Prior to the introduction of a vaccine, what was the leading cause of bacterial meningitis in children under 5 years of age?

The leading cause of bacterial meningitis in children under 5 years of age, prior to the widespread introduction of the Haemophilus influenzae type b (Hib) vaccine, was indeed Haemophilus influenzae type b. This organism is a type of bacteria that can cause severe infections, particularly in young children and infants.

Before the vaccine became available, Hib was responsible for a significant number of cases of bacterial meningitis, as well as other serious infections such as pneumonia and epiglottitis. The vaccine has been instrumental in dramatically reducing the incidence of invasive Hib disease among children, showcasing the importance and effectiveness of vaccination programs in preventing deadly infections.

Other options such as Streptococcus pneumoniae and Neisseria meningitidis do cause bacterial meningitis, but they contributed less to the overall incidence of meningitis in young children compared to Hib before the vaccine existed. Escherichia coli is more commonly associated with neonatal infections rather than bacterial meningitis in children under 5 years of age, making Hib the correct association for this question.