Haemophilus (or Hemophilus) bacteria are generally harmless passengers in the upper respiratory system. One strain, H. influenzae type b or Hib, is the major disease-producing species of the genus and the prime cause of meningitis in children under the age of three. Children are now being vaccinated for it because over half are are known to be healthy carriers. The original use of a Hib vaccine reduced infection in children over two years of age, but did little for those under two, who were at a greater risk. New vaccines (conjugate vaccines) came out in 1991 and are given to those as young as two months of age.
The Haemophilus bacteria are transmitted by respiratory droplets expelled into the air. Most people develop an active antibody immunity against them by the time they reach adulthood. An infection usually begins in the nose and throat, but sometimes spreads to the sinus and middle ear or develops into pneumonia. In a small percentage of children, the bacteria spreads to the meninges, causing meningitis. This “small percentage” involves an estimated 8,000 to 10,000 cases of bacterial meningitis each year, primarily in children under five. The mortality rate of of this age group is roughly 5%. A further 25-35% recover, but suffer permanent, residual damage to the central nervous system.
In addition to bacterial meningitis, H. influenzae is responsible for other diseases, including epiglottitis, sepsis, cellulitis, pneumonia, and septic arthritis. Epiglottitis causes the tissues in the trachea to swell, posing a danger of suffocation. Those at risk are ones with compromised immune systems, who have sickle cell anemia or Hodgkin’s disease, and those without a spleen. Other less serious infections include ear infections, pink eye (conjunctivitis), and nasopharyngitis.
The name Haemophilus means “blood loving” in Greek. It was given this name because the bacterium requires special growth factors found only in blood and other body fluids. For growth in artificial media, this small, Gram-negative coccobacillus requires specific blood products called X factor and NAD, a coenzyme also known as V factor. Several other species, as H. ducreyi and H. aphrophilus are virulent, but are less common causes of infection. H. ducreyi is commonly associated with patients suffering from a sexually transmitted disease called chancroid, that is similar to syphilis.