Bacterial Meningitis: Definition

00:01 We turn now in our discussion of central nervous system infections to bacterial meningitis, a very serious infection indeed.

00:13 So, we would define bacterial meningitis as an infection of the meninges, of the coverings of the brain, specifically the subarachnoid space and brain as well.

00:27 It's really a meningoencephalitis, usually due to any of a variety of blood-borne microorganisms.

00:41 Now, among the causes of acute meningitis, actually viruses probably account for most cases of acute infection of the meninges, but viral meningitis is generally a benign disease.

00:57 It’s not terribly serious.

00:59 It’s troubling for the patient, but they get over this kind of an infection.

01:04 But blood-borne bacteria can cause a life-threatening problem.

01:10 Now, when a physician can't tell which it is, is it viral or is it bacterial, then that physician would be prudent to start antibiotics just in case it is bacterial.

01:26 Now, among the bacteria that cause meningitis – and there are many – these are the top five.

01:34 Streptococcus pneumoniae, Neisseria meningitidis, Streptococcus agalactiae also known as group B Strep, Listeria monocytogenes, and Haemophilus influenzae.

01:50 Haemophilus influenzae was the most common cause of meningitis in the past, but because we now have a vaccine against that particular organism, Haemophilus influenzae type B, it is no longer the most common cause of meningitis.

02:14 Now, turning to the epidemiology, we need to look at the causes of meningitis first among newborns.

02:23 And here, group B Strep, Strep agalactiae accounts for about 70% of the infections of the meninges, followed by Listeria and by the pneumococcus.

02:37 From one month to two years of age, look what is now top cause.

02:43 Streptococcus pneumoniae.

02:44 As I mentioned, in the past, it was Haemophilus influenzae, but that has essentially vanished in developed countries.

02:53 Neisseria meningitidis and Strep agalactiae follow behind.

02:59 From the age of two to the age of young adults, Neisseria meningitidis causes about 60% of the cases of meningitis, followed by the pneumococcus and Haemophilus influenzae.

03:16 In adults, the pneumococcus tops the list, causing 60%, with Neisseria meningitidis causing 20% and the others are relatively rare causes.

03:30 But by the age of 60 years plus, the pneumococcus accounts for most cases of bacterial meningitis and Listeria moves up the list, accounting for about 20%.