Haemophilus influenzae and Haemophilus influenzae type B (Hib)

What is Haemophilus influenzae?
Haemophilus influenzae is a bacteria that can cause serious infection in humans, particularly in children, but also in individuals with weakened immune systems.

Are there different types of Haemophilus influenzae?
There are a number of strains of H. influenzae. Strains are classified as those with capsules (capsular types) and those without capsules (non-encapsulated types). Six capsular types (a-f) are recognized. In the prevaccine era, type b was the most commonly reported strain. The non-encapsulated strains cause mucosal infection (such as middle ear infections, called "otitis media") but rarely lead to serious invasive disease.
What is Haemophilus influenzae type b?
H. influenzae type b (also known as "Hib") is just one of six H. influenzae types. Before a vaccine was available to prevent H. influenzae type b disease Hib accounted for approximately 80-95% of all strains that caused invasive illness.

What illnesses does Haemophilus influenzae cause?
Haemophilus influenzae causes a number of diseases. These are:

  • Otitis media
  • Meningitis
  • Pneumonia
  • Septicaemia
  • Epiglottitis
  • Septic arthritis
  • Cellulitis
  • Osteomyelitis

What illnesses does Hib cause?
Hib can cause the same illnesses as other types of Haemophilus influenzae - but the one of the most common and worrying presentations of Hib disease is meningitis.

How is Hib transmitted?
Hib lives in the nose and throat of humans and is transmitted from person to person through respiratory droplets, or contact with respiratory secretions. The bacteria may be carried around in the nose and throat for a short while or for several months without causing symptoms ("asymptomatic carrier"). In some individuals (particularly those most at risk) Hib will invade the body causing invasive disease (e.g. meningitis, septicaemia).

How many cases of Haemophilus influenzae occur each year in Ireland?
Between 15-40 cases of Haemophilus influenzae have been reported annually since 1996. Haemophilus influenzae disease (invasive) became a notifiable disease in 2004. 

For details on Haemophilus influenzae figures and trends please see here.

Can Hib be prevented?
Yes, Hib can be prevented with the Hib vaccine. Please see http://www.immunisation.ie for more information. Since Hib vaccine was introduced in 1992 there has been a dramatic decrease in the number of invasive Hib cases reported in Ireland.

When is Hib vaccine given to children?
Hib vaccine is offered to all children as part of the routine childhood vaccination programme in Ireland. Hib vaccine is part of the "six-in-one" vaccine and is given at 2, 4 and 6 months of age. In addition all children reaching 12 months of age are now offered a Hib booster at the same time as MMR vaccine to give extra protection against Hib infection. All children under four years of age should be fully vaccinated against Hib. If a child between the ages of 1-4 years has not been previously immunised with Hib vaccine and has presented for vaccination they only need one dose of the Hib vaccine.

Should anyone else (other than children) get the vaccine?
Hib vaccine is also recommended for individuals who are at risk of Hib infection (see "Who is most at risk of Hib infection?")

Who is most at risk of Hib infection?

  • Young children are most at risk of Hib infection, particularly those less than 4 years of age

Other individuals at risk of Hib infection are:

  • Individuals with a malfunctioning or lack of spleen, irrespective of how old they are (e.g. sickle cell disease, HIV, or other immunodeficiency)

This is a vaccine preventable disease for which there is a national immunisation programme in Ireland. See http://www.immunisation.ie for more information on Haemophilus influenzae and Hib vaccination.

Last reviewed: 28th November 2007

Health Protection Surveillance Centre, 25-27 Middle Gardiner St, Dublin 1, Ireland. t: +353 1 8765300 f: +353 1 8561299 e:hpsc@hse.ie
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