A fever and symptoms that affect the brain and nervous system may mean a serious infection is present. Symptoms include:

• Severe headache with a stiff neck.
• Mental changes, such as confusion, increased fussiness, or decreased alertness (lethargy).
• Shaking chills.
• Severe eye sensitivity to light (photophobia).

The flu, which usually is not serious, can cause a high fever. You usually will also have body aches, rather than other, more serious, symptoms.

If a serious infection is present, other symptoms in addition to fever usually are present or will develop quickly. Any fever with signs of a serious infection needs to be evaluated immediately by a health professional.