Introduction.

Influenza-like illness results in greater health care costs and contributes to more deaths than any other viral illness in the United States. In recent years, the combination of influenza and pneumonia was the fifth leading cause of death in adults 65 years of age and older. In epidemic years, influenza can result in more than 100,000 hospitalizations, approximately 20,000 to 40,000 deaths, and estimated medical care costs in excess of $750 million. (1) Infection attack rates are usually highest among schoolchildren, and the age groups affected evolve to include adults and institutionalized individuals during the course of an epidemic.

It was only approximately 70 years ago that the influenza A and B viruses were first isolated in the laboratory. In a variety of studies conducted since that time, these pathogens have demonstrated a remarkable degree of adaptability, achieved largely through antigenic variation in their surface glycoproteins (hemagglutinin and neuraminidase), a phenomenon that has contributed to their long-term success. Shorebirds and waterfowl seem to serve as reservoirs for influenza, and the virus can be transmitted through various mechanisms to other birds such as chickens and turkeys, as well as to mammalian species, including horses and pigs. In fact, pigs have been shown to function as an intermediate host (ie, a "mixing vessel") in which mammalian and avian influenza strains are blended, and the resulting reassorted viruses may be pathogenic in humans. In a somewhat alarming development, during the past 6 years, influenza A has jumped the species barrier, with infection passing directly from poultry to humans, as exemplified by the 1997 experience in Hong Kong with influenza A H5N 1, and more recently in the Netherlands with influenza A H7N7. (2) In these instances, the large-scale slaughter of poultry has been performed as a control measure.

In light of the significant outbreaks of influenza that occur on nearly a yearly basis and the substantial increase in influenza-related deaths in the United States during the past 2 decades, particularly among the elderly, it is critical to optimize the use of influenza vaccine. Influenza vaccine has been shown to be highly effective in reducing the number of cases of influenza as well as the number of hospitalizations and deaths as a result of influenza. Unfortunately, in 2001, the rate of vaccination against influenza was only 63% among Americans 65 years of age or older. Nichol et al (3) recently described an added incentive for expanding the use of influenza vaccine. They showed that in an elderly population, vaccination against influenza can be associated with reduced risk of hospitalization for heart disease, cerebrovascular disease, and pneumonia or influenza, as well as reduced risk of death as a result of all causes during influenza seasons.

A credible and convincing body of evidence supporting the offering of influenza vaccine to particular groups of individuals has emerged over the years, and it is imperative that clinicians improve on their current track record. Furthermore, with regard to disease prevention, it is essential that physicians and other health care professionals who work in long-term care facilities know how to recognize and respond to an outbreak of influenza among individuals in an institutional setting. Staff who are responsible for the care of people in such settings must be familiar with appropriate diagnostic and infection control measures as well as with the proper use of vaccine and chemoprophylactic agents when an outbreak of influenza is suspected or documented.

In the articles that follow, my colleagues and I address issues pertaining to influenza, ranging from historical aspects to recommendations regarding the appropriate use of vaccines and various chemoprophylactic agents. Although there are many interesting concepts pertaining to the survival of the species (ie, antigenic variation), the occurrence of resistance to certain antiviral agents, and the role of animal reservoirs in the epidemiology of influenza infection, the most important message for practicing clinicians is that influenza vaccine is the most important tool available for preventing morbidity and mortality associated with influenza in the elderly and that the use of vaccine in this population must be improved.

References

(1.) Gravenstein S, Davidson HE. Current strategies for management of influenza in the elderly population. Clin Infect Dis 2002;35:729-737.

(2.) van Kolfschooten F. Dutch veterinarian becomes first victim of avian influenza. Lancet 2003;361:1444.

(3.) Nichol KL, Nordin J, Mullooly J, et al. Influenza vaccination and reduction in hospitalizations for cardiac disease and stroke among the elderly. N Engl J Med 2003;348:1322-1332.

From the James H. Quillen VA Medical Center and the Department of Internal Medicine, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN.

No financial support was obtained for this manuscript. The authors of this manuscript do not have any financial, commercial, or proprietary interest in any drug, device, or equipment mentioned in this article. The views contained in this article do not necessarily reflect those of the Department of Veterans Affairs of the United States.

Reprint requests to Felix A. Sarubbi, MD, Department of Internal Medicine, James H. Quillen College of Medicine, East Tennessee State University, Box 70622, Johnson City, TN 37614. Email: [e-mail]

Accepted June 19, 2003.