Viral respiratory tract infections are the most common cause of symptomatic human disease among children and adults. They account for more time lost from school and work than any other infection. These infections may cause a wide variety of diseases, from the common cold to severe pneumonia, and may result in death. Pneumonia is an infection or inflammation of the lungs. It can be in just one part of the lungs, or it can involve many parts. Bacteria, viruses, fungi, and other microorganisms cause pneumonia. The severity of pneumonia depends on which organism is causing the infection. Viral pneumonia is an inflammation of the lungs caused by infection with a virus. Viral pneumonia is a subset of the pneumonitides, which were at one time called atypical pneumonias (Hull, 1989). Viral pneumonias are usually not very serious, but they can be life threatening.
The incidence of viral pneumonia has increased during the past decade. The increase primarily is because of improved diagnostic techniques and the growing population of patients who are immunocompromised (Dreher, 1997). In the past, the diagnosis of viral pneumonia was made essentially on clinical grounds. All pneumonias were labeled atypical if a bacterial pathogen could not be identified with Gram staining and if the pneumonia did not respond to antibiotics. With the advent of cell culture techniques, though, it became possible to establish a viral etiology in some cases. Over the past 10 years, new biotechnology has greatly facilitated the diagnosis of viral pneumonias. Clinicians are able to obtain a virologic diagnosis with a high degree of sensitivity and specificity, often within a few hours of the diagnostic procedure. Furthermore, improved approaches to prevention and treatment of viral pneumonias have also become available. .
Viruses are divided into categories depending on whether the pneumonia they cause is a primary manifestation or part of a multi-system syndrome of disease.