Haemophilus influenzae type b (Hib)

Haemophilus influenzae type b (Hib) is a bacterium that often causes severe infections, especially in children under the age of 5.

Haemophilus influenzae type b (Hib) is a bacterium that often causes severe infections, especially among children under the age of 5. Hib usually causes a flu-like illness, which resolves within a few days. However, in some cases, the infection can evolve into severe forms called invasive forms.

In Haemophilus influenzae bacteria, a capsule is present. Six different types of haemophilus are described based on the composition of this capsule, named from A to F. Hib is responsible for 95% of all invasive haemophilus cases in susceptible people and is a major cause of infections that are especially fatal in infants.

Transmission routes

Transmission occurs through direct contact, with inhalation of droplets emitted in the nasopharyngeal secretions of patients and/or carriers; since the introduction of the vaccine, carrier status has become rare. The two seasons in which Hib spreads most from one subject to another are autumn and spring. The infectiousness of Hib is limited, although, in the case of communities such as nurseries and schools, small outbreaks can occur.

Symptoms and complications

The invasive diseases caused by Hib can affect several organs. The most common types of invasive disease are meningitis, epiglottitis, pneumonia, arthritis, and cellulitis.

  • Meningitis is an infection of the membranes that cover the brain and is the most common of the invasive Hib diseases, accounting for 50 - 65% of cases in the pre-vaccination era. The typical symptoms of meningitis are fever, altered mental status and stiffness in the neck. The mortality of Hib meningitis is 2-5% even with appropriate antibiotic therapy. However, those who recover from meningitis can have neurological consequences, which occur in 15 -30% of patients.
  • Epiglottitis is an infection of the epiglottis, the structure in the throat that covers and protects the larynx during swallowing. Epiglottitis is dangerous because it can cause airway obstruction with the risk of death from suffocation.
  • Other common manifestations of invasive disease are septic arthritis (joint infection), cellulitis (a rapidly progressing skin infection that usually affects the face, head, or neck), and pneumonia.
  • Osteomyelitis (bone infection) and pericarditis (infection of the sac that covers the heart) are less common forms of invasive disease.

Impact on the population

The World Health Organisation has estimated that in 2000, haemophilus influenzae caused globally 2-3 million cases of invasive disease - mainly pneumonia and meningitis - and 386,000 childhood deaths. Hib disease is observed worldwide but it is difficult to accurately estimate its extent as confirmation of the disease requires the timely execution of laboratory tests. In general, however, different manifestations of the haemophilus B disease is observed between developing countries and industrialised countries. In the former, the main manifestations of Hib disease are infections of the upper airways and pneumonia. In industrialised countries, on the other hand, Hib disease occurrs primarily as meningitis or as sepsis.

In the United States, in the pre-vaccination era, about 20,000-25,000 cases of Hib meningitis were reported each year. Anti-Hib vaccination, introduced in the USA in 1987, has led to a drastic reduction in cases of illness; only two years after its introduction, the disease had almost disappeared.

In Europe, according to ECDC (European Centre for Disease prevention and Control) data, in 2010 2,044 cases of invasive Haemophilus influenzae disease were reported. In Italy, given the seriousness of these diseases, a national meningitis surveillance system has been active since 1994; this was set up by the Italian Ministry of Health and coordinated by the National Health Institute (ISS) with the participation of all the Regions. In this country, since the introduction of the anti-Hib vaccine in 1995, there has been a progressive decrease in cases of the disease, dropping from 63 cases reported in 1998 to 5 cases in 2003. The incidence has fallen from 5, 5/100,000 cases per year to 0.6/100,000 cases.

These significant results can be attributed to the high vaccination coverage in the country. In Italy, only one case of invasive disease resulting in death was reported in 2012.

Incidence of invasive Hib diseases in children under the age of 5 in Italy

Clinical case

Meningitis, death of a child on holiday

Ancona, 25 July 2012 - Il resto del Carlino

The tragedy: the prior disease was fatal, death on Tuesday. – HE DID NOT MAKE IT: the 5-year-old boy who had been admitted to the Salesi hospital on Friday night for a serious form of bacterial meningitis died yesterday afternoon. In the end, the inflammation gained the upper hand and death occurred due to a previous illness which the child suffered before admission and which compromised his immune system. The child had arrived at the Ancona Maternal and Children’s hospital in a serious condition, after being struck by haemophilic meningitis (Haemophilus influenzae type b), a bacterial form that is more frequent in children under 5 and which is difficult to cure. Despite this, the doctors maintained hope of saving the boy, whose condition had stabilised. Yesterday, however, the tragic epilogue. The child was taken in the late afternoon of Friday to Salesi and admitted to an isolation room in the Intensive Care Unit of the Maternal and Children’s hospital of Ancona...

Alessandra Pascucci (Il Resto del Carlino)

Photo 1: Infectious cellulitis from Haemophilus influenzae type b

Sources / Bibliography
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