Which age groups have the highest prevalence of Haemophilus influenzae type b (Hib) meningitis?

Updated: Jul 09, 2018
  • Author: Prateek Lohia, MD, MHA; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

Virtually all studies conducted in the prevaccine era on children from North America or Northern Europe showed that the great majority of Hib meningitis cases occur within a fairly narrow age range. In 1933, Fothergill and Wright showed that children younger than 2 months accounted for less than 0.004% of all cases of Hib meningitis.

More recent studies have suggested that children younger than 2 months account for 0.3% of cases. The risk to neonates may have increased in the late 20th century because of a decrease in maternal transmission of Hib antibodies, possibly as the result of diminished maternal exposure.

In prevaccination studies, infants younger than 6 months accounted for only about 10% of Northern European Hib meningitis cases, as compared to 16-38% of North American cases. For unclear reasons, a profile similar to the North American prevalence figures was found for Australian Aborigines. The tendency toward later onset of Hib meningitis in Northern Europe may be due to more widespread and prolonged breastfeeding by Northern European mothers.

The peak Hib meningitis risk for unvaccinated North American children was from age 6-9 months, with a continued very high risk until approximately 24 months of life. Prevalence for Hib meningitis among children aged 6-17 months during the prevaccine era was approximately 122 cases per 100,000 population per year, as compared with 65 cases per 100,000 population per year for infants aged 18-23 years. After 23 months, a rapid decline in prevalence was observed.

In Northern European studies, the peak risk for Hib meningitis in unvaccinated populations occurs in older children than in North America. The mean age at presentation of Hib meningitis in Northern Europe is approximately 1.5 years of age. Although approximately 80% of North American cases occur in children prior to their second birthday, only 60% of Northern European cases occur in such young children.

Throughout the world, children younger than 1 year account for approximately 59% of all Hib meningitis cases, while another 24% of all cases occur in the second year of life. [2] Children in their first year of life have manifested incidence rates of 30-66 cases of Hib meningitis per 100,000 per year.

Risk for Hib meningitis declines rapidly after the second birthday and becomes quite low after the fourth. After age 15 years in unvaccinated populations, Hib is responsible for only 1-3% of all infectious meningitis cases.

Adults may be rendered vulnerable to Hib meningitis by chronic diseases such as alcoholism, nephrosis, diabetes mellitus, CSF fistula, asplenia, agammaglobulinemia, neoplasms (eg, chronic lymphocytic leukemia, multiple myeloma, Hodgkin disease), and AIDS, as well as by chemotherapy or radiotherapy. However, cases of Hib meningitis have occurred in adults who have no clearly identified risk factors.


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