[Respiratory tract viruses].

The respiratory tract is the site of entrance of many viruses. However, not all of them cause symptomatic respiratory infections. In the past the clinical significance of some viruses was underestimated. Viruses leading to population-wide epidemics like influenzavirus or to nosocomial outbreaks like respiratory syncytial virus or SARS-associated coronavirus have a great impact on public health and the respective preventive measures are of paramount importance. The advent of new diagnostic tools led to discoveries and additional information about some "banal" viruses causing severe diseases in special hosts such as infants and immunosuppressed patients. In addition new viral pathogens were discovered and found to cause respiratory infections, metapneumovirus and SARS-associated coronavirus being the most important ones.