Bronchiolitis is a common lung infection in young children and infants. It causes congestion in the small airways (bronchioles) of the lung. Bronchiolitis is almost always caused by a virus. Typically, the peak time for bronchiolitis is during the winter months.
Bronchiolitis starts out with symptoms similar to those of a common cold but then progresses to coughing, wheezing and sometimes difficulty breathing. Symptoms of bronchiolitis can last for several days to weeks, even a month.
Most children get better with supportive care at home. A very small percentage of children require hospitalization.
Bronchiolitis is almost always caused by a viral infection. In most cases, the respiratory syncytial virus (RSV) is responsible.
RSV is a very common virus and almost all children are infected with it by the time they’re two years old. In older children and adults, RSV may cause a cough or cold, but in young children it can cause bronchiolitis.
Bronchioles are small airways (< 2 mm in diameter) and lack cartilage and submucosal glands. The terminal bronchiole, a 16th-generation airway, is the final conducting airway that terminates in the respiratory bronchioles. The acinus (ie, the gas exchange unit of the lung) consists of respiratory bronchioles, the alveolar duct, and alveoli. The bronchiolar lining consists of surfactant-secreting Clara cells and neuroendocrine cells, which are the source of bioactive products such as somatostatin, endothelin, and serotonin.
Bronchiolar injury and the consequent interplay between inflammatory and mesenchymal cells can lead to diverse pathologic and clinical syndromes. The effects of bronchiolar injury include the following:
- Increased mucus secretion
- Bronchial obstruction and constriction
- Alveolar cell death, mucus debris, viral invasion
- Air trapping
- Reduced ventilation that leads to ventilation-perfusion mismatch
- Labored breathing
Complex immunologic mechanisms play a role in the pathogenesis of bronchiolitis. Type 1 allergic reactions mediated by immunoglobulin E (IgE) may account for some clinically significant bronchiolitis. Infants who are breastfed with colostrum rich in immunoglobulin A (IgA) appear to be relatively protected from bronchiolitis.
Necrosis of the respiratory epithelium is one of the earliest lesions in bronchiolitis and occurs within 24 hours of acquisition of infection.Proliferation of goblet cells results in excessive mucus production, whereas epithelial regeneration with nonciliated cells impairs elimination of secretions. Lymphocytic infiltration may result in submucosal edema.
Cytokines and chemokines, released by infected respiratory epithelial cells, amplify the immune response by increasing cellular recruitment into infected airways. Interferon and interleukin (IL)–4, IL-8, and IL-9 are found in high concentrations in respiratory secretions of infected patients.
Johnson et al analyzed autopsy findings from children who died of possible RSV infection between 1925 and 1959 (before modern intensive care) and those from a child with RSV bronchiolitis who died in a motor vehicle accident. They found that small bronchiole epithelium was circumferentially infected but basal cells were spared. Both type 1 and type 2 alveolar pneumocytes were also infected.
In this study, airway obstruction was due to epithelial and inflammatory cell debris mixed with fibrin, mucus, and edema fluid but not to bronchial smooth muscle constriction. Other research revealed that neutrophil inflammation, but not eosinophil inflammation, is related to the severity of a first infection in infants.
The inflammation, edema, and debris result in obstruction of bronchioles, leading to hyperinflation, increased airway resistance, atelectasis, and ventilation-perfusion mismatching. Bronchoconstriction has not been described.
Infants are affected most often because of their small airways, high closing volumes, and insufficient collateral ventilation. Recovery begins with regeneration of bronchiolar epithelium after 3-4 days; however, cilia do not appear for as long as 2 weeks. Mucus plugs are predominantly removed by macrophages.
Infection is spread by direct contact with respiratory secretions. In the United States, epidemics last 2-4 months, beginning in November and peaking in January or February. Whereas 93% of cases occur between November and early April, sporadic cases may occur throughout the year. Attack rates within families are as high as 45% and are higher in childcare centers. Rates of hospital-acquired infection range from 20-47%.
Virtually all children experience RSV infection within the first 3 years of life, but previous infection does not convey complete immunity. Reinfection is common; however, significant antibody titers from previous infection ameliorate the severity of symptoms.
For the first few days, the signs and symptoms of bronchiolitis are similar to those of a common cold:
- Runny nose
- Stuffy nose
- Slight fever (not always present)
After this, there may be a week or more of breathing difficulty or a whistling noise when breathing out (wheezing).
Many infants will also have an ear infection (otitis media).
Your GP will ask about your child’s symptoms – for example, whether they’ve had a runny nose, cough or high temperature (fever) and for how long.
They’ll also listen to your child’s breathing using a stethoscope, to check for any crackling or high-pitched wheezing as your child breathes in and out.
If your child hasn’t been feeding very well or has been vomiting, your GP may also look for signs of dehydration, which include:
- a dipped fontanelle (the soft spot on the top of the head) in babies
- dry mouth and skin
- producing little or no urine
Your GP may recommend that your child is admitted to hospital if they aren’t feeding properly and are dehydrated, or they’re having problems breathing.
Further tests for bronchiolitis aren’t usually necessary. However, as some conditions cause similar symptoms to bronchiolitis, such ascystic fibrosis and asthma, tests may be needed.
If it isn’t clear what’s causing your child’s symptoms, or your child hassigns of severe bronchiolitis, your GP may recommend further tests in hospital to help confirm the diagnosis.
THESE TESTS MIGHT INCLUDE:
a mucus sample test –a sample of mucus from your child’s nose will be tested to identify the virus causing their bronchiolitis
Urine Or Blood Tests
a pulse oximeter test –a small electronic device is clipped to your child’s finger or toe to measure the oxygen in their blood
The vast majority of cases of bronchiolitis can be cared for at home with supportive care. Make sure your child is getting adequate liquids. Consider saline nose drops or suctioning with a bulb to relieve nasal congestion. Be alert for changes in breathing difficulty. Expect the condition to last for a week to a month.
Drugs that open the airways (bronchodilators) haven’t been found to be routinely helpful. But your doctor may elect to try a nebulized albuterol treatment to see if it helps.
Because viruses cause bronchiolitis, antibiotics — which are used to treat infections caused by bacteria — aren’t effective against it. If your child has an associated bacterial infection, such as pneumonia, your doctor may prescribe an antibiotic for that.
Use of corticosteroid medications, the antiviral drug ribavirin and pounding on the chest to loosen mucus (chest physiotherapy) have not been shown to be effective treatments for bronchiolitis and are not recommended.
A tiny percentage of children need hospital care to manage their condition. At the hospital, your child will likely receive humidified oxygen to maintain sufficient oxygen in the blood, and perhaps fluids through a vein (intravenously) to prevent dehydration. In severe cases, a tube may be inserted into the windpipe (trachea) to help the child’s breathing.