Cell-mediated immunity and part by also humoral immunity diminish in old age. Possible long-term diseases and age-related physiological changes as well as immunosuppressive medications all impair defence mechanisms and make the diagnostics more difficult. Typical symptoms of infections are often lacking or they are non-specific (e.g. difficulty in walking, confusion). Even mild infections may cause decompensation of different organs.Attention should always be paid if a stable condition in an elderly person turns strange in some way, even if there is no deterioration of the general condition nor confusion. Fever is often absent. CRP is a useful marker of infection.