Viral respiratory infection and the link to asthma.

BACKGROUND: Acute wheezing secondary to viral infection is common in children. Whereas many children suffer primarily mild to moderate symptoms, others develop severe coughing and wheezing.
METHODS: Review of recent medical literature regarding the correlation between viral illness and increased susceptibility to develop severe respiratory illnesses and subsequent asthma. DISCUSSION: In infants factors that predispose to severe disease and lower respiratory airway effects include small lung size, passive smoke exposure, virus-induced immune responses, severe disease and infection at a young age. Acute asthma symptoms have been correlated with a variety of viral pathogens, most commonly respiratory syncytial virus bronchiolitis in infancy and rhinovirus in older children. Epidemiologic and biologic factors that influence development of asthma include repeated exposure to infectious disease during early childhood, early exposure to pets, a farming lifestyle, alterations in bacterial flora of the intestine and increased use of antibiotics. Thus the likelihood of asthma is related to the specific pathogen, severity of infection, cumulative number of infections and stage of immunologic development. Progress is also being made in understanding how viruses can adversely affect lung or immune development. In asthmatic children viral infections initiate bronchospasm and airway obstruction. It is hoped that research on virus-induced airway alterations and the host factors that lead to severe clinical illnesses can help clinicians to identify children whose wheezing is an early sign of asthma.