Basic Science/Microbiology, Case Study - Haemophilus influenzae

Question

A 19-month-old child is brought to the emergency department following a seizure. His mother says that he had a cold for 2 or 3 days with a cough, congestion, and low-grade fever, but today he became much worse. He has been fussy and inconsolable, he would not eat and he has slept most of the morning. He then had 2 grand-mal seizures. He has no history of seizures in the past. His mother reports that he has not received all of his immunizations. She is not sure which ones he has had, but he has only had 2 or 3 shots in his life. On examination, his temperature is 100.5°F (38.1°C), his pulse is 110 beats/minute, and he appears very ill. He does not respond to your voice but does withdraw his extremities from painful stimuli. He grimaces when you try to bend his neck. His skin is without rash and results on his head, eyes, ear, nose, and throat examination, along with cardiovascular, lung, and abdominal examinations, are normal. His white blood cell count is elevated, and computed tomography of his head is normal. You perform a lumbar puncture, which reveals numerous small gram-negative coccobacilli.

What component of this organism is the target of vaccine-induced immunity?

Answers to Case 11: Haemophilus influenzae

Summary: A 19-month-old boy who has not received many immunizations presents with meningitis. The lumbar puncture shows multiple gram-negative coccobacilli.

Organism most likely causing this infection: Haemophilus influenzae type B.

• Component of this organism that is the target of vaccine-induced immunity: Purified polyribitol phosphate, a component of the H. influenzae type B polysaccharide capsule.

Clinical Correlation

Haemophilus species, particularly H. parainfluenzae and H. influenzae non–type B, are normal flora in the human upper respiratory tract. However, these strains can be associated with respiratory infections such as otitis media and bronchitis. H. influenzae type B was the most common cause of pediatric meningitis (ages 2 months to 2 years of age) until the introduction of routine childhood immunization against this bacterium.

Transmission of H. influenzae occurs by close contact with respiratory tract secretions from a patient colonized or infected with the organism. Prior viral infection promotes colonization of the respiratory tract with H. influenzae. Invasive infections such as meningitis occur when the colonizing organisms invade the bloodstream and subsequently the meninges. Usually as a result of H. influenzae type B, the capsule aids in adherence of the organism and evasion of phagocytosis. Neurological sequelae can occur in up to 20% of cases of meningitis. Haemophilus influenzae type B can also be a cause of epiglottitis in young children, which can result in respiratory obstruction requiring intubation.

Haemophilus aphrophilus and H. paraphrophilus are causes of culture-negative endocarditis, thusly named because of the fastidious nature and difficulty in recovering these organisms from the blood of infected patients. H. ducreyi is a cause of an uncommon sexually transmitted infection called chancroid. Chancroid is characterized by genital skin lesions and lymphadenopathy, which can lead to abscess formation if left untreated.

Microbiology Pearls

• Haemophilus species other than H. influenzae type B are still a significant cause of systemic infections.

• The widespread use of H. influenzae vaccines in developed countries has decreased the incidence of H. influenzae meningitis.

• Haemophilus influenzae meningitis is treated with cefotaxime or ceftriaxone.

• Haemophilus species are a significant cause of otitis (middle ear infections), sinusitis, and epiglottitis in young children.

Reference

Slack  MPE. Gram-Negative Coccobacilli in Infectious Diseases. Philadelphia, PA: Mosby; 1999.

Comprehensive Questions

Question 1 of 5

11.1

A 2-year-old child has high fever, is irritable, and has a stiff neck. Gram-stain smear of spinal fluid reveals gram-negative, small pleomorphic coccobacillary organisms. Which of the following is the most appropriate procedure to follow to reach an etiologic diagnosis?

The correct answer is A. You answered A.

Explanation:

A. The organism in the above description is H. influenzae. This organism is differentiated from other related gram-negative bacilli by its requirements of a chocolate media supplemented with growth factors, such as X and V factors, and by its lack of hemolysis on blood agar.

Question 2 of 5

11.2

Haemophilus influenzae synthesizes IgA protease, which enables the bacterium to penetrate and invade the host's respiratory epithelium. This is an example of a bacterium's ability to evade which of the host's immune system responses?

The correct answer is E. You answered E.

Explanation:

E. IgA is associated with immunologic protection of the host at the epithelial boundary. An IgA protease has the ability to breakdown IgA, thereby acting as a virulence mechanism and enabling the bacterium to invade the host through an unprotected epithelial boundary. Because IgA is an antibody associated with the humoral (specific) arm of the immune system, IgA protease allows the bacterium the ability to evade the specific humoral immunity of the host.

Question 3 of 5

11.3

An 18-month-old baby girl is suspected to have H. influenzae meningitis. She has not been immunized with the HIB vaccine. A rapid latex agglutination test is performed with the spinal fluid to make a definitive diagnosis. What chemical component in the spinal fluid are we detecting with this assay?

The correct answer is E. You answered E.

Explanation:

E. The latex agglutination test involves the use of latex beads coated with specific antibody that become agglutinated in the presence of homologous bacteria or antigen. This test is used to determine the presence of the capsular polysaccharide antigen of H. influenzae in serum or spinal fluid.

Question 4 of 5

11.4

The H. influenzae vaccine contains which of the following?

The correct answer is D. You answered D.

Explanation:

D. Encapsulated H. influenzae contains capsular polysaccharides of one of 6 types (A–F). Haemophilus influenzae type B is an important human pathogen with its polyribose phosphate capsule being its major virulence factor. As a result, active immunity is built using polyribitol phosphate antigens (capsular polysaccharide) of H. influenzae.

Question 5 of 5

11.5

CSF from a spinal tap of a patient complaining of a severe headache, fever, and nuchal rigidity revealed the presence of gram-negative coccobacilli. Further testing revealed growth of the organism on growth factors X and V supplemented chocolate agar, and no hemolysis when grown on blood agar. Which of the following organisms represents the above description?

The correct answer is D. You answered D.

Explanation:

D. Haemophilus haemolyticu s and H. influenzae are the only organisms listed above that require both growth factors X and V for growth; however, they can be distinguished from each other in that H. influenzae is hemolysis negative on blood agar, whereas H. haemolyticus is hemolysis positive.