Hib bacteria usually live harmlessly in the nose and throat, but they can move to other parts of the body and cause different kinds of illnesses, all known as H. influenzae disease.
There are six types of H. influenzae bacteria, labeled a through f. Most people only need to worry about type b. It can cause these serious illnesses:
- Meningitis An infection of the brain and spinal cord membranes may lead to brain damage, hearing loss, or even death. Prior to the Hib vaccine, infection with Hib bacteria was the leading cause of bacterial meningitis in children under 5 years old in the United States.
- Pneumonia A severe lung infection can make breathing difficult and cause long-term health problems.
- Epiglottitis An infection causes swelling of the epiglottis, the small flap in the throat, potentially blocking the airway and leading to difficulty breathing.
- Bloodstream Infections These can result in sepsis, a life-threatening condition in which the body’s excessive response to infection causes injury to organs.
- Cellulitis A deep skin infection causes painful swelling.
- Infectious Arthritis Also called septic arthritis, this is a painful infection of the joint.
Anyone can get H. influenzae, but serious cases, including Hib, mostly happen in children younger than 5 and adults 65 or older. Children under 1 have the highest rates of infection.
Although experts don’t know why, Black, Alaska Native, and Native American children have increased rates of serious disease.
Hib spreads through respiratory droplets when an infected person coughs or sneezes, or through close contact with respiratory secretions. People who aren’t sick but have the bacteria in their nose and throat can still pass the bacteria to others; that’s how H. influenzae spreads in most cases. It can also spread to people who have close and prolonged contact with a person who has H. influenzae disease.