Haemophilus influenzae (Hib) is an infection caused by bacteria. The most common type of invasive Hib disease is meningitis, an infection of the membranes that cover the brain and spinal cord. It usually affects children under the age of five. The bacteria are spread from person to person. Some people carry Hib bacteria in their nose and do not become infected. They can, however, pass the bacteria to others who may become sick. Symptoms may include fever, decreased mental status, and stiff neck. Hib can be treated with antibiotics. The disease can be prevented through vaccination.