Bronchiolitis


Bronchiolitis is inflammation of the small airways also known as the bronchioles in the lungs. Acute bronchiolitis is caused by a viral infection, usually affecting children younger than two years of age. Symptoms may include fever, cough, runny nose or rhinorrhea, and wheezing. More severe cases may be associated with nasal flaring, grunting, or respiratory distress. If the child has not been able to feed properly due to the illness, signs of dehydration may be present.
Chronic bronchiolitis is more common in adults and has various causes, one of which is bronchiolitis obliterans. Often when people refer to bronchiolitis, they are referring to acute bronchiolitis in children.
Acute bronchiolitis is usually the result of viral infection by respiratory syncytial virus or human rhinovirus. Diagnosis is generally based on symptoms. Tests such as a chest X-ray or viral testing are not routinely needed, but may be used to rule out other diseases.
There is no specific medication that is used to treat bronchiolitis. Symptomatic treatment at home is generally effective and most children do not require hospitalization. This can include antipyretics such as acetaminophen for fever and nasal suction for nasal congestion, both of which can be purchased over the counter. Occasionally, hospital admission for oxygen, particularly high flow nasal cannula, or intravenous fluids is needed in more severe cases of disease.
About 10% to 30% of children under the age of two years are affected by bronchiolitis at some point in time. It commonly occurs in the winter season in the Northern Hemisphere. It is the leading cause of hospitalizations in those less than one year of age in the United States. The risk of death among those who are admitted to hospital is extremely low at about 1%. Outbreaks of the condition were first described in the 1940s.

Signs and symptoms

Bronchiolitis typically presents in children under two years old and is characterized by symptoms of a respiratory illness, sometimes referral to as a viral prodrome.Signs of the disease include:
Some signs of severe disease include:
  • increased work of breathing
  • severe chest wall recession
  • presence of nasal flaring and/or grunting
  • severe tachypnea or increased breathing
  • hypoxia
  • cyanosis
  • lethargy and decreased activity
  • poor feeding
These symptoms can develop over one to three days. Crackles or wheeze are typical findings on listening to the chest with a stethoscope. Wheezes can occasionally be heard without a stethoscope. The child may also experience apnea, or brief pauses in breathing, but this can occur due to many conditions that are not just bronchiolitis. After the acute illness, it is common for the airways to remain sensitive for several weeks, leading to recurrent cough and wheeze.

Causes

Bronchiolitis is most commonly caused by respiratory syncytial virus. Other agents that cause this illness include, but are not limited to, human metapneumovirus, influenza, parainfluenza, coronavirus, adenovirus, rhinovirus and mycoplasma.

Risk factors

Children are at an increased risk for progression to severe respiratory disease if they have any of the following additional risk factors:
Targeted, community-led, co-produced interventions to alleviate the healthcare burdens of bronchiolitis have been shown to be effective.

Diagnosis

The diagnosis is typically made by a provider through clinical history and physical exam. Chest X-ray is sometimes useful to exclude bacterial pneumonia, but not indicated in routine cases. Chest x-ray may also be useful in people with impending respiratory failure. Additional testing such as blood cultures, complete blood count, and electrolyte analyses are not recommended for routine use although may be useful in children with multiple comorbidities or signs of sepsis or pneumonia. Electrolyte analyses may be performed if there is concern for dehydration.
File:RSV.PNG|thumb|An X-ray of a child with RSV showing the typical bilateral perihilar fullness of bronchiolitis. The arrows are pointing to the portion of the X-ray that is abnormal and shows fluffy perihilar fullness.
Testing for the specific viral cause can be done but has little effect on management and thus is not routinely recommended. The COVID pandemic has led to more viral testing to exclude COVID as a cause of the infection. At that point providers often also add on a flu and RSV test for completeness. RSV testing by direct immunofluorescence testing of a swab of the nose had a sensitivity of 61% and specificity of 89%, so it is not always accurate. Identification of those who are RSV-positive can help providers recommend isolation precautions in the hospital or at home to avoid the infection spreading to others. Identification of the virus may help reduce the use of antibiotics because antibiotics are not recommended for viral illnesses such as bronchiolitis.
It is uncommon for infants with bronchiolitis to be co-infected with a bacterial illness. Infants with bronchiolitis between the age of two and three months have a second infection by bacteria less than 6% of the time. When further evaluated with a urinalysis, infants with bronchiolitis had an accompanying UTI 0.8% of the time.

Differential diagnosis

There are many childhood illnesses that can present with respiratory symptoms, particularly persistent cough, runny nose, and wheezing. Bronchiolitis may be differentiated from some of these by the characteristic pattern of preceding febrile upper respiratory tract symptoms lasting for 1 to 3 days with associated persistent cough, increased work of breathing, and wheezing. However, some infants may present without fever or may present with apnea without other signs or with poor weight gain prior to onset of symptoms. In such cases, additional laboratory testing and radiographic imaging may be useful. The following are some other diagnoses to consider in an infant presenting with signs of bronchiolitis:
Prevention of bronchiolitis relies strongly on measures to reduce the spread of the viruses that cause respiratory infections. Guidelines are mixed on the use of gloves, aprons, or personal protective equipment.
One way to improve the immune system is to feed the infant with breast milk, especially during the first month of life. Respiratory infections were shown to be significantly less common among breastfed infants and fully breastfed RSV-positive hospitalized infants had shorter hospital stays than non or partially breastfed infants. Guidelines recommend exclusive breastfeeding for infants for the first 6 months of life to avoid infection with bronchiolitis.
The US Food and Drug Administration has currently approved two RSV vaccines for adults ages 60 and older, Arexvy and Abrysvo. Abrysvo is also approved for "immunization of pregnant individuals at 32 through 36 weeks gestational age for the prevention of lower respiratory tract disease and severe LRTD caused by respiratory syncytial virus in infants from birth through 6 months of age." It is unclear how effective these vaccines will be in preventing infection with bronchiolitis since they are new, although the FDA has approved them due to the clear benefit that they have shown in clinical trials.
Nirsevimab, a monoclonal antibody against RSV, is approved by the FDA for all children younger than 8 months in their first RSV season. Additionally, children aged 8 to 19 months who are at increased risk may be recommended to receive Nirsevimab as they enter their second RSV season if they have increased risk factors for infection with RSV.
A second monoclonal antibody, Palivizumab, can be administered to prevent bronchiolitis to infants less than one year of age that were born prematurely and that have underlying heart disease or chronic lung disease of prematurity. Otherwise healthy premature infants that were born after a gestational age of 29 weeks should not be administered Palivizumab, as the harms outweigh the benefits.
Tobacco smoke exposure has been shown to increase both the rates of lower respiratory disease in infants, as well as the risk and severity of bronchiolitis. Tobacco smoke lingers in the environment for prolonged periods and on clothing even when smoking outside the home. Guidelines recommend that parents be fully educated on the risks of tobacco smoke exposure on children with bronchiolitis.

Management

Treatment of bronchiolitis is usually focused on the hydration and symptoms instead of the infection itself since the infection will run its course. Complications of bronchiolitis are typically from the symptoms themselves. Without active treatment, cases resolved in approximately eight to fifteen days. Children with severe symptoms, especially poor feeding or dehydration, may be considered for hospital admission. Oxygen saturation under 90%-92% as measured with pulse oximetry is also frequently used as an indicator of need for hospitalization. High-risk infants, apnea, cyanosis, malnutrition, and diagnostic uncertainty are additional indications for hospitalization.
Most guidelines recommend sufficient fluids and nutritional support for affected children along with frequent nasal suctioning. Measures for which the recommendations were mixed include nebulized hypertonic saline, nebulized epinephrine, and chest physiotherapy. Treatments which the evidence does not support include salbutamol, steroids, antibiotics, antivirals, and heliox.