Haemophilus influenzae

Haemophilus influenzae (not to be confused with influenza virus) is a species of bacteria that can cause meningitis and other serious infections. There are many different strains of  H. influenzae , but before the invention of an effective vaccine,  Haemophilus influenza type B (known as Hib) was responsible for around 95% of the cases of invasive disease caused by  H. influenzae  (type b is the only strain against which there is a vaccine).

Prevelance
Before the invention of an effective vaccine in the 1980s, around 1 in 200 children in the US developed invasive hib disease before the age of 5 years, with an estimated 20,000 cases of H. influenzae disease each year according to the CDC, while adults and children over 5 years old rarely developed hib infections. From 2003 to 2010, there were an average of 2,562 cases of invasive H. influenzae disease in the US each year, and it is thought that most of these recent infections were caused by strains other than type b.

Symptoms and complications
Before the invention of the vaccine, meningitis accounted for least 50% of the cases of invasive hib disease, while epiglottitis accounted for 16%, pneumonia for 15%, septic arthritis for 8%, cellulitis for 6%, bloodstream infection for 2%, and bone infection for 2%.

Of those who get Hib meningitis, 15-30% suffer hearing loss or other neurological damage, and 3-6% die, even with proper antibiotic treatment.