Although elderly patients can have minor viral illnesses, just as can all other segments of the population, they are at high risk for severe infections and sepsis. Comorbid diseases such as diabetes and peripheral vascular disease can make an otherwise simple infection complicated. As noted above, many elderly patients will not have a fever in the face of significant infection. The presence of fever should thus raise the ED clinician's level of concern. She's just demented.
Many elderly patients do, in fact, suffer from chronic dementias.
All too often, clinicians assume that a rapid degradation in mental function is simply due to progression of the patient's dementia. He's just depressed. Another common mistake is to assume that depression in the elderly is the cause for mental status changes. Although this can certainly occur in severe cases, to hang one's hat on this assumption is to risk missing the diagnosis of organic disease that may be reversible or palliable. Acute onset of symptomatology mandates aggressive workup and diligent treatment.