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Types of Haemophilus influenzae Infections

H. influenzae most often cause pneumonia, a lung infection, but can also cause severe illnesses like meningitis (an infection of the covering of the brain and spinal cord) and bloodstream infections. Before we had a Hib vaccine, Hib was the number one cause of bacterial meningitis in children younger than 5 years old.

H. influenzae, including Hib, can cause many different kinds of infections. These infections can range from mild ear infections to severe diseases, like bloodstream infections.

When the bacteria invade parts of the body that are normally free from germs, like spinal fluid or blood, this is known as "invasive disease." Invasive disease is usually severe and can sometimes result in death.

The most common types of invasive disease caused by H. influenzae are:

  • Pneumonia* (lung infection)
  • Bacteremia (blood infection)
  • Meningitis (infection of the covering of the brain and spinal cord)
  • Epiglotittis (swelling of the windpipe that can cause breathing trouble)
  • Cellulitis (skin infection)
  • Infectious arthritis (inflammation of the joint)

H. influenzae can also be a common cause of ear infections in children and bronchitis in adults. Learn more about these respiratory illnesses.

Most Common Types of Severe Haemophilus influenzae Disease, 1999-2008.


*Pneumonia is considered invasive when H. influenzae also infects the blood or pleural fluid (fluid surrounding the lungs).

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