Viral bronchiolitis in children: symptoms, diagnosis, treatment and prevention

Viral bronchiolitis is an acute viral infection of the lower respiratory tract, causing inflammation and swelling of the smallest airways, or bronchioles. The disease most often develops in children under 2 years of age, particularly in the first year of life, with peak incidence occurring between 3 and 6 months of age. In clinical practice, it is one of the most common reasons for infants seeking medical attention and hospitalization for respiratory failure during the respiratory virus season. [1]

Bronchiolitis most often begins as a common viral upper respiratory tract infection. NICE describes the typical course as follows: 1-3 days of runny nose and catarrhal symptoms, followed by persistent cough, tachypnea, or chest indrawing, and wheezing, crepitations, or a combination of both. Symptoms typically peak on days 3-5 of illness. [2]

The main causative virus is respiratory syncytial virus. According to the World Health Organization, it remains one of the leading causes of acute lower respiratory tract infections in children, causing more than 3.6 million hospitalizations and approximately 100,000 deaths in children under 5 years of age annually, with infants under 6 months of age being particularly vulnerable. Almost all children become infected by the virus by age 2, but not all develop severe infections. [3]

Although respiratory syncytial virus is the leading cause, other viruses also cause bronchiolitis. Recent reviews list human metapneumovirus, parainfluenza viruses, rhinoviruses, adenoviruses, influenza viruses, coronaviruses, and several other respiratory pathogens as significant causes. This is important because the clinical syndrome is typically similar, and treatment strategies in most cases remain similarly supportive. [4]

The particular clinical significance of bronchiolitis is related to the patient's age. In infants, nasal breathing and the ability to maintain feeding depend on airway patency to a much greater extent than in older children. Therefore, even moderate bronchial edema, mucus, and rapid breathing quickly lead to feeding difficulties, dehydration, hypoxemia, and sometimes apnea. In children under 6 weeks old, the disease may begin with apnea, without the typical "cold" symptoms. [5]

What characterizes viral bronchiolitis?	Practical meaning
Age up to 2 years, especially the first year of life	Babies are the most vulnerable
Catarrhal prodrome 1-3 days	The disease often begins as a common cold.
Then cough, tachypnea, retractions, wheezing or crepitations	A typical clinical picture is formed
Peak symptoms on day 3-5	During this period, re-evaluation is more often required.
The main causative agent is the respiratory syncytial virus.	But not the only one

Source of the table. [6]

How common is it and who gets it more severely?

Viral bronchiolitis is one of the most common respiratory diseases of infancy. StatPearls indicates that it is one of the most common causes of illness and hospitalization in children 2 years and younger, and clinical guidelines from the Royal Children's Hospital Melbourne emphasize that in real-world pediatric practice, it is typically diagnosed in children under 12 months. [7]

Globally, the respiratory syncytial virus (RSV) poses the greatest burden. The World Health Organization reports that it causes approximately 3.6 million hospitalizations in children under 5 years of age each year, and about half of the deaths occur in infants under 6 months. This clearly demonstrates why bronchiolitis is considered more than just a "common cold" but a major childhood health problem. [8]

Even after the introduction of new preventative measures, infants remain the group with the highest rate of hospitalization. According to the United States Centers for Disease Control and Prevention, during the 2024-2025 season, the highest rates of hospitalization associated with respiratory syncytial virus remained in children aged 0-11 months, and an interim assessment showed a 28%-43% reduction in hospitalization rates in infants aged 0-7 months compared to pre-prevention seasons. This means that prevention is already working, but the clinical significance of the disease remains very high. [9]

The highest risk of severe progression is associated not only with age but also with certain underlying conditions. The updated 2025 Australasian guidelines and the Royal Children's Hospital Melbourne guidelines list prematurity, small for gestational age, age less than 10 weeks, chronic lung disease, congenital heart defects, chronic neurological conditions, immunodeficiency, failure to thrive, trisomy 21, and exposure to tobacco smoke as factors associated with more severe progression. [10]

Severe bronchiolitis can also occur in children without significant underlying medical conditions. A 2025 study in JAMA Network Open found that among children under 2 years of age, a more severe course of the disease was particularly associated with age under 6 months and prematurity, but a significant proportion of hospitalized children had no severe chronic medical conditions at all. This is an important practical point: the absence of a serious diagnosis in the medical history does not guarantee a mild course of bronchiolitis in an infant. [11]

Risk factor for severe course	Why is it important?
Age under 3 months	Highest risk of hypoxemia, apnea and hospitalization
Age 3-6 months	The risk of severe disease remains high.
Prematurity	Less respiratory reserve
Chronic lung and heart diseases	Decompensation develops more quickly
Neurological diseases and immunodeficiency	It is more difficult to clear the airways and transmit infection
Tobacco smoke	Increases the severity of symptoms and worsens outcomes

Source of the table. [12]

Why does bronchiolitis develop and how exactly does it impair breathing?

Most viruses first enter the nasopharyngeal mucosa and then descend into the lower respiratory tract. StatPearls describes that respiratory syncytial virus, after initial replication in the nasopharynx, disseminates to the cells of the terminal bronchioles. This dissemination typically takes 1-3 days after the onset of upper respiratory symptoms, which explains the characteristic transition from a runny nose to shortness of breath and cough. [13]

When the virus reaches the bronchioles, it causes epithelial damage and a local inflammatory response. Swollen mucus, cellular debris, and viscous secretions accumulate in the small airways. The lumen of the bronchioles in infants is initially very narrow, so even mild swelling leads to a significant increase in breathing resistance. This is why the child develops rapid breathing, chest indrawing, and wheezing. [14]

An additional problem is created by the phenomenon of air trapping. Air can still partially enter the small airways, but exiting them is less efficient. This increases the work of breathing, increases the use of accessory muscles, and increases the risk of exhaustion. In severe cases, the process progresses to hypoxemia and respiratory failure, requiring oxygen support or more intensive respiratory therapy. [15]

For some children, the main early complication is not so much hypoxemia as feeding difficulties. NICE and PREDICT guidelines note that poor feeding often develops on days 3-5 of illness and becomes one of the most common reasons for hospitalization. This is critical for the infant: due to rapid breathing, nasal congestion, and fatigue, they are unable to feed properly and rapidly lose fluid. [16]

In very young children, bronchiolitis sometimes presents with apnea. NICE specifically warns that infants under 6 weeks old may present with respiratory arrest without any obvious typical signs. Therefore, at this age, even a seemingly "not very severe" onset of infection requires more vigilant monitoring. [17]

What happens in the airways	How does this manifest itself?
The virus descends from the nasopharynx into the bronchioles	A runny nose gives way to a cough and shortness of breath
Mucosal swelling and inflammation	The lumen of the small airways narrows
Accumulation of mucus and cellular debris	Wheezing and difficulty exhaling appear
Air trap	The work of breathing increases
Fatigue and feeding difficulties	The risk of dehydration is increasing
Apnea in young infants	This may be the first dangerous symptom.

Source of the table. [18]

Symptoms, red flags, and possible complications

Typical bronchiolitis begins with a runny nose, followed by cough, rapid breathing, chest indrawing, and wheezing. NICE adds that fever occurs in approximately 30% of cases and typically does not exceed 39°C (102°F), and cough resolves within 90% of infants within 3 weeks. This dynamic helps differentiate bronchiolitis from some other childhood respiratory conditions. [19]

As the illness progresses, parents typically notice that their child eats less, tires more quickly, sleeps less well, and becomes more irritable or, conversely, lethargic. In severe cases, nasal flaring, pronounced intercostal retractions, grunting, cyanosis around the mouth, and a noticeable decrease in the number of wet diapers appear. This is no longer just a "cough and runny nose," but rather signs of respiratory and hydration compromise. [20]

NICE recommends that children be referred for emergency care immediately if they experience apnea, appear seriously ill, show significant respiratory distress with a respiratory rate greater than 70 breaths per minute, or have central cyanosis. Additionally, hospital evaluation should be considered if the respiratory rate is greater than 60 breaths per minute, fluid intake is reduced to 50%-75% of normal, clinical dehydration, or persistently decreased oxygen saturation. [21]

For parents who are allowed to treat their child at home, NICE specifically lists red flags: deteriorating respiratory function, fluid intake of only 50%-75% of the usual amount, or the absence of a wet diaper for 12 hours, apnea or cyanosis, and exhaustion, where the child is less responsive to others and awakens only with prolonged stimulation. These are very practical criteria for re-admission, especially in the first 5 days of illness, when symptoms typically worsen. [22]

Most children recover without serious sequelae, but complications are still possible. StatPearls classifies acute complications as respiratory failure, apnea, aspiration, secondary bacterial infection, and, in rare cases, death. Later complications include recurrent episodes of wheezing, and the association with the subsequent development of asthma is debated, although the causal role of bronchiolitis itself remains unclear. [23]

Symptom or sign	How to interpret it
Runny nose, cough, tachypnea, wheezing	Typical initial picture of bronchiolitis
Poor feeding	A common cause of deterioration and hospitalization
Chest retractions, grunting	Significant respiratory load
Apnea, cyanosis, severe lethargy	An urgent reason for emergency care
No wet diaper for 12 hours	Possible dehydration
Recurrence of wheezing in the future	Possible late consequences in some children

Source of the table. [24]

How is the diagnosis made and what is important not to confuse?

Bronchiolitis remains primarily a clinical diagnosis. NICE, the Royal Children's Hospital Melbourne, and StatPearls agree: with a typical presentation, laboratory confirmation of the virus is usually unnecessary, and the decision is based on the child's age, characteristic prodrome, cough, tachypnea, indrawings, and auscultatory changes. This is an important principle, as overdiagnosis does not improve outcome but often overburdens the child and the care system. [25]

Pulse oximetry is necessary for all children with suspected bronchiolitis, but its results must be interpreted judiciously. NICE recommends measuring oxygen saturation in every child with suspected bronchiolitis and specifically warns that pulse oximetry may be less accurate at borderline values, including possible overestimation in people with dark skin. Furthermore, brief desaturations during sleep do not, by themselves, indicate the need for oxygen. [26]

Routine blood tests, chest X-rays, and viral tests are generally not recommended. NICE specifically states that routine blood tests and chest X-rays should not be performed because radiographic changes can mimic pneumonia and lead to unnecessary antibiotic prescriptions. The 2025 Australasian Guidelines also advise against routine virological testing and laboratory testing unless there is an atypical presentation, severe illness, or suspicion of a bacterial complication. [27]

Differential diagnosis is particularly important in older children and those with atypical presentations. NICE recommends considering pneumonia if a temperature above 39°C (102.4°F) and persistent focal crackling wheezes are present, and virus-induced wheezing or early asthma if an older infant or young child has persistent wheezing without crackles, recurrent wheezing episodes, or a significant personal or family history of atopy. StatPearls also recommends distinguishing bronchiolitis from foreign body aspiration, aspiration pneumonia, gastroesophageal reflux, anaphylaxis, and congenital airway anomalies. [28]

From a practical standpoint, a diagnosis can be thought of as answering three questions. First: is this truly typical bronchiolitis? Second: how severe is it right now? Third: is this symptom concealing pneumonia, an asthma-like episode, sepsis, or another pathology requiring different treatment? This is why a thorough examination and reassessment within a few hours is often more valuable than running too many tests. [29]

Diagnostic question	A modern answer
Do all children need a smear or viral test?	No, usually the diagnosis is clinical.
Is pulse oximetry necessary?	Yes, but the result is assessed in the context of the child's condition
Do all children need x-rays?	No, it is not routinely indicated.
Are routine blood tests necessary?	No, they are not indicated in the typical course of treatment.
What most often has to be excluded	Pneumonia, early asthma, aspiration, foreign body, sepsis

Source of the table. [30]

Treatment: What really helps and what is usually unnecessary

The main principle of treating viral bronchiolitis is supportive care. NICE, the updated 2025 Australasian Guidelines, and the Royal Children's Hospital Melbourne agree that the foundation of care is maintaining oxygenation, adequate fluid intake, and minimizing unnecessary interventions. This means that a good outcome is often achieved not by "strong drugs," but by competent monitoring, oxygen as indicated, and correction of dehydration. [31]

Oxygen is indicated not for any dyspnea, but for persistent hypoxemia. NICE recommends giving oxygen to children 6 weeks and older with persistent oxygen saturation below 90%, and to children under 6 weeks and children of any age with underlying illnesses with persistent oxygen saturation below 92%. The 2025 Australasian Guidelines use the same guidelines and specifically emphasize that brief episodes of decreased oxygen saturation, especially during sleep, should not automatically trigger oxygen therapy. [32]

High-flow oxygen therapy should not be a routine first-line therapy. The updated 2025 Australasian Guidelines explicitly advise against its routine use in non-hypoxemic children with mild to moderate bronchiolitis and against its immediate use as a first step in moderate hypoxemic cases. It is suggested to consider it if the child has hypoxemia and does not respond to low-flow oxygen therapy, or if the course is initially severe. The Royal Children's Hospital Melbourne uses the same logic: low-flow oxygen first, then high-flow support if this is ineffective. [33]

If respiratory failure threatens, more intensive respiratory support may be required. NICE recommends considering continuous positive airway pressure (CPAP) for impending respiratory failure, and the Australasian Guidelines indicate that CPAP can be used in children with severe illness or severe respiratory failure. This therapy is reserved for more severely ill patients and hospital-based observation. [34]

Hydration is the second pillar of treatment. If a child is unable to maintain adequate fluid intake on their own, additional fluid administration is required. NICE recommends using the nasogastric or orogastric route if the child is not drinking enough, and intravenous isotonic fluids if nasogastric feeding is not tolerated or there is already impending respiratory failure. The 2025 Australasian Guidelines also consider both the nasogastric and intravenous routes acceptable, but recommend the nasogastric route as the preferred first option. [35]

However, overfeeding and excessive fluid intake are not recommended. The Australasian guidelines emphasize the risk of increased antidiuretic hormone secretion and hyponatremia in children with bronchiolitis, so when providing additional fluids, monitoring for signs of both dehydration and fluid overload is essential. This is an important reason why even "simple" fluid resuscitation in severely ill infants requires careful consideration. [36]

Superficial nasal suctioning may be used sparingly if mucus interferes with feeding or increases respiratory distress. NICE recommends against routine suctioning, but allows it if mucus makes feeding or breathing difficult, as well as in cases of apnea. The 2025 Australasian Guidelines also discourage routine, particularly deep, suctioning, but allow superficial nasal clearance in cases of respiratory distress and feeding difficulties. [37]

What parents often expect, but usually don't help, are bronchodilators, adrenaline, steroids, antibiotics, and hypertonic saline. NICE explicitly lists drugs and interventions that should not be used routinely: antibiotics, hypertonic saline, nebulized adrenaline, salbutamol, montelukast, ipratropium bromide, systemic and inhaled corticosteroids, and the combination of adrenaline and steroids. The 2025 Australasian guideline endorses the avoidance of beta-2 agonists, adrenaline, glucocorticoids, hypertonic saline, and antibiotics in routine practice. [38]

Why is this important? Because bronchiolitis is not classic asthma or bacterial pneumonia. Overuse of ineffective medications increases treatment costs, creates a false sense of active therapy, and sometimes worsens the condition through unnecessary side effects and delays in truly beneficial interventions, such as oxygenation, feeding, and monitoring. This is why current guidelines worldwide consistently "eliminate" unnecessary medications from bronchiolitis. [39]

Home treatment is possible if the child is clinically stable, drinking adequate fluids, has no dangerous episodes of apnea, and does not require oxygen. The 2025 Australasian Guidelines for Safe Discharge recommend taking into account respiratory stability, feeding at least half the usual amount, the family's ability to notice deterioration, social conditions, and the ability to return quickly for help. NICE provides similar guidelines and specifically emphasizes the need for a written or electronic reminder for parents. [40]

What really works in treatment	What is not usually recommended routinely
Maintaining oxygenation at saturation thresholds	Salbutamol and other beta-2 agonists
Nasogastric or intravenous hydration as indicated	Adrenalin
Superficial suction of secretions during feeding and severe congestion	Systemic and inhaled steroids
High-flow oxygen therapy after failure of low-flow oxygen therapy	Antibiotics without signs of bacterial infection
Continuous positive airway pressure in severe cases	Hypertonic solution
Teaching parents about signs of deterioration	Routine chest physiotherapy

Source of the table. [41]

Prevention, prognosis, and what has changed in recent years

Prevention begins with simple anti-epidemic measures. The World Health Organization and StatPearls emphasize the importance of hand hygiene, reducing infants' contact with people with symptoms of infection, protecting against tobacco smoke, and promptly vaccinating others against influenza and other respiratory infections, if indicated for their age and country of residence. This is especially important for infants, as the risk of severe illness is highest in the first months of life. [42]

The most notable change in recent years is the emergence of effective prophylaxis against severe respiratory syncytial virus (SRSV) in infants. In 2025, the World Health Organization (WHO) issued its first position paper recommending that countries implement either the maternal vaccine during pregnancy or the long-acting monoclonal antibody nirsevimab, depending on the capacity of their health systems. The WHO states that nirsevimab begins protecting the infant within a week and lasts for at least five months, while the maternal vaccine is administered in the third trimester of pregnancy. [43]

The United States Centers for Disease Control and Prevention also recommends that all infants be protected from severe respiratory syncytial virus infection by 2025 through one of two routes: maternal vaccination during pregnancy or long-acting antibody administration to the infant. Most infants do not require both options. This strategy is especially important because severe respiratory syncytial virus infection remains the leading cause of viral bronchiolitis and hospitalization in infants. [44]

The prognosis for most children is good. NICE reports that symptoms typically peak at 3-5 days, and cough resolves within 3 weeks in 90% of infants. StatPearls adds that most children recover within 5-7 days, although a residual cough may persist longer. This means that even after breathing improves, full clinical recovery often does not occur within 1-2 days. [45]

However, this disease cannot be considered completely harmless. Severe episodes are associated with apnea, respiratory failure, dehydration, and rare fatalities, especially in premature infants and infants with underlying medical conditions. Furthermore, after bronchiolitis, some children experience repeated episodes of wheezing, although a direct causal link to subsequent asthma remains debated. Therefore, the goal of modern prevention is not only to cure an already infected child but also to minimize the likelihood of a severe first season of respiratory syncytial virus infection. [46]

Prevention direction	What really helps
Household prevention	Hand washing, reducing contact with sick people, and avoiding tobacco smoke
Protecting infants from respiratory syncytial virus	Maternal vaccination or long-acting monoclonal antibody
Early assessment of severe disease	Special attention should be given to children under 3 months and premature babies.
Parent training	Understanding red flags and peak symptom timing
Post-discharge follow-up	Monitoring of feeding, respiration and saturation as indicated

Source of the table. [47]

FAQ

Are antibiotics necessary for viral bronchiolitis?
Usually not. Current guidelines advise against the routine use of antibiotics because bronchiolitis is a viral, not bacterial, disease. Exceptions are possible only in the case of compelling evidence of a bacterial complication. [48]

Is salbutamol needed if wheezing is heard?
Usually not. Wheezing associated with bronchiolitis does not necessarily indicate asthma. NICE and the updated 2025 Australasian guidelines do not recommend the routine use of salbutamol and other beta-2 agonists in infants with bronchiolitis. [49]

When is a child most likely to be hospitalized?
When they have apnea, severe respiratory distress, persistent hypoxemia, dehydration, poor fluid intake, are under 6 weeks old, or have significant underlying medical conditions. Social situation is also important: if it is difficult for the family to quickly return for help, the hospitalization threshold is lower. [50]

Should a chest X-ray be performed?
Routinely, no. It can mimic pneumonia and lead to unnecessary antibiotic administration. A chest X-ray is considered in cases of atypical presentation, diagnostic uncertainty, or very severe illness. [51]

Is it possible to treat a child at home?
Yes, if the child's breathing is relatively stable, the child is drinking enough, there is no apnea, severe cyanosis, or persistent hypoxemia, and the family understands when it is time to seek emergency medical attention. [52]

Is it true that the new seasonal vaccine can protect infants from severe bronchiolitis?
For bronchiolitis caused by respiratory syncytial virus, yes. The World Health Organization and the United States Centers for Disease Control and Prevention recommend strategies to prevent severe infection in infants through maternal vaccination during pregnancy or long-acting monoclonal antibodies given to the infant. [53]

Key points from experts

Professor Franz Babl, Professor of Paediatric Emergency Medicine at the University of Melbourne, Director of Emergency Research at the Murdoch Institute of Child Research, and a paediatric emergency physician at the Royal Children's Hospital Melbourne, is a member of the PREDICT network and a contributor to the 2025 Australasian Guidelines update. His work reflects a key contemporary philosophy: bronchiolitis should be managed using the most evidence-based approach, eliminating unnecessary tests and medications and focusing on oxygenation, hydration, and timely escalation of respiratory support. [54]

Professor Stuart Dalziel, Professor of Paediatrics and Emergency Medicine at the University of Auckland, Director of Emergency Medicine Research at Starship Children's Hospital, and Chair of Child Health Research at Cure Kids, highlights two key ideas: diagnosis is usually clinical, and treatment should generally focus on supporting breathing and nutrition, avoiding routine use of ineffective interventions. [55]

Professor Meredith Borland, Director of Emergency Medicine at Perth Children's Hospital, a pediatric emergency physician, and Associate Professor at the University of Western Australia School of Medicine is a key member of the PREDICT network. Her clinical perspective is particularly relevant for hospital practice: high-flow oxygen therapy is not beneficial for everyone, but should be used judiciously after assessing hypoxemia and the response to low-flow oxygen support. [56]

Conclusion

Viral bronchiolitis is one of the most common and most underestimated causes of severe respiratory distress in infants. In most cases, the disease resolves spontaneously, but it is the first months of life, prematurity, poor feeding, apnea, and persistent hypoxemia that make it potentially dangerous. Therefore, the primary task of the physician and family is not to seek a "strong cure," but to correctly assess the severity, promptly support breathing and hydration, and not miss the moment when the child already requires hospitalization. [57]

The most significant change of recent years is the availability of preventative measures against severe respiratory syncytial virus infection. This does not negate supportive treatment for children already infected, but it does reduce the number of hospitalizations and severe episodes in the most vulnerable age group. Given that bronchiolitis remains one of the leading causes of infant hospitalization, this is perhaps the most significant practical achievement of recent years. [58]