According to the Centers for Disease Control and Prevention, before the Haemophilus influenzae type B (Hib) vaccine was first administered in 1990, this bacterium was the most common cause of bacterial meningitis in the United States for children less than five years old. Since the vaccine, bacterial meningitis due to Hib is rare, and there is also a 99 percent decrease of all diseases caused by this bacterium.
What is it?
H. influenzae type B is a gram negative rod bacterium. One method that microbiologists have to classify bacteria is the gram stain. This is a staining process where most bacteria can be seen based on their structure. H. influenzae is called gram negative because it does not retain the first stain that microbiologists use in gram staining. The word "rod" refers to its shape.
How Does it Cause Disease?
H. influenzae has a capsule that completely surrounds it. It uses this capsule as protection against your immune system. There are six types of H. influenzae: types "a" through "f." Each type is based on the response your immune system would make against the capsule. There is also a type that does not have any capsule; this kind is called "nontypeable." All H. influenzae also have an enzyme called IgA protease. IgA are antibodies in the mucous membrane of your respiratory system; they serve as protection against foreign substances such as bacteria and viruses. H. influenzae uses its IgA protease to destroy your IgA antibodies.
Meningitis
Timothy Murphy, M.D., Chief of Infectious Diseases at the State University of New York writes in "Harrison's Principles of Internal Medicine," that type B (Hib) causes the most severe diseases of all of the types of H. influenzae. And meningitis is the most serious disease that it causes. (Meningitis is the inflammation of your meninges, the membrane that covers your brain.) If you have meningitis, you may have fever and mental confusion. The mortality rate is usually about 5 percent. If you recover, you may suffer with hearing problems, paralysis and seizures.
Pneumonia
Pneumonia is an infection of the lungs. Hib can cause pneumonia in infants, adult smokers, and adults who have COPD. (COPD is a disease where your lungs are slowly destroyed by emphysema or chronic bronchitis.) If you have pneumonia, your symptoms may include sudden chills, fever, cough and chest pain.
Cellulitis
Damian Dhar, M.D., of the Atlanta Dermatology, Vein and Research Center explains in "The Merck Manual for Healthcare Professionals," that cellulitis is the inflammation of the skin and the tissues that lie just beneath it. If cellulitis is caused by Hib, then it usually affects young children. They may have cellulitis on their neck or head. Sometimes, the infected area looks bluish-red.
Epiglottitis
Epiglottitis is the inflammation of the epiglottis. Hib can cause epiglottitis in children who are between 2 to 7 years old. If untreated, it can be life-threatening because the swollen epiglottis can interfere with the child's ability to breathe. Thus, in trying to breathe, a child will usually lean forward, with his chin "sticking out." He may also have a high fever that started suddenly, drool and have a difficult time eating.
References
- Centers for Disease Control and Prevention: Chapter 2 - Haemophilus influenzae Type b Invasive Disease
- "Harrison's Principles of Internal Medicine"; Anthony Fauci, M.D., Dennis Kasper, M.D., Dan Longo, M.D. et al.; 2008
- The Merck Manual: Cellulitis
