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Germs that infect humans

Haemophilus influenzae

Haemophilus influenzae

© Dennis Kunkel Microscopy, Inc.

Microorganism: the bacterium Haemophilus influenzae type b.

Disease: bacterial meningitis

Occurrence of the disease

History: prior to the introduction of a vaccine against Haemophilus influenzae, this microorganism was the greatest cause of bacterial meningitis in children younger than six years old. In 1998, eighteen cases of Haemophilus influenzae type b infection were reported in Quebec.

Mechanism of action of the microorganism: the bacteria multiply in the nasal passages before spreading to the blood and to the liquid surrounding the brain. Once they reach the liquid surrounding the brain, they produce inflammation of the meninges (the membranes surrounding the brain).

Symptoms of the disease: the initial symptoms of meningitis are sore throat, vomiting, headache, confusion, and stiffness in the neck and back. Eventually, meningitis (inflammation of the membrane surrounding the brain) occurs. The mortality rate is five per cent, and 20-45% of survivors suffer serious long-term effects such as mental retardation and deafness.

Incubation period: unknown, but probably two to four days.

Contagious period: as long as the microorganism is present. When adequate therapy is applied, however, this is reduced to 24-48 hours.

Hosts: humans.

Transmission: contact with nasal secretions from an infected individual.

Discoverer of the microorganism: Weichselbaum in 1887.

Treatment of the disease: antibiotics such as penicillin; 30% of Haemophilus influenzae type b strains are ampicillin-resistant.

Geographical distribution of the microorganism: worldwide.

Prevention: vaccination. Non-vaccinated individuals coming into contact with infected individuals may take Rifampin.

Vaccine: the vaccine currently used against bacterial meningitis is known as the DTP-Polio-Hib vaccine, and is in fact a combination of several vaccines that provides protection against diphtheria, whooping cough, tetanus, polio, and Haemophilus influenzae type b infections. The specific Haemophilus influenzae vaccine (Hib) is produced from bacterial cell walls. The vaccine is more than 90% effective against Haemophilus influenzae infection when administered to children two to five months old. Booster injections of the vaccine must be administered two, four, six, and 18 months after the initial vaccination.

Meningitis may also be caused by other microorganisms, such as the viruses responsible for measles, chickenpox and herpes, and the bacteria Neisseria meningitidis. A vaccination program against Neisseria meningitidis, which causes type c meningitis, was conducted in Quebec in 2001, and resulted in a reduction of the incidence of infection from 1.3/100,000 to 0.3/100,000.