Bronchiolitis: Symptoms, Types, Causes and Treatment

Bronchiolitis is one of the most common respiratory illnesses in infants and young children, causing significant distress for both patients and their families. Characterized by an inflammation of the small airways, bronchiolitis can range from mild cold-like symptoms to severe respiratory distress requiring intensive medical intervention. Understanding the nuances of its symptoms, types, causes, and evidence-based treatments is crucial for parents, caregivers, and clinicians alike. This article provides a comprehensive, up-to-date overview based on the latest research and clinical guidelines.

Symptoms of Bronchiolitis

Bronchiolitis often begins innocently, resembling a common cold, but can quickly progress to more severe respiratory symptoms. Recognizing the signs early is vital for timely care and intervention.

Symptom	Description	Severity Range	Source(s)
Rhinorrhea	Runny nose or nasal congestion	Mild to severe	1 3 16
Cough	Persistent, often worsening	Mild to severe	1 3 16
Wheezing	Whistling sound during breathing	Indicates airway involvement	1 2 3 16
Tachypnea	Rapid breathing	May signal distress	1 3 16
Retractions	Use of chest/neck muscles to breathe	Moderate to severe	1 3 16
Difficulty Feeding	Trouble eating or drinking	Moderate to severe	3 16
Fever	Mild to moderate elevation in temperature	Variable	3 16
Apnea	Brief pauses in breathing, especially in infants	Severe, high risk	16

Table 1: Key Symptoms

Early Symptoms

Bronchiolitis typically starts with upper respiratory symptoms such as a runny nose (rhinorrhea), nasal congestion, and mild cough. These initial signs are easy to mistake for a standard viral cold and often do not cause alarm at first 1 3.

Progression to Lower Respiratory Symptoms

Within a few days, the illness may progress:

• Cough intensifies and can be persistent.
• Wheezing, a high-pitched whistling sound, becomes apparent when the child breathes out, indicating involvement of the small lower airways 1 2 3.
• Tachypnea (rapid breathing) and retractions (the use of accessory muscles, such as chest and neck muscles, to breathe) are markers of increasing respiratory distress 1 3 16.

Feeding Difficulties and Severe Signs

Infants often struggle with feeding due to difficulty coordinating breathing and swallowing, which can lead to dehydration 3 16. Fever is common, but not always present.

In severe cases, apnea (pauses in breathing) can occur, particularly in very young or premature infants, signaling the need for urgent medical attention 16.

Clinical Spectrum

The severity of symptoms varies widely:

• Mild cases can be managed at home.
• Moderate to severe cases may require hospitalization, especially if there is low oxygen saturation, dehydration, or significant respiratory distress 1 16.

Types of Bronchiolitis

Bronchiolitis is not a one-size-fits-all diagnosis. Recent research reveals a spectrum of disease types and clinical profiles, influenced by factors such as viral cause, age, and individual predisposition.

Type/Phenotype	Distinguishing Features	Typical Patient Group	Source(s)
Acute Viral	Sudden onset, usually RSV or rhinovirus	Infants <2 years	1 3 5 6
RSV Bronchiolitis	Severe, mucus plugging, higher asthma risk	Infants (esp. young)	3 6 12 13
Rhinovirus-induced	Atopic tendency, higher asthma risk	Slightly older infants	4 6 9 10
Other Viral Types	Less common, milder presentation	Infants & young children	6
Bronchiolitis Obliterans	Chronic, post-infectious or post-toxic	Older children/adults	5 7 8 11

Table 2: Bronchiolitis Types

Acute Viral Bronchiolitis

The most common and classic type, acute viral bronchiolitis is seen in infants under two, with symptoms arising rapidly following infection with a respiratory virus 1 5. It is characterized by acute inflammation, edema, and necrosis of the cells lining the small airways 14.

RSV Bronchiolitis

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis, responsible for up to 80% of cases 3 12 13. RSV bronchiolitis tends to affect younger infants more severely, with significant mucus production and airway blockage. These children also have a higher risk of developing recurrent wheezing or asthma later in life 3 6.

Rhinovirus-Induced Bronchiolitis

Rhinovirus is the second most common cause. It is often associated with an atopic background (personal or family history of allergies/eczema) and carries an even higher risk of progression to childhood asthma 4 6 9 10. Rhinovirus bronchiolitis may present with more severe symptoms in certain children 9.

Other Viral Types

Other viruses, such as parainfluenza, influenza, adenovirus, and human metapneumovirus, can also cause bronchiolitis, but these cases are generally less frequent and often milder 6.

Chronic and Uncommon Forms

Bronchiolitis Obliterans

A rare, chronic form, bronchiolitis obliterans, can develop following severe viral infections (notably adenovirus), toxic exposure, or as a complication of transplantation. It is marked by permanent scarring and obstruction of the small airways and can present with persistent cough and progressive breathlessness 5 7 8 11.

Heterogeneous Clinical Profiles

Recent clustering studies have identified distinct clinical profiles among hospitalized children, ranging from mild, non-wheezing types to severe, protracted cases with significant respiratory compromise 4. This diversity has important implications for personalized management and prognostication.

Causes of Bronchiolitis

Bronchiolitis is primarily a viral illness, but several factors contribute to its development and severity. Understanding the underlying causes helps clarify why some children become severely ill while others experience only mild symptoms.

Cause	Description/Details	Population Most Affected	Source(s)
RSV	Most common, severe in infants	Infants <1 year	3 12 13
Rhinovirus	2nd most common, severe with atopy	Infants & young children	6 9 10
Other Viruses	Includes parainfluenza, influenza, etc.	Infants & children	6 16
Coinfections	Multiple viruses, increased severity	Hospitalized infants	9 15
Non-infectious	Post-infectious, post-toxic, idiopathic	Older children/adults	5 8 11
Risk Factors	Prematurity, heart/lung disease, etc.	High-risk infants	16 17

Table 3: Causes of Bronchiolitis

Viral Causes

Respiratory Syncytial Virus (RSV)

• RSV accounts for the majority of bronchiolitis cases, especially in infants under 12 months 3 12 13.
• It is highly contagious and spreads through respiratory droplets.
• Seasonal outbreaks—most cases occur in the winter and early spring 3.

Rhinovirus

• The second most frequent cause, rhinovirus is also associated with more severe disease, especially in children with a history of atopy or eczema 6 9.
• Rhinovirus bronchiolitis also carries a higher risk for later development of asthma 6 9 10.

Other Viruses

• Parainfluenza, influenza, adenovirus, and human metapneumovirus are less common but still significant causes 6 16.

Coinfections

• Some children may be infected with more than one virus at a time, which can worsen symptoms and prolong hospitalization 9 15.

Non-Infectious and Chronic Causes

• Bronchiolitis obliterans can develop after severe viral infections (especially adenovirus), exposure to toxins, certain drugs, or as a result of autoimmune processes 5 7 8 11.
• In adults, bronchiolitis is rare and often linked to occupational exposures, smoking, or underlying autoimmune disease 5 11.

Risk Factors for Severe Disease

Certain infants are at higher risk for severe bronchiolitis:

• Premature birth
• Underlying heart or lung conditions
• Immunodeficiency
• Very young age (especially <3 months)
• Exposure to tobacco smoke

These risk factors can predispose children to more severe symptoms and complications 16 17.

Treatment of Bronchiolitis

Treatment for bronchiolitis is largely supportive, focusing on maintaining adequate oxygenation and hydration. Many previously popular interventions have been shown to be ineffective, underscoring the importance of evidence-based management.

Treatment	Approach/Intervention	Evidence/Recommendation	Source(s)
Supportive Care	Oxygen, fluids, minimal handling	Strongly recommended	3 13 16 17
Nasal Suctioning	Clears secretions for comfort	Useful adjunct	16
Oxygen Therapy	For O2 saturation <90–92%	Indicated if hypoxic	3 13 16
Nutrition/Hydration	NG or IV fluids if unable to feed	Essential in severe cases	3 16 17
Bronchodilators	Albuterol, salbutamol	Not routinely recommended	3 13 14 15 16
Corticosteroids	Systemic or inhaled	Not recommended	3 13 14 15 16
Hypertonic Saline	Nebulized 3% saline	Mixed evidence, optional	15 16 17
Antibiotics	Only for confirmed bacterial infection	Not indicated routinely	3 13 14 16
Adrenaline	Inhaled, emergency use only	Limited, situational use	16 17
Palivizumab	RSV prophylaxis for high-risk infants	Preventive, not treatment	3 6 16

Table 4: Treatment Overview

Supportive Care: The Mainstay

• Oxygen therapy is administered when oxygen saturation drops below 90–92%. Maintaining adequate oxygenation is a priority 3 13 16.
• Hydration and nutrition must be ensured. If infants are unable to feed due to respiratory distress, fluids may be given intravenously or via a nasogastric tube 3 16 17.
• Minimal handling is recommended to avoid agitating the infant, which can worsen respiratory distress 17.

Interventions with Limited or No Benefit

• Bronchodilators (such as albuterol/salbutamol) have not shown consistent benefit and are not recommended for routine use 3 13 14 15 16.
• Corticosteroids (systemic or inhaled) do not improve outcomes and are not recommended 3 13 14 15 16.
• Antibiotics are not indicated unless there is clear evidence of secondary bacterial infection 3 13 14 16.
• Nebulized hypertonic saline may help in some settings, but evidence is mixed and it is not universally endorsed 15 16 17.
• Chest physiotherapy is not recommended 3 14 16.

Special Considerations

• Inhaled adrenaline (epinephrine) may be used in emergency settings for significant airway obstruction, but routine use is not supported by strong evidence 16 17.
• In rare cases where respiratory failure develops, non-invasive or invasive ventilation may be necessary 17.

Prevention

• Palivizumab, a monoclonal antibody, can be used as prophylaxis during RSV season for high-risk infants (premature, chronic lung or heart disease, immunodeficient) 3 6 16.
• Environmental measures include hand hygiene, avoiding exposure to sick contacts, and minimizing tobacco smoke exposure 3 16.

Hospitalization Criteria

Children should be hospitalized if they:

• Have oxygen saturation below 90–92%
• Show moderate to severe respiratory distress
• Are unable to maintain hydration
• Have recurrent apnea
• Have underlying risk factors (e.g., prematurity, cardiac or pulmonary disease) 16

Conclusion

Bronchiolitis is a complex and dynamic illness, especially in infants and young children. While most cases are mild and self-limited, some children develop severe disease requiring intensive supportive care. Research continues to refine our understanding of its diverse clinical presentations, causes, and best practices for management.

Key Takeaways:

• Symptoms: Start with cold-like symptoms, may progress to wheezing, tachypnea, and severe respiratory distress 1 3 16.
• Types: Multiple phenotypes exist—RSV and rhinovirus are most common, with varying severity and long-term risks 3 4 6 9.
• Causes: Primarily viral (RSV, rhinovirus); risk factors like prematurity and heart/lung disease increase severity 3 6 16.
• Treatment: Supportive care is central. Oxygen, hydration, and minimal handling are key; most medications (bronchodilators, steroids, antibiotics) offer little benefit 3 13 14 16.
• Prevention: Focus on hygiene and RSV prophylaxis for high-risk groups 3 6 16.

Empowering caregivers and clinicians with up-to-date, evidence-based information on bronchiolitis promotes better outcomes for infants and young children everywhere.