Viral infections.

Viral infections may cause serious morbidity as well as death in elderly patients. Of the RNA viruses, influenza virus is the most important pathogen; the majority of influenza-related deaths occur in older patients. Respiratory syncytial virus appears to be gaining increasing importance in elderly persons. Herpes zoster or shingles is caused by the DNA virus, varicella-zoster virus, and its major morbidity in older patients is postherpetic neuralgia.