The most common causes of meningitis are bacterial infections that start in other parts of the body and spread to the brain or spinal cord via the bloodstream. Meningitis can also also caused by viruses, chemical irritation, or tumors.

Acute bacterial meningitis, which can be caused by gram-negative bacteria, is very serious and should be treated immediately to prevent permanent damage. Bacteria causing gram-negative meningitis include Pseudomonas aeruginosa, Escherichia coli, Enterobacter aerogenes, Proteus morganii, and Klebsiella pneumoniae.

Risk factors include recent brain surgery and recent trauma or injury to the head. The infection is sometimes associated with spinal fluid shunt placement after brain surgery. Spinal abnormalities, urinary tract abnormalities, a local infection, or urinary tract infection may be predispose children to this type of meningitis.

Gram-negative meningitis is much more common in infants than adults.

• Fever
• Severe headache
• Nausea and vomiting
• Stiff neck
• Sensitivity to light (photophobia)
• Mental status changes
• Symptoms suggesting infection of bladder or kidney, intestines, or lung that might be the source of the spinal fluid infection

• Low blood pressure
• Fast heart rate
• Stiff neck
• Elevated white blood cell count in blood
• Spinal fluid showing increased white blood cells, low glucose, high protein
• Special stain of the spinal fluid showing white blood cells and sometimes gram-negative bacteria
• CSF culture growing gram-negative bacteria
• Blood culture growing gram-negative bacteria
• CT scan of the brain (usually normal)

• Shock with damage to other organs
• Brain abscess (collection of bacteria in the brain itself)
• Brain damage