| Haemophilus influenza (formerly called Pfeiffer's | | | | the encapsulated group. |
| bacillus or Bacillus influenza) type b (Hib) bacterium | | | | Although the unencapsulated strains are less invasive, |
| was the major cause of bacterial meningitis before | | | | they produce an inflammatory response in humans |
| the 1990s. But with the new Hib vaccines that are | | | | which can lead to many symptoms, such as mucosal |
| made available as part of the routine childhood | | | | infections while those invasive encapsulated strains |
| immunization schedule, the number of cases of this | | | | can affect many organs and cause diseases such as |
| type of meningitis have been greatly reduced. | | | | meningitis, septic arthritis and cellulitis. |
| However, when it occurs, it tends to be accompanied | | | | According to Sherris Medical Microbiology (4th |
| by an upper respiratory infection, sinusitis or ear | | | | edition), Hib infection can be effectively prevented |
| infection (otitis media). | | | | with the Hib conjugate vaccine. There are several |
| In 1930, two major types of Haemophilus influenza | | | | vaccines available for routine use against Hib. |
| were defined, which are the un-encapsulated strains | | | | However, vaccines against un-encapsulated strains |
| and the encapsulated strains. Encapsulated strains | | | | (also termed as nontypable NTHi) are not yet |
| were identified based on their distinct capsular | | | | available. |
| antigens. There are six generally recognized types of | | | | Depending on the cause of the infection, it can either |
| encapsulated Haemophilus influenzae, which are, a, b, | | | | resolve by itself within a few weeks, or it can turn |
| c, d, e, and f. Genetic diversity among | | | | into a life-threatening situation, such as a potentially |
| unencapsulated strains is much greater than within | | | | deadly brain infection in young children. |