Haemophilus influenzae meningitis is an infection of the membranes covering the brain and spinal cord (meninges) caused by H. influenzae bacteria.

Haemophilus influenzae type B (Hib) is a type of bacteria, not to be confused with the disease influenza, an upper respiratory infection caused by the influenza virus.

Prior to the availability of the Hib vaccine, H. influenzae was the leading cause of bacterial meningitis in children under 5 years of age.It occurred most frequently in children from 1 month up to 4 years, with a peak at 6 to 9 months. Since the introduction of the vaccine in the U.S., H. influenzae now occurs in less than 2 in 100,000 children. It still causes between 5% - 10% of bacterial meningitis cases in adults.

H. influenzae meningitis may follow an upper respiratory infection, and may develop slowly or quickly. The infection usually spreads from the respiratory tract to the bloodstream, and then to the meninges. At the meninges, the bacteria produce infection and inflammation, causing serious illness and sometimes death.

Risk factors include a recent history of otitis media (ear infection), sinusitis (infection of sinuses), pharyngitis (sore throat), other upper respiratory infection, or a history of a family member with an H. influenzae infection. Another significant risk factor is race -- Native Americans have a rate of more than 3 times that of the general population. Placement in day care also increases risk.

• Irritability, poor feeding in infants
• Fever (in young infants the temperature may actually be below normal)
• Severe headache (older children)
• Nausea and vomiting
• Stiff neck or pain in neck when flexed
• Pain in back when neck is flexed forward and chin brought toward chest (older children)
• Unusual body positions
• Sensitivity to light

For any patient with meningitis, it is important to perform a lumbar puncture (spinal tap), where a spinal fluid (known as cerebrospinal fluid, or CSF) is collected for testing.

Other signs and tests include:

• Bulging of the fontanelles (the soft spots on an infant's head)
• Opisthotonos (lying with the back arched, head, back, and chin up)
• Seizures
• Poor circulation(blood flow through the body)
• Mental status changes (such as irritability, reduced consciousness, coma)
• High white blood cell count in blood
• Spinal fluid showing increased number of white blood cells
• Spinal fluid culture showing bacteria
• Serology (antibodies in blood) showing recent exposure to H. influenzae
• Blood culture growing H. influenzae