00:01
In this lecture,
we're going to discuss the febrile baby.
00:05
If you've done a
pediatric rotation
and have spent some time
in the inpatient setting,
you've probably encountered
a baby who was febrile
who was admitted for what
we call a rule out sepsis
making sure that there's not a
more significant cause of illness.
00:20
I'm going to try and break that
down for you here and make it clear
so we can understand how and why we
manage the babies that way we do.
00:28
A febrile infant is defined as any infant
with a fever over 38 °C or 100.4 °F.
00:36
We use to define serious
bacterial infection
a little bit differently
than we do now.
00:41
And that's because we've discovered
that urinary tract infections
really aren't as bad as
we thought they were.
00:46
So, serious bacterial
infection is typically defined
as meningitis or bacteremia.
00:52
But urinary tract infection
is no longer considered an SBI
because the outcome of these
infants is actually fairly mild.
01:01
The AAP febrile infant guideline breaks
down infants into three distinct groups.
01:06
The first group is 8 to 21 days.
01:09
Notice we're skipping 0 to 7,
realistically those infants just
go home from the newborn nursery
or they may come back
to the newborn nursery
if they're febrile that
quickly after birth.
01:19
Then there's the
22 to 28 day group.
01:22
And then there's the
29 to 60 day group.
01:24
And these are treated a
little bit differently.
01:27
Let me go through
them one at a time.
01:29
For infants in the first three
weeks of life from 8 to 21 days,
all these infants should get a
urinalysis, a urine culture.
01:37
Keep in mind that 10% of infants in this
group will have a urinary tract infection.
01:43
We will obtain that by catheter or
suprapubic tap rather than the clean catch.
01:47
And we'll use a very
strict cut off 10,000 CFU
as defined as a urinary
tract infection.
01:55
Note that's a little bit different
than two months to two years of age
where we typically use
50,000 CFU as a cutoff.
02:04
We should get a blood culture.
02:06
Keep in mind that between about 4 and 5%
of infants in this group have bacteremia.
02:11
Now 20% of the infants
with UTI have bacteremia.
02:14
So a bunch of them are from UTI.
02:18
But also keep in mind that
between 60 and 90% of these kids
have fake positive cultures.
02:25
These are contaminants.
02:26
So, when you get a blood culture,
chances are it's a contaminant.
02:31
If it's not a contaminant,
it's probably from a UTI.
02:34
But a reasonable
percentage around 1 or 2%,
it will be true bacteremia absent
of UTI so we have to look for this.
02:42
Also in the first three weeks of life,
we really should get a spinal tap.
02:45
And when we send the spinal
tap fluid for testing,
we're going to get a white
count, a protein,
a glucose,
a gram stain and a culture.
02:54
We're also going to
do an enterovirus PCR.
02:57
Because during
enterovirus season,
if that's positive,
it can really simplify care.
03:02
If there's a pleocytosis or if this
infant is at high risk for HSV,
which we will talk about
in another lecture.
03:08
We will also send the HSV PCR.
03:11
Some centres are sending these children's
CSF for something called a multiplex PCR.
03:16
This is a panel that
looks for lots of bacteria
that might be in the
child's spinal fluid.
03:22
The problem is, we are really instructed
by the AAP, we should not use this test.
03:27
And the reason is, is because there are
false negatives and false positives.
03:31
And also listeria isn't
often on the panel
and listeria can cause
meningitis in infants.
03:37
Additionally,
one thing that some people are taught
is that, hey,
if you get a bloody tap,
you can correct for
the amount of blood
to estimate the
number of white cells.
03:45
And there's various formulas 400 to
1, you do the math.
03:49
In fact,
we should not correct for blood.
03:51
And the reason is, is because if you do
that you will actually miss some infants
with pleocytosis and
bacterial meningitis.
03:59
So for these kids,
up to the first three weeks of life,
we're going to admit
them to the hospital.
04:04
We're going to start
ampicillin gentamicin.
04:07
Unless the CSF is consistent
with bacterial infection,
then we would start
Ceftazidime and Gentamicin.
04:12
We do not need to be doing antibiotics
if the enterovirus PCR is positive.
04:17
Enterovirus PCR is
really interesting test
and it's really beyond the scope
of this lecture to get why.
04:22
But the false positive rate of
this test is essentially zero.
04:26
So if you see enterovirus, that's what
it is, you can stop the antibiotics.
04:30
You might not discharge the
kid if they're very sick,
but you can certainly
stop the antibiotics.
04:35
Then you will discharge
the patient home
after the cultures are negative for 24 to
36 hours and the baby's looking better.
04:43
Now, it's a little bit different
for this fourth week of life
and I want to sort of get into why
because I think it's pretty interesting.
04:50
So you will still get a
urinalysis, urine culture
both again by catheter
or suprapubic tap
And if you want,
you can get a bag urine
and if that's negative,
skip the cap or the suprapubic tap.
05:04
However, it's positive,
then you do have to repeat the culture.
05:07
And the reason is,
is that bag urines have a very
high false positive rate
for bacterial culture.
05:13
Then you'll get a blood culture.
05:14
Keeping in mind that
still a fairly substantial
number of these infants
have bacteremia.
05:19
And also remember that the
huge number who have UTI,
about 7.5 to 10% of
them have bacteremia.
05:26
So that's fairly common.
05:28
Here's the kicker.
05:30
You also should assess an
inflammatory marker in this child.
05:33
And what many have been
taught is that the white count
is an accurate
inflammatory marker.
05:39
And that is in fact, untrue.
05:42
The WBC count for
infants does not reflect
whether they're likely to have
bacterial versus viral infection.
05:49
The abnormal inflammatory markers
you can include are the ANC,
which if it's over
4000 is abnormal.
05:57
Keep in mind, that's the white count
times the percentage of bands plus segs.
06:01
So if you have 50% segs and a
white count of 10, that's 5000.
06:06
And that would be abnormal.
06:08
That's not as good as a marker
as the CRP or the procalcitonin.
06:13
For CRP, we'll use an abnormal
number of greater than 20.
06:17
And for procalcitonin,
we'll use an abnormal number of 0.5 ng/mL.
06:23
So let me explain why white
count is not accurate.
06:26
Because there's a lot
of students out there
who are still being told
white count is the way to go.
06:30
And it really isn't.
06:32
And to get it that you have to
use something called an ROC curve.
06:35
This is a little bit off topic.
06:36
But I think, it's incredibly important
for us to understand what an ROC curve is.
06:40
We use an ROC curve to figure
out what that number should be.
06:44
If you recall, we said what the CRP
should be more than 20 to be abnormal.
06:50
Well,
where do we get that number 20?
Well, what we do is we look
at the test and we say,
what is the true positive rate and
what is the false positive rate?
Remember, true positive rate is the
number of positive tests in sick people.
07:02
And the false positive rate is number
of positive tests in the healthy people.
07:06
It makes sense.
07:07
And we're just going
to graph it here.
07:09
So let's say these are a bunch of
children who are getting a white count,
and the blue ones do not have
disease and the red ones are sick.
07:17
And these are what
their white counts are.
07:19
Well, what should
we use as a cut off?
Let's pretend I said,
any white count over one is abnormal.
07:27
Well, every single patient
has an abnormal white count.
07:29
So the true positive
rate is 100%.
07:33
But also the false
positive rate is 100%.
07:36
So we'll plot that point right
there in the top right corner.
07:39
What if I said 20 was abnormal,
then nobody on this panel
of patients has an abnormal
and therefore the true
positive rate is zero
and the false positive rate is zero
plotted right where that 20 is.
07:52
But what if I used
a cut off of 10?
What you can see is that
about 3 out of 7 of the babies
would be abnormal,
who are healthy.
08:02
And unfortunately,
about 4 of the 7 babies
who have the disease
would be abnormal.
08:10
And so this is not a
particularly accurate test.
08:14
And you see sort of like a
straight line on that graph.
08:18
But let's look see what
a good test look like,
let's pretend we're
looking at procalcitonin.
08:24
And we say, okay, well,
of our healthy babies,
these were the numbers they had
ranging from between 0.2 and 0.6.
08:31
And of our sick babies, it's between
somewhere between 0.4 and 1.2.
08:35
Well, if we set an abnormal test was
0.1, everyone would be positive.
08:41
if we set an abnormal test was
2, everyone would be negative.
08:45
But what if we used an
abnormal cutoff of 0.5?
Well, that's kind of cool.
08:51
You could see that only 1 child of
the 7 would have a false positive,
and only 1 child in the sick
group would have a false negative.
09:02
So we plot that you
can see that 0.5 number
is a little bit closer the
top left corner of the graph.
09:09
So what you want
to see in a test
is a curve where it
bends up the top left,
and then we look at the
area under the curve.
09:16
And remember,
the white count was a straight line.
09:18
So that was half of the
graph and half is useless.
09:22
One would be a perfect test.
09:24
So the closer the area under the curve
is to one, the better the test is.
09:28
Well,
here's the data for children.
09:30
And what you can see is the
procalcitonin gets very close to one,
the CRP and the ANC
are a little bit less,
and then the white count
is absolutely useless.
09:40
So this is why we do not recommend
a white count in children
who have fever who are infants when
we're testing them for bacterial disease.
09:48
Let's get back to the guideline.
09:50
In the fourth week of life,
the CSF may be obtained
if the inflammatory
markers are negative.
09:56
You've got the
urine in the blood.
09:58
The child is hospitalized and the UA
result doesn't affect this recommendation.
10:02
In other words,
they have a UTI or they don't,
kids in the hospital
inflammatory markers are normal,
and you don't have to get an LP.
10:11
You should get an LP however, if
there's an elevated inflammatory marker,
so that's why we're
getting that marker.
10:17
And specifically,
the white count isn't one of them,
you really should go a CRP or procalcitonin
if you can get it at your institution.
10:25
Let's go through some examples.
10:26
So if we had a 26-day
old well appearing infant
in the ER with fever and upper respiratory
infection, not really bronchiolitis.
10:34
His temp is 100.7.
His CRP is 2 mg/L.
10:37
That's really low.
Remember, 20 is our cutoff.
10:40
You have a urine and a blood culture
pending, therefore, you can skip the LP,
but you should do it if the parent
or you are still otherwise concerned.
10:48
You were like, "Maybe that was
a seizure when he was shaking,
I should just double check.
I think I'll do the LP."
That's fine.
10:55
But example B is a 27-day
old well appearing infant
in the ER with fever
and nonbloody diarrhea.
11:01
His temp is 100.6.
But as CRP is high at 24 mg/L,
you should do the LP.
11:06
So I hope you get the difference between
how we think about those two circumstances.
11:11
So in that four with
fourth week of life,
we are going to hospitalize them
if the CSS CSF testing is abnormal,
and then we're going to treat
either with ceftriaxone,
not ceftazidime, which is what
we're using at the little infants
because that is subtraction is
contraindicated in jaundice babies,
or you can do ceftazidime and vancomycin
to cover resistant strep pneumo.
11:34
You're also going to hospitalized
that the CSF is normal,
the UA is normal, but the CRP is
abnormal, and you put them on ceftriaxone.
11:41
If all the labs are normal, and somebody is
worried parent, doctor or nurse, whoever,
then sure,
go ahead and observe them.
11:48
You can either observe
them on or off ceftriaxone.
11:51
And if all labs are normal,
and the parents want to go home,
you can send them home.
11:56
So this is an interesting
guideline because it's allowing
parents to help make a
decision which I kind of like.
12:01
Now what about 4 to 8 weeks,
this is a little bit simpler.
12:04
You're gonna get a UA
and a urine culture.
12:06
You're going to send
a blood culture.
12:08
You're going to check
inflammatory markers.
12:10
If it's high, consider an LP
but you don't have to do it.
12:13
If it's normal, consider discharging
home but you don't have to do it.
12:17
And you may treat a well appearing
infant with a Urinary Tract Infection
with oral antibiotics
and send them home.
12:23
You do not have to
hospitalized an infant
with a urinary tract
infection at this age.