Bronchiolitis is usually the result of viral inflammation of the very small airways (bronchioles). In affected children of less than 2 years of age it is characterised by rapid breathing, chest retraction and wheezing.
Respiratory syncytial virus (RSV) infection is the most important cause of bronchiolitis and other lower respiratory tract infections during the first year of life, and is also one of the major causes of hospital admissions in infants under 1 year of age. Affected children characteristically present with symptoms of a viral infection with mild rhinorrhoea, cough, and, on occasion, a low-grade fever. Within 1 or 2 days, these symptoms are followed by rapid respiration, chest retraction and wheezing. The infant may be irritable, feeding poorly and vomiting. Other causative viruses for bronchiolitis are human meta-pneumovirus, rhinovirus, adenovirus and influenza virus. Prevalence studies have shown that up to 50% of infants are infected by RSV by their first birthday and almost 100% by 2 years of age, with the highest prevalence during the winter. In the first year of life, the hospitalisation rate for RSV infection, i.e. bronchiolitis, has been reported to be 1–2% of all infants and 10–15% in high-risk infants. Intensive care admissions for bronchiolitis are high, as recently reported in a retrospective study in France of 467 children admitted to 24 paediatric intensive care units (PICUs); 75% were aged less than 2 months, 76% had positive RSV tests and about one-third required noninvasive and/or mechanical ventilation. Six of the infants died. More than 50% of the neonates had a predisposing condition such as prematurity, respiratory disease including bronchopulmonary dysplasia (BPD) and congenital heart disease.
Hospital admission rates for acute bronchitis and bronchiolitis combined in children less than 1 year of age vary between countries and are particularly high in the Baltic states (Lithuania and Latvia), Finland, and the UK. For most European countries, however, this information is not available (figure 2).
Mortality from bronchitis and bronchiolitis in western Europe is generally low, but in many countries in eastern Europe, mortality rates for these diseases are unexpectedly and alarmingly high, as shown in figure 3.
The development of a vaccine to prevent RSV bronchiolitis has thus far not been successful. Furthermore, it is unclear how early in life such a vaccine should be administered. It is reasonable to assume that an RSV vaccination programme would have to start before the conventional vaccination programme against common childhood infections, i.e. before the age of 2 months.
The monoclonal antibody palivizumab has been proven to reduce severe RSV infections in high-risk infants and protection appears to extend beyond the current monthly dosing. However, studies indicate that its cost-effectiveness is low. The high costs of prophylaxis with palivizumab mean it is not available in many European and low-income countries.
It is important that a reliable and highly effective vaccine and a prevention programme becomes available in the future, especially for high-risk infants. A reduction of the number of deaths due to failure of therapy in bronchiolitis, especially in eastern European countries, should be the aim of future European health programmes.