What is the prevalence of Haemophilus influenzae type b (Hib) meningitis in the US?

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

In the prevaccine era, the annual rate of Hib meningitis in the United States varied considerably. Some well-defined regions exhibited year-to-year variations of as much as 67%. Considerable additional variation was observed in comparisons among regions; higher rates were observed in certain regions (eg, Alaska). This variation was presumably due to year-to-year changes in the virulence or invasiveness of prevalent meningitis-associated Hib strains. Far less evidence exists in favor of Hib meningitis epidemics than has been found for Neisseria meningitidis meningitis.

In the United States, before effective vaccination, Hib accounted for 40-60% of all cases of meningitis in children aged 0.1-15 years and fully 90% of all cases of meningitis arising in children aged 0.1-5 years. Hib meningitis was rare in individuals older than 5 years. However, because it was the chief cause of meningitis in children younger than 5 years and because the incidence of meningitis is much higher in this age group than in any other, Hib was the cause of nearly half of the approximately 25,000 cases of meningitis occurring annually in patients of any age.

In the prevaccine era, the incidence of serious Hib disease was 60-100 cases per 100,000 children younger than 5 years in the United States. To some extent, this may reflect the inclusion of populations at higher risk for Hib meningitis (eg, Eskimos, Apaches, and Navajos). The use of effective conjugated vaccines has dramatically reduced the risk of Hib meningitis in young children, lowering the annual incidence in well-immunized populations by 76-90%.

With opportunity, Hib colonization is readily achieved in small children. In prevaccine-era studies of households containing a child who developed Hib meningitis, as many as 20-25% of family contacts and more than 50% of siblings younger than 10 years developed encapsulated Hib carriage. Among exposed contacts, the rate of disease is 4% for children younger than 2 years, 2-3% for children aged 2-3 years, and 0.1% for children aged 4-5 years. Thus, the risk for disease is about 600-fold greater than the age-adjusted risk for the population at large.


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