) as tolerated.
- Consider NG/IV fluids for any of the following: 
Respiratory distress increases caloric and fluid requirements but also increases the risk for aspiration during oral feeds. Nutritional and fluid support via a feeding tube (orogastric or nasogastric) and/or intravenously is often necessary. 
- Start RSV).  in accordance with local protocols (e.g., for
- If used, discontinue palivizumab prophylaxis. 
Outpatient management of bronchiolitis 
- Arrange follow-up within 24 hours. 
- Educate caregivers on:
- Signs of deterioration and the need to seek immediate medical attention if present 
- How and when to provide nasal suction
- The expected course of disease
- Encourage adequate oral caloric and fluid intake.
- Advise caregivers to avoid exposing the patient to second-hand smoke; offer for household members.
Advise caregivers to seek immediate medical attention if the child shows signs of deterioration such as dehydration, poor feeding, lethargy or irritation, new fever, and/or signs of respiratory distress. 
- No URTI symptoms
- Asymmetric crackles: bacterial or viral pneumonia
- Neonatal fever: neonatal sepsis
The differential diagnoses listed here are not exhaustive.
General measures 
- Vaccinate pregnant individuals against RSV at 32–36 weeks' gestation. 
- Encourage exclusive breastfeeding for the first 6 months of life.
- Educate caregivers on and .
- Advise avoiding large crowds.
- Inform caregivers about the increased risk of infection at daycare.
- Offer advice on tobacco smoke exposure. to any individuals who smoke in the household to reduce
Administration of infants.  to pregnant individuals minimizes the risk of bronchiolitis in
RSV prophylaxis 
- Monoclonal antibodies that target the RSV fusion (F) protein are used to provide passive immunization.
- RSV prophylaxis reduces RSV-related hospitalizations (e.g., due to bronchiolitis, pneumonia) in infants.
- Two RSV monoclonal antibodies are now available.
- Nirsevimab (preferred)
- Palivizumab (alternative) 
|Indications for RSV prophylaxis and approved agents |
|Indications||Agent and administration|
|Routine prophylaxis in 1st RSV season|| |
Indications for additional RSV prophylaxis in 2nd RSV season
|Infants < 12 months of age|| |
|Children 12–24 months of age|