Chapter 22 Influenza and Other Viral Respiratory Tract Infections

1. Clinical manifestations of viral respiratory infections are nonspecific 2. Diagnostic procedures should be pursued if a viral infection is considered, particularly among immunocompromised hosts. 3. Vaccination, when available, is the most effective method of avoiding respiratory viral infections. 4. Resistance to existing antiviral therapy is on the rise and resistance patterns should be considered before an antiviral is prescribed. 5. Preemptive therapy is important for preventing opportunistic viral infections in immunocompromised hosts. V iruses are important causes of community-acquired pneumonia inchildren and adults (Table 22-1). Although influenza and respiratorysyncytial viruses (RSVs) are the most common causes of serious viral respiratory illness; parainfluenza, adenoviruses, and other agents are also significant pathogens (1). In adults, severe viral pneumonia is more fre-quent in elderly patients, persons with chronic lung disease such as chronic obstructive pulmonary disease (COPD), and other chronic medical illnesses and immunosuppressive conditions. The true proportion of community-acquired pneumonia in adults caused by viruses is difficult to determine because of the limited testing for viral pathogens in many settings and the limited sensitivity of some diagnostic tests. However, viral infections have been identified in approximately 10% (range 4 % to 39%) of relatively immunocompetent adults hospitalized with community-acquired pneumonia (2). In a recent well-done prospective study Tan ch22.qxd 10/12/07 5:26 PM Page 417 from the United Kingdom, of 267 adults with community-acquired pneumo-nia, viruses were suspected to be the cause of pneumonia in 23 % (3). The frequency of reported viral pneumonias has increased during the past decade, most likely caused by a combination of better diagnostic tech-niques and an increasing risk for viral pneumonias among the growing immunocompromised population. This chapter will focus on modern diag-nostic techniques and the most frequent viral pathogens causing severe lower respiratory disease in adults. The clinical and public health chal-lenges imposed by new respiratory pathogens such as avian influenza, severe acute respiratory syndrome (SARS), and human metapneumovirus will also be discussed