- Published on
Infectious Disease and Microbiology – Bronchiolitis
Bronchiolitis is an acute inflammatory disease of the lower respiratory tract that primarily affects the terminal and respiratory bronchioles. It most commonly results from viral infection, leading to inflammatory obstruction of small airways. In some cases, inflammation may extend to adjacent alveolar ducts and alveolar spaces. Although typically viral in origin, bacterial infections can occasionally cause bronchiolitis.
Bronchiolitis is most common in infants and young children, particularly during the first two years of life, with peak incidence around 6 months of age. In the United States, the incidence has been reported as high as 11 cases per 100 children per year during the first year of life. Approximately 6 per 1,000 infants under 6 months are hospitalized annually. Each year, an estimated 675,000 ambulatory visits and 75,000 hospitalizations occur in children younger than 2 years. Bronchiolitis is the most common cause of hospitalization in infants and follows a seasonal pattern, with peak incidence during winter and early spring months.
Risk factors include male sex, age between 3 and 6 months, lack of breastfeeding, exposure to cigarette smoke, crowded living conditions, child care attendance, prematurity, low birth weight, age less than 6–12 weeks, chronic lung disease, congenital heart disease, immunodeficiency, neurological disease, congenital airway abnormalities, and high altitude. Environmental exposures such as toxic fumes, mineral dust, tobacco smoke, and certain medications (e.g., penicillamine) have also been implicated. Bone marrow, lung, and heart–lung transplantation have been associated with bronchiolitis as well.
The pathophysiology involves viral penetration of bronchiolar epithelial cells, leading to direct cellular injury and inflammation. Edema, increased mucus production, and sloughed epithelial cells obstruct small airways, resulting in air trapping and atelectasis. This obstruction contributes to wheezing, impaired gas exchange, and respiratory distress.
The most common causative agent is respiratory syncytial virus (RSV), responsible for more than 50% of cases. Other viruses include parainfluenza, influenza, rhinovirus, rubeola, mumps, parvovirus, enterovirus, coronavirus, coxsackievirus, human metapneumovirus, and varicella zoster virus. In adults, rare cases have been associated with Mycoplasma pneumoniae and Legionella pneumophila. Histologically, bronchiolitis may present as inflammatory bronchiolitis, constrictive bronchiolitis obliterans, or proliferative bronchiolitis. Otitis media is a commonly associated condition.
Clinically, bronchiolitis often begins with mild upper respiratory symptoms such as nasal congestion, coryza, and sneezing, lasting several days and sometimes accompanied by decreased appetite. Fever typically ranges between 38.5°C and 39.0°C. As the illness progresses, lower respiratory symptoms develop, including cough, expiratory wheezing, tachypnea, grunting, retractions, increased respiratory effort, and air trapping. Infants may appear in significant respiratory distress. Wheezing is common, though crackles—particularly early in inspiration—are frequently heard.
Laboratory studies are generally not diagnostic; white blood cell counts are usually normal. In severe cases, viral testing may be performed. Chest radiographs often show hyperinflation and increased anteroposterior diameter, reflecting air trapping.
The differential diagnosis includes asthma, congestive heart failure, foreign body aspiration, pertussis, organophosphate poisoning, cystic fibrosis, and bronchopneumonia. A key distinguishing feature is that bronchiolitis typically represents the first episode of wheezing in an infant, whereas asthma is characterized by recurrent wheezing.
Management is primarily supportive. Oxygen therapy, hydration, and respiratory support are the mainstays of treatment. Infants with significant respiratory distress require hospitalization and are often placed in cool, humidified oxygen. The routine use of bronchodilators is not recommended, as evidence does not support consistent clinical benefit or reduction in hospitalization. Short-term improvement in oxygen saturation or clinical scores may occur with nebulized beta-agonists in some outpatient settings, but they are not recommended for routine use. Ribavirin has been used in select high-risk patients with RSV infection, though its use remains controversial.
Most infants recover with supportive care. However, some may progress to respiratory failure requiring ventilatory support. Long-term follow-up has shown that a proportion of infants with bronchiolitis may develop hyperreactive airways later in childhood. The overall case fatality rate is less than 1%, and mortality among high-risk infants remains below 3.5%.
Bronchiolitis is an acute inflammatory disease of the lower respiratory tract that primarily affects the terminal and respiratory bronchioles. It most commonly results from viral infection, leading to inflammatory obstruction of small airways. In some cases, inflammation may extend to adjacent alveolar ducts and alveolar spaces. Although typically viral in origin, bacterial infections can occasionally cause bronchiolitis.
Bronchiolitis is most common in infants and young children, particularly during the first two years of life, with peak incidence around 6 months of age. In the United States, the incidence has been reported as high as 11 cases per 100 children per year during the first year of life. Approximately 6 per 1,000 infants under 6 months are hospitalized annually. Each year, an estimated 675,000 ambulatory visits and 75,000 hospitalizations occur in children younger than 2 years. Bronchiolitis is the most common cause of hospitalization in infants and follows a seasonal pattern, with peak incidence during winter and early spring months.
Risk factors include male sex, age between 3 and 6 months, lack of breastfeeding, exposure to cigarette smoke, crowded living conditions, child care attendance, prematurity, low birth weight, age less than 6–12 weeks, chronic lung disease, congenital heart disease, immunodeficiency, neurological disease, congenital airway abnormalities, and high altitude. Environmental exposures such as toxic fumes, mineral dust, tobacco smoke, and certain medications (e.g., penicillamine) have also been implicated. Bone marrow, lung, and heart–lung transplantation have been associated with bronchiolitis as well.
The pathophysiology involves viral penetration of bronchiolar epithelial cells, leading to direct cellular injury and inflammation. Edema, increased mucus production, and sloughed epithelial cells obstruct small airways, resulting in air trapping and atelectasis. This obstruction contributes to wheezing, impaired gas exchange, and respiratory distress.
The most common causative agent is respiratory syncytial virus (RSV), responsible for more than 50% of cases. Other viruses include parainfluenza, influenza, rhinovirus, rubeola, mumps, parvovirus, enterovirus, coronavirus, coxsackievirus, human metapneumovirus, and varicella zoster virus. In adults, rare cases have been associated with Mycoplasma pneumoniae and Legionella pneumophila. Histologically, bronchiolitis may present as inflammatory bronchiolitis, constrictive bronchiolitis obliterans, or proliferative bronchiolitis. Otitis media is a commonly associated condition.
Clinically, bronchiolitis often begins with mild upper respiratory symptoms such as nasal congestion, coryza, and sneezing, lasting several days and sometimes accompanied by decreased appetite. Fever typically ranges between 38.5°C and 39.0°C. As the illness progresses, lower respiratory symptoms develop, including cough, expiratory wheezing, tachypnea, grunting, retractions, increased respiratory effort, and air trapping. Infants may appear in significant respiratory distress. Wheezing is common, though crackles—particularly early in inspiration—are frequently heard.
Laboratory studies are generally not diagnostic; white blood cell counts are usually normal. In severe cases, viral testing may be performed. Chest radiographs often show hyperinflation and increased anteroposterior diameter, reflecting air trapping.
The differential diagnosis includes asthma, congestive heart failure, foreign body aspiration, pertussis, organophosphate poisoning, cystic fibrosis, and bronchopneumonia. A key distinguishing feature is that bronchiolitis typically represents the first episode of wheezing in an infant, whereas asthma is characterized by recurrent wheezing.
Management is primarily supportive. Oxygen therapy, hydration, and respiratory support are the mainstays of treatment. Infants with significant respiratory distress require hospitalization and are often placed in cool, humidified oxygen. The routine use of bronchodilators is not recommended, as evidence does not support consistent clinical benefit or reduction in hospitalization. Short-term improvement in oxygen saturation or clinical scores may occur with nebulized beta-agonists in some outpatient settings, but they are not recommended for routine use. Ribavirin has been used in select high-risk patients with RSV infection, though its use remains controversial.
Most infants recover with supportive care. However, some may progress to respiratory failure requiring ventilatory support. Long-term follow-up has shown that a proportion of infants with bronchiolitis may develop hyperreactive airways later in childhood. The overall case fatality rate is less than 1%, and mortality among high-risk infants remains below 3.5%.
0 Comments
