What is bronchiolitis?

Bronchiolitis^[1] is a respiratory infection that causes inflammation and congestion in the small airways of the lungs (called bronchioles). This infection is most common in infants and young children, as their small noses and airways can easily become blocked. Bronchiolitis’ early signs and symptoms are often similar to those of the common cold (another respiratory infection). However, within 2–3 days, bronchiolitis progresses and symptoms worsen. Children can develop serious symptoms, such as wheezing and shallow or rapid breathing. While bronchiolitis is the most common cause for the hospitalization^[2] of children in many countries, it is generally rare that the infection alone requires hospitalization. When trips to the hospital are necessary, they usually only require taking measures to ensure that a child is breathing properly and is sufficiently hydrated.

How common is bronchiolitis?

Bronchiolitis most commonly affects^[3] children under the age of 2, peaking between the ages of 3–6 months. The infection is also more common^[4] in males, children who are born prematurely, children who were not breastfed, and those who live in densely populated or crowded areas. As with the common cold and the flu, instances of bronchiolitis^[5] peak in the fall, winter, and early spring.

Bronchiolitis causes

Viral infection^[6] is the most common cause of bronchiolitis. Among these viruses, respiratory syncytial virus (RSV)^[7] accounts for 60–80% of cases of bronchiolitis in children younger than 12 months old. Aside from RSV, many other viruses may also cause^[8] bronchiolitis, including:

• Rhinovirus
• Human bocavirus
• Parainfluenza
• Adenovirus
• Influenza
• Human metapneumovirus

In 20–30% of cases, bronchiolitis may be caused by more than one virus. However, the presence of additional viral infections does not seem to make the illness more severe. In rare cases, bronchiolitis can be caused by bacteria (specifically, M. pneumoniae). The symptoms of bronchiolitis^[9] resemble those of a bad cold. Unlike colds, which tend to affect the nose and throat (upper respiratory tract), bronchiolitis infections reach the lungs. Bronchiolitis causes the smaller branches of the lungs’ airways (bronchioles) to become swollen and irritated, which can lead to a wheezing or whistling sound while breathing. The virus begins by infecting the upper respiratory tract. It then spreads into the lower respiratory tract, toward the lungs. Aside from causing inflammation, the virus can destroy cells inside the respiratory tract. When this happens, a child’s airflow can become blocked. RSV is highly contagious. According to the CDC^[10], RSV is so common that nearly all children will have had an RSV infection by the age of two. RSV’s peak season usually begins around November and lasts until April or May. RSV can also cause infection in older adults and individuals with weakened immune systems (although these infections would not be considered bronchiolitis). Children who are older than two are not likely to develop bronchiolitis, but they can still be infected with RSV. Some people may be infected more than once by RSV, but subsequent infections are usually milder than the first illness.

Bronchiolitis prognosis

Children may look alarmingly sick when they present with the signs and symptoms of bronchiolitis. Luckily, most children make a complete recovery from the illness within 5–10 days^[11]. Mortality rates for infants without pre-existing conditions or illnesses are low: most studies indicate less than 1% mortality⁸ in such cases. Children who have serious pre-existing cardiorespiratory conditions (such as cystic fibrosis) or are immunocompromised are at higher risk for complications due to bronchiolitis. As such, these groups of children can present mortality rates higher than 30%⁸.

Bronchiolitis symptoms

Both bronchiolitis and the common cold start in the upper respiratory tract. Because of this, the symptoms of bronchiolitis^[12] are similar to those of a cold for the first 1–3 days. Early symptoms include:

• Nasal congestion and discharge (increased mucus production)
• Mild cough
• Fever (a body temperature higher than 100.4°F or 38°C)
• Fatigue
• Decreased appetite

As bronchiolitis progresses, it affects the lower airways, causing symptoms^[13] not normally seen in a cold:

• Persistent coughing
• Wheezing (a whistling noise when the child breathes out), which can last for a week or more
• Shallow or rapid breathing (tachypnea)
• Difficulty eating or drinking
• Bluish color in the skin (cyanosis) due to lack of oxygen (this symptom requires emergency treatment)

Call your child's healthcare provider if they show any of the signs or symptoms of bronchiolitis. If your child’s symptoms are mild, continue to monitor them in case they worsen. It’s especially important to check whether your child has bronchiolitis if they are younger than 12 weeks old or have other risk factors, such as premature birth or a heart or lung condition. Take your child to the hospital if they show these serious signs and symptoms^[14]:

• Retractions: The skin around your child’s ribs or at the base of their throat sucks in when they try to inhale.
• Pauses in breathing (apnea): Premature infants and infants within the first two months of life are more likely to have apnea. Pay special attention to your child’s breathing if they are asleep.
• Nasal flaring: If your child’s nostrils enlarge while breathing in, this may indicate that their airways are obstructed.
• Difficulty eating or drinking: Refusal to drink enough or breathing too fast to eat or drink are often cause for concern.
• Skin turning blue (cyanosis): Caused by low oxygen levels, cyanosis may first be noticed in the lips, fingers, fingernails, ear lobes, nose, or tongue.
• Sluggish or lethargic appearance

In severe cases of bronchiolitis, a child may be unable to breathe independently. These cases may require a breathing tube to be inserted into the child’s trachea to help with breathing until the infection is no longer present. If your child was born prematurely, has a lung or heart condition, or has a weakened immune system, they are more likely to get bronchiolitis. In these instances, the infection can quickly become severe and require urgent medical attention. You should take your child to his or her provider if you are unsure whether symptoms are severe. While a child with bronchiolitis will first exhibit the symptoms of a common cold, these symptoms can occasionally worsen very quickly. Your child’s provider is often the best source of information for questions and concerns related to your child’s symptoms. A provider can determine if your child’s bronchiolitis is severe or if there is a risk for complications, such as ear infection. What’s more, your provider can determine whether a condition other than bronchiolitis is causing your child’s symptoms.

Bronchiolitis virus

In most cases, bronchiolitis is caused by a viral infection. Viruses can be spread through person-to-person transmission. This occurs when a virus enters the body through the mouth, eyes, or nose. You can catch viruses like RSV from particles in the air left behind by an infected person’s cough or sneeze or by droplets left on surfaces touched by people carrying the infection. To prevent your child from catching the viruses that cause bronchiolitis, make sure you and your child wash your hands often and correctly. You should wash your hands thoroughly before touching or feeding your child, especially if you are ill. Wearing a face mask can also prevent the spread of viruses. Keep your child home if they have bronchiolitis. They should be kept away from others who are more likely to get respiratory infections (including those with heart or lung diseases and weakened immune systems). Other ways to help prevent bronchiolitis^[15] include:

• Avoid contact with people who have a cold or fever
• Clean and disinfect surfaces, especially if a family member is sick. Pay particular attention to objects that people often touch, such as doorknobs and toys.
• Wash your hands often, and teach your children about the importance of hand-washing. If soap and hot water are not available, use an alcohol-based sanitizer.
• Avoid secondhand smoke, which can also cause other respiratory illnesses.
• Breastfeeding your child can lower their chances of getting respiratory infections.
• Cover coughs and sneezes
• Use your own drinking or dining utensils

Bronchiolitis vs. bronchitis

Bronchiolitis vs. bronchitis^[16]: What’s the difference? The two are easy to confuse. Their names sound similar because they affect similar structures in the lungs. However, the conditions themselves are not related.

Bronchitis: an inflammation of the bronchial tubes

Bronchitis, unlike bronchiolitis, is an illness that affects the airways that branch off from your windpipe into your lungs (bronchi). The bronchi are responsible for producing mucus that traps dust and dirt, preventing it from reaching the lungs. Certain respiratory infections can cause the bronchi to produce excess mucus, which leads to a persistent, wet cough. Bronchitis is more likely to be seen in teens and adults than young children and infants. There are two classifications of bronchitis:

• Acute bronchitis^[17], also called a chest cold, is usually caused by a virus (such as RSV). Acute bronchitis usually improves within 7–10 days without lasting effects.
• Chronic bronchitis occurs when the bronchial tube linings are irritated or inflamed for long periods of time, often due to smoking. Air pollution, dust, or toxic fumes in a home or work environment can also contribute to chronic bronchitis. Because it is not caused by an infectious virus, chronic bronchitis is less likely to be contagious than acute bronchitis.

Bronchiolitis: a specific kind of lung infection

Bronchiolitis, by comparison, is a lung infection that affects the bronchioles (the narrower airways that branch off from the bronchi). Unlike bronchitis, bronchiolitis almost always affects children and is most common in babies who are less than one year old.