Viral respiratory infections in the community: epidemiology, agents, and interventions.

Viral respiratory infections are a leading cause of acute morbidity in the community. The annual frequency of respiratory illness rises during the second year of life, falls during subsequent years, increases again during child-bearing years, then decreases with advancing age (although some increase may be seen in the elderly). In terms of restriction on activity and prompting of visits to physicians, the greatest number of illnesses are associated with rhinoviruses followed by influenza viruses. However, comparing rhinovirus and influenza, there is no doubt that influenza viruses produce more severe symptoms. In some years, when there is a major influenza outbreak, they may even be identified at greater frequency. Moreover, unlike with other viruses, severity of influenza infection is high at all ages, but especially in older individuals. Influenza vaccine, which has been available for half a century, has proved effective in preventing hospitalizations for pneumonia and influenza during outbreaks of influenza types A and B. The antiviral agents amantadine and rimantadine provide approximately equivalent, and significant, efficacy in protection against clinical illness resulting from influenza type A only. However, the potential for side effects is more marked with amantadine. Some studies have shown that the rate of treatment withdrawal is no greater with rimantadine than with placebo. As we enter the next century, we may well see improvements in influenza vaccines, as well as the advent of antiviral agents that are effective against both type A and type B influenza.