ABSTRACT
Probably the most profound effect of immunosenescence in old age is the increase in infectious morbidity and mortality. The impact of a number of infections increase with age, including influenza, pneumonia, Clostridium difficile diarrhea, nosocomial infections, and recrudescent latent infections such as herpes zoster (1). Unfortunately, the use and abuse of antimicrobial agents selects for subsequent resistant and often unusual microorganisms that may spread from the primary source patient. This is particularly true for methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus pneumoniae. The latter is becoming increasingly resistant to standard antimicrobial therapy, is a leading cause of morbidity and mortality, and stands out among resistant organisms in that the most important of the pathogenic strains are vaccine preventable. Immunosenescence also results in atypical presentations of infections in old age, potentially obscuring the diagnoses of influenza and pneumococcal pneumonia (2). Infections also occur more frequently and are longer in duration in elderly people (3).
