Acute lower respiratory infections are a leading cause of sickness and mortality both in children and adults worldwide. Unfortunately, acute lower respiratory infections are not uniformly defined and this may hamper a true appreciation of their epidemiological importance. From an epidemiological point of view, the definition of acute lower respiratory infections usually includes acute bronchitis and bronchiolitis, influenza and pneumonia.

Acute bronchitis can be defined as an acute illness that occurs in a patient without chronic lung disease. Symptoms include cough (productive or otherwise) and other symptoms or clinical signs that suggest lower respiratory tract infection with no alternative explanation (e.g. sinusitis or asthma).

Bronchiolitis is the most common lower respiratory tract infection and the most common cause of admission to hospital in the first 12 months of life (see chapter 16).


The incidence of acute bronchitis in adults is high, between 30 and 50 per 1000 people per year. This means that in Europe, approximately 16 500 000 adult cases are seen each year in primary care. The clinical syndrome lasts approximately 2 weeks and has a clear impact on daily activities.

Age-standardised admission rates for acute bronchitis and bronchiolitis in Europe are shown in figure 1.

Causes and pathogenesis

Identifying causative pathogens for acute bronchitis is quite difficult and most clinical studies report identification in less than 30% of cases. Almost 90% of cases are related to viruses – such as adenovirus, coronavirus, parainfluenza, influenza and rhinovirus – and less than 10% to bacteria, such as Bordetella pertussis, Chlamydophila pneumoniae and Mycoplasma pneumoniae.

Respiratory syncytial virus (RSV) is the most common cause of severe acute respiratory infection (i.e. bronchiolitis) in children (see chapter 16). Despite the generation of RSV-specific adaptive immune responses, RSV infection does not confer protective immunity in humans and recurrent infections are common.

Clinical manifestations and consequences

Acute bronchitis is a self-limiting infection in most cases, with symptoms typically lasting about 2 weeks.

RSV bronchiolitis is usually mild and self-limiting; however, some children experience more severe illness and require hospital admission, and some will need ventilatory support. Differences in innate immune function in response to the respiratory virus, as well as differences in the geometry of the airways, may explain some of the variability in clinical pattern (see chapter 16).


European Respiratory Society (ERS)/European Society of Clinical Microbiology and Infectious Diseases (ESCMID) guidelines indicate that cough suppressants, expectorants, mucolytics, antihistamines, inhaled corticosteroids and bronchodilators should not be prescribed in acute bronchitis in primary care.

Antibiotics are not usually indicated for the treatment of acute bronchitis, especially in younger patients in whom bacterial infection is not suspected (see chapter 16).

See the entire Acute lower respiratory infections Chapter