Hib is the abbreviation for Haemophilus influenzae type b, a bacterium which is commonly found in the throats of many healthy people, which can cause serious infection especially in very young infants or in individuals with a dysfunctioning spleen, no spleen or complement deficiency. Like many other bacteria which inhabit the throat Hib is transmitted by droplet spread from one individual to another - for instance, by coughs and sneezes. Individuals can carry Hib bacteria in their nose and throat without showing any signs of disease. However, in some people, Hib causes an invasive infection where the bacteria spread in the bloodstream to distant sites in the body.
What illnesses are caused by Hib?
Meningitis is the most common form of invasive Hib disease (approximately 60% of all cases); 15% of cases present with epiglottitis (a swelling of the throat which can lead to airway obstruction); bacteraemia occurs in 10% of cases. Other forms are septic arthritis, osteomyelitis (inflammation of the bone), cellulitis (inflammation of the skin and underlying tissue), pneumonia and pericarditis (inflammation of protective membrane of the heart). Following Hib meningitis a child may be left with deafness, convulsions and intellectual impairment; UK studies show that there is permanent neurological damage in 8-11% of cases. The case fatality rate from Hib meningitis is 4-5%.
Infants aged under one year are the highest risk group for the disease. Infection is rare in children under three months of age after which incidence rises during the first year of life, peaking at 10-11 months of age then declining steadily to four years of age. After this age the infection is uncommon.
Hib infection is a serious disease which can be prevented by vaccination. In the UK vaccination against Hib infection is included in the childhood immunisation schedule as part of combined vaccines. The first dose is given to babies at 2 months old followed by two additional doses at one month intervals and a reinforcing (booster) dose is given between 12 and 13 months of age.