What is the global prevalence of Haemophilus influenzae infections?

Updated: Jun 11, 2021
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Before vaccines became available, invasive Hib disease was a leading infectious illness among children worldwide. Hib vaccine is routine in the Americas, most of Europe, and a few countries in Africa and the Middle East.

In the 1990s, the frequency of Hib diseases decreased remarkably, and even developing countries reported only 2-3 cases per 100,000 of the population younger than 5 years.

In Canada, 10 centers reported 485 cases of invasive H influenzae disease in 1985. In 2000, 8 years after Canada implemented their Hib immunization program, their Immunization Monitoring Program, ACTive (IMPACT) reported only 4 cases. A report of invasive Hib disease in Canadian children identified 29 cases from 2001-2003. The number of cases progressively decreased over the 3 years, with 16 cases reported in 2001, 10 in 2002, and only 3 cases in 2003. A total of 15 cases of meningitis were reported. Six cases of pneumonia with bacteremia and 4 cases of epiglottitis were reported. Two Hib-related deaths occurred. Twenty of these children were unvaccinated or incompletely vaccinated, and 11 were younger than 6 months. Eight of the 9 children who had completed the vaccination series were immunocompromised or had other predisposing conditions. The report noted that the number of cases in older children was unchanged from previous years and that protection did not decline with age.

In England and Wales, the Hib vaccine was introduced in 1992, and the number of invasive Hib cases in children and adults dramatically decreased. Some felt that this was because of herd immunity due to interruption of transmission from immunized children to those who were unvaccinated. However, from 1998, the number of Hib cases was noted to be rising, and, in 2002, 134 cases occurred in children aged 4 years or younger. The increase in invasive Hib in England and Wales was also seen in persons aged 15 years and older and reached prevaccine levels. This was associated with reduced antibody concentration in the older age group. This reduction in herd immunity may be due to reduced transmission of Hib organisms from persons who were vaccinated to adults who were unimmunized, providing fewer opportunities for boosting of natural immunity.

In Africa and Asia, Hib vaccination coverage is still suboptimal, [15] so Hib remains an important disease pathogen. Although measures have been taken to immunize infants and children against Hib in developing countries, the progress has been relatively slow, partly because of financing for the vaccine, sustainable immunization programs, and the need for data on the burden of invasive Hib disease. In Lambok, Indonesia, from 1998-2002, high incidences of vaccine-preventable Hib meningitis and Hib pneumonia were reported in children younger than 2 years. In a district in Malawi, Africa, the incidence of H influenzae meningitis decreased from 20-40 per 100,000 to zero in 2005 after the vaccine was introduced in 2002.

However, a study of invasive disease due to H influenzae in South Africa from 2003-2009 found an increase in the incidence the disease in vaccinated children and concluded that a revision of the Hib conjugate vaccine recommendations should be considered. [16]

In many developing countries where Hib vaccine is not administered, Hib infection is a major cause of lower respiratory tract infections and is the leading cause of deaths due to bacterial pneumonia in children. [17]

A prospective multicenter (10 primary healthcare centers) study of pediatric nasopharyngeal carriers of H influenzae was conducted in the Mediterranean coastal region of Spain, and results showed that all were NTHi. Among all the isolates, 20% were resistant to ampicillin (10% of which were beta-lactamase–producing). During winter, carriage rates more than doubled. [18]

In 12 European countries from 2007-2014, NTHi infections comprised 78% of all H influenzae cases, increasing in those younger than 1 month and those older than 20 years. H influenzae serotype f cases increased in patients older than 60 years. Hib cases decreased in patients aged 1-5 months, 1-4 years, and older than 40 years, highlighting the success of Hib vaccination. [19]

In 2017, 2 cases of Hia infection were reported in Italy, and both were of the ST23 clone (previously only known to have been present outside Europe), which was concerning. [20] In the North America Arctic area, which includes Nunavik and Nunavut, Canada, and Alaska, invasive Hia isolates also belonged to the ST23 clonal complex. [21]

In Hungary, a single-center 14-year retrospective review of adults with invasive H influenzae infection showed an annual incidence of 0.1 cases per 100,000 inhabitants. NTHi strains were the most prevalent (79%), with 14% of all isolates exhibiting ampicillin resistance. [22]

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