Bacterial Meningitis

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Bacterial Meningitis : Dr. Charles Prober discusses prudent prescribing of antibiotics in the context of bacterial meningitis with 4th year medical student Morgan Theis

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We're here at Stanford Medical School with 4th-year medical student Morgan Keyes and Dr. Charles Prober.
MK: Okay, Dr. Prober, what are we going to talk about today?
Dr: So Morgan, I thought we'd talk about Bacterial Meningitis in children.
MK: Okay.
Dr: And what I'd look to do in reflecting on bacterial meningitis (BC) is...
...go back to the lessons we learned in the prudent prescribing of antibiotics.
Dr: a former video, a prior video.
Dr: One of the things that was mentioned as a general principle in that particular video
was trying to understand where the site of infection is in a child,
in order to pick the right antibiotic and the right management.
Dr: So in this case, since I'm referring to BC, the question might be:
What would make you think that a child has BC?
That is, what are the signs and symptoms of BC?
Student: So this is thinking about the site, knowing that there is an infection in the
cerebrospinal fluid (CBF), or fluid around the brain and spinal cord, you have to look at that
in a variety of ways as a doctor?
Dr: Exactly. One of the things that will make a physician suspicious that there might be
an infection in the CBF or in the central nervous system (CNS),
is that a child might not be behaving normally,
that is, they might have an altered state of consciousness.
E.g., they might be very, very sleepy; or, they might be very irritable
Student: So the signs are irritability and/or sleepiness (lethargic),
maybe even in a coma, which would be more advanced in the infection.
Dr: And then the child would almost invariably have that fever associated with this illness.
And, on the examination, when the physician examines the child,
they might detect what are called "meningeal signs".
And those meningeal signs include a stiff neck, especially if the child is over 1 or 2 years of age,
Student: And how can you tell if someone has a stiff neck?
Dr: What a physician will often due is hold the child behind the head and try
try to flex the head on the neck, and stiff would be literally that:
the child's neck would not bend when the head is elevated from the bed.
Student: Wow, so it's literally where it stays linear, you can't curve it well.
Dr; Exactly. The other meningeal signs that may be present in addition to the stiff neck are
the child may have some seizures, abnormal movements.
The child might also assume an abnormal posture, a stiffening of the body.
So, not just the neck being stiff, but the rest of the body being stiff as well.
And on examination of the neurologic system, the nervous system,
the child might have "focal signs," that is, asymmetry between the two sides of the body.
Student: Oh, and what kinds of things would you see that are assymetrical?
Dr: It could be that one side of the body is weaker than the other,
It could be that one of the body has different reflexes than the other side.
These are all signs and symptoms which may be associated with BM,
which would make the physician suspicious of the diagnosis of meningitis.
Student: Okay, so we talked about some of the things you look for as a doctor. Now,
going back a minute, you said something about BM, does that assume that there
are other types of meningitis that we are not addressing in this lecture?
Dr: That is a very important point. So, I am focusing on BM,
there are other types of organisms, non-bacteria, that can cause meningitis,
and the most prominent of those other organisms are viruses.
So you can have a viral meningitis, sometimes referred to as aseptic meningitis.
And that in fact is more common that bacterial meningitis, so it is very important to consider.
There are also some parasites that can cause meningitis, and some fungi.
The fungi and parasites are uncommon, but they may occur in abnormal immune systems
Viral meningitis on the other hand is quite common.
But for today I am focusing on bacterial meningitis.
So you suspect the infection may be present based on those signs and symptoms.
To prove, to determine whether meningitis is present,
a cerebrospinal fluid (CSF) examination [must take place],
and CSF is acquired by doing a lumbar puncture,
putting a needle in the back to obtain fluid.
Student: Is that also what a spinal tap is?
Dr: That is also called a spinal tap
When that is obtained, using a needle into the lumbar area,
a fluid is then sent to the lab, where the fluid will be examined in different ways
One is to look under the microscope and determine if there is an abnormal number
of white blood cells present.
Student: So abnormal meaning high or low?
Dr: Meaning just high, actually.
The normal number of white blood cells in the CSF is 0.
So, high is something greater than 0. And with BM, it tends to be quite high.
generally 1,000-2,000/mL.
Glucose is also measured, and with BM the glucose tends to be low
less than 40.
Student: Why would it be low?
Dr: It's low because with meningitis you have an abnormal penetrability,
or lack of penetrability of the meninges, which are the covers of the brain,
reducing the amount of glucose that is transported into the spinal fluid.
Dr: And then most importantly, the fluid is examined with something called the Gram stain,
a special kind of stain. A Gram stain can determine if bacteria are present.
Student: So you're actually staining the bacteria.
Dr: Exactly. And if sufficient bacteria are present the Gram stain will reveal those.
And so, with BM, the 2nd prudent principle is to know the pathogen.
So, if a spinal fluid is obtained, there is lots of white cells, your glucose is low,
even with a negative Gram stain, one can guess the usual pathogens,
because the list is short in normal children.
And those bacteria, the short list, includes "Haemophilus influenzae" tybe B,
2nd, the Pneumococcus.
Student: That's funny, it sounds like it causes pneumonia.
Dr: It does cause pneumonia, indeed.
3rd: Meningicoccus.
Dr: Those are the prominent bacteria in normal children with BM.
The reason we're not seeing as much BM in 2011 as we were seeing 10 or 20 years ago,
is we now have vaccination against each of those three pathogens.
Student: We do?
Dr: We do. We vaccinate against "H. Influ. B" starting at two months of age
and by the time the child is about 1.5yrs, they're completely protected against that bacteria
The Pneumo we also vaccinate against and it's very successful at reducing
the frequency of pneumococcal meningitis--also given at 2 months of age.
And Meningicoccus, the vaccination is relatively new and used in children who are older
They're now 2yrs of age.
So, we still can and do see cases of meningicoccal meningitis as it occurs
in children under the age of 2.
Those are the usual pathogens. In other parts of the world that don't use vaccines,
those are the pathogens that will be prominent in causing BM.
And knowing those pathogens, we go to the 3rd Principle of antibiotic prescribing,
which is knowing antibiotic would potentially kill those bacteria.
Student: Okay, so what should I call that category?
Dr: Pathogen sensitivity, knowing which antibody would work against the likely bug.
Student: That, you were mentioning in your last lecture,
that varies by the location in the body, and the location in the world, where you're using it.
Dr: It varies by the location of the world, but not by part of the body.
And, fortunately, for the treatment of BM, to cover all three of the bacteria,
two antibiotics cover all three of them, and I'll just mention the names as I end this.
One antibiotic is Cefotaxin, and a reasonable facsimile is Ceftriaxone.
And because some of the Pneumo are resistant to Beta-lactam drugs,
Vancomycin is also used for suspected BM.
Student: Okay, so we use Vancomycin if we think you have a bug that is resistant to other drugs?
Dr: Exactly.
Student: And there is a type of lab test you could do to find that out?
Dr: Exactly. So those are the Principles of antibiotic prescribing, in terms of
diagnosis of BM. 1) Knowing site of infection
2) What the pathogens are, and 3) knowing what antibiotic would work.
Student: My last question, just because we learned about a tight barrier between
the blood and the CSF, are these antibiotics listed here able to cross the barrier?
Dr: An extraordinarily important question, which is another principle:
You have to make sure that they can be delivered to the suspected site of infection.
For those antibiotics, the answer is, "Yes."