Bronchiolitis is blockage of the small airways in the lungs due to a viral infection. It usually only occurs in children less than two years of age. Symptoms may include fever, cough, runny nose, wheezing, and breathing problems. More severe cases may be associated with nasal flaring, grunting, or the skin between the ribs pulling in with breathing. If the child has not been able to feed properly, signs of dehydration may be present.
Bronchiolitis is the leading cause of hospitalizations among infants less than one year of age. About 10% to 30% of children under the age of two years are affected by bronchiolitis at some point in time. It more commonly occurs in the winter in the Northern hemisphere. The risk of death among those who are admitted to hospital is about 1%. Outbreaks of the condition were first described in the 1940s.
Bronchiolitis typically presents in children under two years old and is characterized by a constellation of respiratory symptoms that consists of fever, rhinorrhea, cough, wheeze, tachypnea and increased work of breathing such as nasal flaring or grunting that develops over one to three days.Crackles or wheeze are typical findings on listening to the chest with a stethoscope. The child may also experience apnea, or brief pauses in breathing. After the acute illness, it is common for the airways to remain sensitive for several weeks, leading to recurrent cough and wheeze.
Children born prematurely (less than 35 weeks), with a low birth weight or who have congenital heart disease may have higher rates of bronchiolitis and are more likely to require hospital admission. There is evidence that breastfeeding provides some protection against bronchiolitis.
Children are at an increased risk for progression to severe respiratory disease if they have any of the following additional factors: 
The diagnosis is typically made by clinical examination. Chest X-ray is sometimes useful to exclude bacterial pneumonia, but not indicated in routine cases.
Testing for the specific viral cause can be done but has little effect on management and thus is not routinely recommended. RSV testing by direct immunofluorescence testing on nasopharyngeal aspirate had a sensitivity of 61% and specificity of 89%. Identification of those who are RSV-positive can help for: disease surveillance, grouping ("cohorting") people together in hospital wards to prevent cross infection, predicting whether the disease course has peaked yet, reducing the need for other diagnostic procedures (by providing confidence that a cause has been identified).
Infants with bronchiolitis between the age of two and three months have a second infection by bacteria (usually a urinary tract infection) less than 6% of the time. Preliminary studies have suggested that elevated procalcitonin levels may assist clinicians in determining the presence of bacterial coinfection, which could prevent unnecessary antibiotic use and costs.
Prevention of bronchiolitis relies strongly on measures to reduce the spread of the viruses that cause respiratory infections (that is, handwashing, and avoiding exposure to those symptomatic with respiratory infections). In addition to good hygiene, an improved immune system is a great tool for prevention. One way to improve the immune system is to feed the infant with breast milk, especially during the first month of life.Immunizations are available for premature infants who meet certain criteria (some cardiac and respiratory disorders) such as palivizumab (a monoclonal antibody against RSV). Passive immunization therapy requires monthly injections during winter.
Treatment of bronchiolitis is usually focused on the symptoms instead of the infection itself since the infection will run its course and complications are typically from the symptoms themselves. Without active treatment, half of cases will go away in 13 days and 90% in three weeks.
Current guidelines currently recommend against the use of bronchodilators in children with bronchiolitis as evidence does not support a change in outcomes with such use.
Several studies have shown that bronchodilation with β-adrenergic agents such as albuterol may improve clinical symptoms briefly but do not affect the overall course of the illness or reduce the need for hospitalization. However, there are conflicting recommendations about the use of a trial of a bronchodilator, especially in those with history of previous wheezing, due to the difficulty with assessing an objective improvement in symptoms.  Additionally, there are adverse effects to the use of bronchodilators in children such as tachycardia and tremors as well as adding increased expense. 
The current state of evidence suggests that nebulizedepinephrine is not indicated for children with bronchiolitis except as a trial of rescue therapy for severe cases.
Epinephrine is an α and β adrenergic agonist that has been used to treat other upper respiratory tract illnesses, such as croup, as a nebulized solution. A Cochrane meta-analysis in 2011 found no benefit to the use of epinephrine in the inpatient setting and suggested that there may be utility in the outpatient setting in reducing the rate of hospitalization. However, current guidelines do not support the outpatient use of epinephrine given the lack of substantial benefit as well as concerns over the medicine's transient effect and subsequent risk of progression of the illness in an unsupervised setting.
A 2017 review found inhaled epinephrine with corticosteroids did not change the need for hospitalization or the time spent in hospital.
Nebulizedhypertonic saline (3%) has tentative evidence of benefit. A 2017 review found tentative evidence that it reduces the risk of hospitalization, duration of hospital stay, and improved the severity of symptoms. Side effects were mild and resolved spontaneously. Routine use was not recommended due to the low quality of the evidence.
Currently other medications do not yet have evidence to support their use, although they have been studied for use in bronchiolitis.Ribavirin is an antiviral drug which does not appear to be effective for bronchiolitis.Antibiotics are often given in case of a bacterial infection complicating bronchiolitis, but have no effect on the underlying viral infection and their benefit is not clear.Corticosteroids have no proven benefit in bronchiolitis treatment and are not advised.DNAse has not been found to be effective.
Bronchiolitis typically affects infants and children younger than two years, principally during the fall and winter . Bronchiolitis hospitalization has a peak incidence between two and six months of age and remains a significant cause of respiratory disease during the first two years of life.
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