Haemophilus influenzae type b (Hib)
Symptoms and Causative Agent
Haemophilus Influenzae type b, commonly known as Hib, is a bacterium that can cause severe infections, particularly in young children. Despite its name, it is unrelated to the influenza virus: Hib was found in a group of patients during an influenza outbreak in 1892, before scientists discovered that the flu was caused by a virus. Hib was thus proposed as the cause of influenza. Its now-confusing name was kept in spite of its initial, though incorrect, association with the flu.
Hib bacteria can cause many types of invasive disease, including meningitis, pneumonia, cellulitis (skin infection), septic arthritis (joint infection) and epiglottitis (infection of the epiglottis, causing obstruction or closing of the windpipe). Thus, although it’s sometimes said that the Haemophilus influenzae type b vaccine is given to “protect against Hib,” this phrasing is not technically correct. The vaccine protects against the diseases caused by Hib, which are numerous and can be severe. Collectively, these Hib-caused infections are referred to generally as “Hib disease.”
Before the Hib vaccine was introduced, meningitis—infection of the membranes that cover the brain—was the most common Hib-induced invasive disease. Symptoms include fever, stiff neck, and impaired mental status. Meningitis results in permanent hearing impairment or other neurological conditions in 15-30% of patients who survive it.
Haemophilus influenzae type b bacteria can’t survive on surfaces or in the environment. The bacterium’s only known reservoir is humans, who may carry it without becoming ill.
It is thought to be spread through the air by respiratory droplets from sick individuals. Fortunately, its ability to spread is considered limited in most cases, although close contact with an infected patient can lead to outbreaks.
Treatment and Care
Antibiotics may be used to treat Hib infections, but the bacteria have developed resistance to some antibiotics. Hospitalization is often required.
Because the spectrum of Hib disease ranges from meningitis to pneumonia, the types of complications vary depending on the type of Hib infection. Many of these are forms of neurologic damage, including blindness, deafness, and mental retardation.
As with the complications associated with various forms of Hib disease, the risk of death from the different types varies. For Hib meningitis (the most common form of invasive Hib disease), the case fatality rate is 2-5%.
Before Hib vaccination, about 20,000 children younger than five developed severe Hib disease in the United States each year, and about 1,000 died. By 2006, the number of reported Hib cases was down to only 29 for the year. Now, while the majority of fatalities from Hib disease are reported in developing countries where the Hib vaccine is not widely used, fatalities still occur in developed nations when vaccination rates drop. Seven cases of invasive Hib disease were reported in Pennsylvania during a six-month period starting in October 2008. Only one of the children had received a Hib vaccination (and had received only one of the recommended doses). Three of the children died.
Available Vaccines and Vaccination Campaigns
The first vaccine to protect against Hib diseases was introduced in the United States in 1985; an improved vaccine was licensed two years later. Several preparations of Hib vaccine are now available, both as single vaccinations for Hib and in combined shots (Hepatitis B and Hib vaccines, for example, are available in a combined shot). All of the vaccines against Hib disease are inactivated vaccines and contain only a part of the Hib bacterium.
U.S. Vaccination Recommendations
Vaccination against Hib disease is included on the U.S. childhood immunization schedule. Either three or four doses are recommended depending on which Hib vaccine is being used. For all Hib vaccines, however, the first dose is recommended at two months of age, and is not generally recommended beyond five years of age.
Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Haemophilus Influenzae type b. Atkinson W, Wolfe S, Hamborsky J, McIntyre L, eds. 11th ed. Washington DC: Public Health Foundation, 2009. http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/hib.pdf. (524 KB). Accessed 7/31/2014.
Centers for Disease Control and Prevention. Hib Vaccination. http://www.cdc.gov/vaccines/vpd-vac/hib/default.htm Accessed 7/31/2014.
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Last update 31 July 2014