ABSTRACT
There are various viruses, both known and unknown, that target
the respiratory tract, causing infection of the upper and lower
tracts in infants and young children. Such victims will experience
6-10 infections per year, and approximately one-third will develop
a lower respiratory infection in the first year of their lives.
The majority of these infections do not require hospitalization.
Although adolescents and adults suffer from two to four respiratory
viral infections per year, these viruses are an important cause
of severe, lower respiratory tract disease in the elderly and
immunocompromised populations. All told, they cause significant
morbidity, mortality, and economic loss. In addition, since these viral
pathogens cause very similar clinical symptoms, usually defined
as “flu-like,” it is difficult to establish a clinical diagnostic that
differentiates one virus from the next. Therefore, the realization that
a new, unknown pathogen is the cause of a given outbreak typically
occurs after all known pathogens have been ruled out.1-3
