What is the global 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

Current Northern European experience with Hib meningitis resembles that of North America, as does that of most industrialized nations that have had the resources to devote to immunization programs. Some data suggest, however, that in the prevaccine era, the incidence of Hib meningitis was lower in some parts of Europe than in the United States. As compared to 60-100 cases per 100,000 per year in children younger than 5 years in the United States, Finland reported 26-43 cases per 100,000 children of the same age group, as did most other Northern European countries.

Some of this variation may have been due to differences in methods of assessment (ie, voluntary reporting versus active centralized surveillance). However, to some degree, this variation may be due to genetic factors, ecological niches in which certain predisposing viruses maintain a local annual presence, regional early childhood experiences pertinent to immune system function, or other unknown influences.

Some authorities have proposed that the variation occurs because more Northern European mothers breastfeed their infants and that they tend to do so for longer periods than North American mothers, thereby prolonging the period of protection afforded by passively transmitted antibodies.

Annual incidence of Hib meningitis in children younger than 5 years in various years have been reported as 9 cases per 100,000 in Austria, 6 cases per 100,000 in Spain, [3] 8 cases per 100,000 in Romania, [4] and 8 cases per 100,000 in Greece. Interestingly, the Romanian data show a very high rate for meningococcal meningitis (22 cases per 100,000 per year for children younger than 5 years. [4] ) At the time of publication of the Romanian data, no immunization program was in place for Hib.

The annual incidence for Hib meningitis in Western Australia in the preimmunization era was reported as 150 cases per 100,000 children younger than 5 years. [5] This high incidence may reflect increased vulnerability among the regionally prevalent indigenous peoples of Australia. Striking improvement in this incidence was observed after institution of immunization.

Unfortunately, in many areas of the world, Hib meningitis continues to be the enormous threat to public health that it once was in the United States and Northern Europe. The incidence remains high in developing countries—including many or perhaps most tropical and many Asian nations and those currently experiencing the disruption produced by warfare—where lack of resources has resulted in the virtual absence or delayed initiation of anti-Hib vaccination programs.

Establishing the exact degree of risk has been difficult because in many countries, inadequate resources have been devoted to establishing the epidemiology of Hib diseases. Nevertheless, researchers have calculated rates of more than 50 cases per 100,000 per year in Ghana and Uganda. [6] Internationally, the spectrum of serious Hib illnesses, including meningitis, may account for as many as 1.9 million deaths per year in children younger than 5 years. [7]

On the other hand, some Middle Eastern and Asian nations have recently reported low rates of Hib meningitis in children younger than 5 years, such as 3.8 cases per 100,000 in Thailand, [8] 6 cases per 100,000 in South Korea, and 1-10 cases per 100,000 (varying by region) in China. [9] Curiously, the survey of bacterial meningitis among young children in Guangxi, China by Dong et al found a much higher incidence of staphylococcal meningitis than of Hib meningitis. In Japan, the annual incidence of Hib has significantly decreased in the last decade from 0.66 to 0.01. [10]

Annual incidences of less than 15 cases per 100,000 per year in children younger than 5 years have been recently reported for Iran, Jordan, and Uzbekistan. The annual incidence of Hib meningitis in Saudi Arabia has been estimated to be 17 cases per 100,000 per year in children younger than 5 years. [11]

The reports showing low rates of Hib meningitis in Asia stand in contrast to data from other Southeast Asian locations demonstrating much higher annual incidence, such as 2 studies in the Philippines showing an annual incidence of 18-95 cases per 100,000 per year in children younger than 5 years. [12, 13]

To some extent, the high variability from country to country may reflect disparities in data-gathering methodology. However, the data of Rerks-Ngarm et al from Thailand [8] appear to have been diligently and carefully obtained, although questions have been raised about possible methodological flaws. [7]

Thus, data on the incidence of meningitis and other serious Hib illnesses among children younger than 5 years in Southeast Asia and various other tropical regions remain controversial, particularly where the incidence of these diseases appears low even in the absence of immunization. The problem of interpreting results of blood and CSF cultures in the large number of children who have previously received antibiotics has been particularly significant, as has the problem of knowing how carefully all avenues of healthcare-seeking by the local population have been investigated.

Particularly heartening is the report that 14 years after the introduction of Hib vaccination in Gambia, the annual incidence remains below 5 cases per 100,000 children. [14, 15] Given the incomplete coverage achieved by Gambian children (estimated to be less than 70%), this result is strongly supportive of the concept of herd immunity as an important determinant of risk. Moreover, this effect was achieved with either 2 or 3 vaccinations for children who received vaccine.

Similarly positive information has been reported for Hib vaccination programs instituted in Chile and the Dominican Republic, where, before immunization, the annual incidence of Hib meningitis in children younger than 5 years had been higher than 20 cases per 100,000.

Significant declines in incidence of Hib meningitis are reported for hospitals in Argentina and South Africa, as well as declines in percentage of positive CSF indicators of bacterial meningitis, such as elevated white blood cell count, low glucose, elevated protein, or turbidity. These are possible surrogate markers for assessment of efficacy of Hib immunization in developing countries. [16]


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