Respiratory Viral Infections

Respiratory viral infections are associated with a huge societal burden—both medical and economic. The incidence and impact of these viral infections tend to be greatest at the extremes of life; in infancy and in the elderly. Respiratory viruses frequently cause lower tract disease in up to 70% of respiratory illness in children and 20 to 30% in adults and may often be the sole pathogen identified. They are also increasingly recognized as a major cause of morbidity and mortality in organ or hematopoietic stem cell transplant recipients. In this issue of Seminars in Respiratory and Critical Care Medicine, an expert panel of investigators provides a series of updates on the epidemiology and worldwide burden of the recent pandemic influenza outbreak. The authors discuss the lessons learned during the pandemic outbreak, the critical care aspects of patients with severe influenza infection, and the emerging antiviral resistance of pandemic influenza. They review the role of these common respiratory viruses and the DNA viruses in adults and solid organ transplant recipients and provide updates regarding vaccine development and molecular assays for the detection of respiratory viral infections.

Several themes occur throughout the articles in this issue. Although the respiratory viruses cause direct effects of tissue injury and clinical illness, in the very young, the elderly, or immunosuppressed transplant populations they may be life threatening and produce indirect effects that may lead to long-term adverse sequelae. Community-acquired respiratory viruses such as respiratory syncytial virus, parainfluenza virus, influenza A and B, adenovirus, and rhinovirus are increasingly recognized as important pathogens not only in infants and the elderly but also in lung transplant recipients. Newly described viruses such as human metapneumovirus or emerging viruses such as West Nile virus and SARS-associated coronavirus are being reported in increasing frequency in transplant recipients. The herpesviruses, which include cytomegalovirus, Epstein-Barr virus, herpes simplex virus 1 and 2, varicella-zoster virus, and human herpesvirus 6, 7, and 8 have important immunomodulatory effects in addition to their direct infectious effects. Development of potent oral antiviral agents, vaccines, and very sensitive molecular techniques for the detection of viral infections, their response to therapy, and the emergence of isolates with antiviral resistance have had significant impacts on the approach to respiratory viral infections. This issue discusses the individual pathogens; the role of new molecular diagnostic techniques; the development of potent antiviral agents; treatment regimens for established viral infection; the incidence, risk factors for, and impact of antiviral resistance; and, in the transplant recipient, prevention strategies in the era of potent oral antiviral agents and the potential impact of antiviral therapy on the indirect effects of these viruses on long-term allograft function.

We hope that the readers will find this issue helpful in the management of their patients with respiratory viral infections.