The Febrile Baby: Urinary tract infection (UTI), Bacteremia & Meningitis

by Brian Alverson, MD

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    00:00 Okay, let's get away from HSV because I really want to focus on bacterial causes of children being sick in the hospital with a fever. The most common by far risk is urinary tract infection and this typically happens between 5 and 10% of the time, perhaps 10% in the first month and 5% after that. Bacteremia is relatively rare, about only 1% of the time, and meningitis is even rarer than that. So, the bacteria that cause these illnesses are very much the same, they're bacteria that the child is exposed to during the delivery process. Delivery is not a sterile phenomenon as you probably seen if you've been at one. So there are risks for mostly fecal organism such as <i>E. coli</i> or vaginal organisms such as group B strep especially in GBS positive mothers who are undertreated or untreated. <i>Strep pneumoniae</i> is not a typical bacteria that kids are _____ at the time of birth but it absolutely can cause sepsis in these children, although it's much less likely than in an older child. Likewise, <i>Neisseria meningitidis</i> is incredibly rare to get as a result of the birthing process but can rarely happen. <i>Enterococcus</i> is more of a fecal as is <i>Klebsiella</i> and we're seeing more and more <i>Staph aureus</i> in these newborns as we're seeing more aggressive <i>Staph aureus</i> types like MRSA or resistant <i>Staph aureus</i>, we are seeing it now and then and there can sometimes be outbreaks in newborn nurseries. Okay, I'm worried about urinary tract infection because that's the most common cause of bacterial illness in these children. What do I do? Whenever we get a test, we want to ask "Is it sensitive or specific?" In the case of this, we have 2 ways we can check labs in these kids. We can get a bag or we can get a urine. If a child has a urinary tract infection, the bag is more sensitive. It's more likely to be positive.

    02:07 If a child does not have a urinary tract infection, the cath is more likely to be negative.

    02:13 It's more specific. In general, in the United States, we've decided that the cath specimen is superior. Now there are some ways you can work around this. If you have time you might bag the child and if the bag is negative then you're done and then proceed the catheterization if it's positive but most centers just go straight to catheterization or alternatively if you're incapable of getting urine any other way, you might do a suprapubic tap. That's where we insert a needle directly into the bladder through the abdominal wall to get the urine. It's actually a fairly safe procedure, although how successful it is depends on the experience of the practitioner but in general in the United States we prefer to go to cath or suprapubic tap as opposed to what they recommend in England. The reason we went that way is because there is more and more a feeling that these urinary tract infections are not as serious as we've previously suspected.

    03:12 Kids tend to get better and many times it's not truly a UTI but it's bacteriuria, a benign shedding of bacteria in the urine. Okay, if we get that urine we're going to send it for a urinalysis and the urinalysis has several aspects on it that tell us whether the child is likely to have the disease. Remember, the more tests you get you improve your sensitivity and you lose your specificity. So if we look at the individual elements you can see that these all have different amounts of sensitivity and specificity. The one I would call your attention to is nitrites. It's 98% specific. That means if you have a positive nitrite on your urine dip, it's very likely that child has a UTI. Overall, the UA is a very sensitive test. It's 97% sensitive and has a high false positive rate, 30% false positive rate. So if a patient has UTI, it's almost always positive but it can be positive in normal individuals. Remember those 3 numbers. How do we approach bacteremia? Very ill children may have overwhelming bacteremia or bacterial sepsis and this is more common in infants than it is in older children. Untreated sepsis can lead to shock and death. So we do worry about bacteremia. What's the likelihood of bacteremia in a very well-appearing patient? It's very unlikely. True bacteremia is rare and when real may even resolve untreated. Remember, you are probably bacteremic transiently yesterday when you brushed your teeth. Okay, so we need test that can tell us quickly whether a child is at risk for bacteremia so we can distinguish well-appearing children who we should worry about versus those who we shouldn't and there are several tests out there. There seems to be early evidence that procalcitonin and CRP may in fact be better than the CBC in terms of screening for this but right now most people are still using a high white count. If the white count is above 15 or below 5, we worry a little bit about bacteremia. Coming soon to a theater near you is blood PCR.

    05:30 I suspect this may 1 day replace what we currently use as the goal standard test, which is culture. So right now we'll get these preliminary tests, a procalcitonin or a CRP or a CBC looking specifically at the white count and if those are normal we feel comfortable saying it's very unlikely this is a positive blood culture but if they're abnormal it might be. Hopefully with advent of blood PCR we don't need to wait for a definitive thing and we can get that blood PCR relatively quickly, typically takes about an hour and a half to get the test done. Okay, what about meningitis? You should send an LP in a baby if they have suspicion for meningitis. This is typically in children under 4 weeks of age and maybe in that 4 to 8-week range depending on whether you use the Philadelphia and Boston criteria as opposed to the Rochester criteria, we only do it if the white cell count is abnormal. So what labs should we send that cerebrospinal fluid for after we've obtained it? Well, the first is a cell count. In a patient with meningitis under a month of age, that cell count would be over 21. In a patient with meningitis who's between 1 and 2 months, it will be over 11. We should send that CSF for glucose and generally the glucose is about 2/3 of the blood glucose. So if it's less than that, it's more likely to be meningitis. If you want to think about it, this is not the pathophysiology but you can think about it as if the bacteria are eating glucose and making protein. So if there's bacterial meningitis, these patients will have a less than 2/3 of their serum glucose in their spinal fluid. Likewise, the protein will be high so if they have meningitis they should have a high protein above about 90. Gram stain is important and if the gram stain is positive, it's very likely this is bacterial meningitis but remember the false negative rate is high. So it's one of these things where if you see it you worry but if you don't see it you don't necessarily know. Culture is the goal standard and that's what we'll wait for but that takes couple of days and so these infants may be hospitalized for a period of time waiting for that culture to come back. However, if you send an enterovirus PCR in that test and it comes back positive which typically happens in the fall and winter months, you're done. It's a very accurate test and we will typically discontinue antibiotics and if the child is well send them home but keep in mind enterovirus meningitis can be very severe and sometimes these kids can get quite sick.

    About the Lecture

    The lecture The Febrile Baby: Urinary tract infection (UTI), Bacteremia & Meningitis by Brian Alverson, MD is from the course Pediatric Infectious Diseases. It contains the following chapters:

    • Pathology of UTI, Bacteremia and Meningitis
    • Diagnosis of Urinary Tract Infections
    • Diagnosis of Bacteremia
    • Diagnosis of Meningitis

    Included Quiz Questions

    1. Urinary tract infections
    2. Pneumonia
    3. Meningitis
    4. Bacteremia
    5. Cellulitis
    1. Osteomyelitis
    2. Meningitis
    3. Eye infections
    4. Rashes
    5. Runny nose
    1. CSF bacterial Culture
    2. Cell count of CSF
    3. CSF glucose
    4. Gram stain of CSF
    5. CSF protein
    1. Positive Enterovirus PCR of CSF
    2. CBC showing less than 5000 white blood cells/dl
    3. Cell count of CSF is normal or decreased
    4. Gram stain of CSF is negative
    5. CSF protein is high
    1. Nitrite test
    2. Elevated leukocyte count
    3. Presence of bacteria
    4. Positive leukocyte esterase test
    5. Overall interpretation of urinalysis

    Author of lecture The Febrile Baby: Urinary tract infection (UTI), Bacteremia & Meningitis

     Brian Alverson, MD

    Brian Alverson, MD

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    Great lecture!
    By Jalil Z. on 04. July 2020 for The Febrile Baby: Urinary tract infection (UTI), Bacteremia & Meningitis

    Great lecture! I learned tons. It shows that the instructor masters the topic and is able to give a clear and easy-to-understand picture. I now feel much more confident for these situations and more able to integrate the local guidelines now that I understand better the general concepts. Thanks!