Urinary Tract Infections (UTI, Bladder Infection) in Children: Pathology & Diagnosis

00:00 In this lecture, we're going to review Urinary Tract Infections in Children. A urinary tract infection is an infection by bacteria of the bladder which is cystitis or the kidney which is pyelonephritis. The site of infection is harder to tell clinically in infants because they have a nonfocal exam. Older children will complain about pain while peeing, but it’ll be generally suprapubic in cystitis or they’ll have pain over their costovertebral angle to palpation when they have a pyelonephritis. About 7% of infants who have a fever have a urinary tract infection.

00:43 That’s generally speaking under, say, a year of age. The problem is is that our gold standard for testing for urinary tract infection, which is the urine culture, 1% of asymptomatic infants and adolescents will have bacteria in their urine, will have an abnormal urine culture, so the problem is if we see a febrile infant or adolescent and we’re suspecting urinary tract infection but we’re not sure, there is a 1% false positive rate. The most likely organism in a urinary tract infection is <i>E. col</i>i and that accounts for about 80% of urinary tract infections but there are are others that can pop up including <i>Klebsiella, Proteus, Citrobacter, Enterobacter,</i> <i>Enterococcus,</i> and <i>Enterococcus</i> is important because it’s resistant to many of the antibiotics that we might choose for a UTI, <i>Staphylococcus</i>, very rare and in particular it could be <i>Staph saprophyticus</i>, and <i>Pseudomonas</i>. So, what are the risk factors for infants and children getting urinary tract infection? The one that’s often missed is constipation. Constipation is really common in children and infants with urinary tract infections and managing constipation is critical to prevention of further urinary tract infections. Children with a history of vesicoureteral reflux or any other underlying nephropathy are at increased risk for urinary tract infections. This includes patients with horseshoe kidney, patients with ureteropelvic junction problems or posterior urethral valves. All of these things put children at increased risk for UTI. Patients with dysfunctional voiding such as the neurogenic bladder are at increased risk for UTI. So, for example, a patient with spina bifida who has to self cath is at very significant increased risk. Young children are at higher risk than older children. In particular, less than a month, it’s very common; under a year, it’s still very common but it gets less common as they age. Any girl after about 3 months of age is at increased risk over a boy for having a urinary tract infection. The penis provides some sort of protective capacity. In children under 3 months of age, because oftentimes urinary tract infections are pyelonephritis, which is spread through bacterial spread of the bacteria, in fact males are slightly more likely to have UTI very early in infancy than females. So this really doesn’t cross over until about 3 months of age. In adolescents, especially adolescent girls, sexual activity increases risk of urinary tract infection. So, here are the 2 methods by which children are most likely to get a urinary tract infection. There is bacteremia that then lands in the kidney and causes a pyelonephritis and that tract infection descends downward, that's more common in infants and then there is ascending urinary tract infections. Most people at some point are bacteruiric, they get a little bit of bacteria in their bladder. Those bacteria are continuously flushed out through the process of urination. Occasionally, those bacteria can ascend upwards through the urethra and the ureter and up into the kidney, so an ascending infection is also possible. In general, in infants under 2 years of age, they will present with relatively nonspecific findings: fever, irritability, and poor feeding, sometimes vomiting. Over 2 years of age, you’re more likely to get a good story for it. They’ll have the fever but they may have CVA tenderness or bladder tenderness. They may complain of dysuria and they often have urgency or incontinence. So, if we suspect a urinary tract infection, it’s important to collect some urine. There are several different techniques we can use. In children who can pee on command, we can do a clean catch where we have them clean themselves off, pee a little bit on the toilet and put the rest in the cup. That’s very effective. For younger children, we may choose to do a bag urine. The problem with bag urine is there is a higher false positive rate. So, patients may have some contamination in that bag of a little fecal material, which will look like a urinary tract infection. However, if the bag urine is negative, you can assume that the child does not have a urinary tract infection. Catheterized urine is probably the way to go in these younger children in that when you catheterize them, you can get a cleaner specimen and you're less likely to have a false positive. In catheterized urine, we then go and insert a catheter into the urethra of the patient and up into the bladder and collect the urine. Of course, it’s sterilized first. Catheterized urine is appropriate to send for culture although bag urine generally not.

05:51 Another more invasive way one could collect urine is through a suprapubic tap or aspiration.

05:57 This is when a needle is introduced directly through the abdominal wall generally slightly angling downward just over the pubic symphysis. This is generally a fairly effective way and in experienced hands, you usually get a result. There’s not much risk for perforation of viscous because you’re going directly into the bladder. However, this is a very painful experience and generally we prefer to do catheterized sampling. The urinalysis is a very effective test for a urinary tract infection. It is in fact 98% sensitive. However, it’s only 65% specific. That means it has about a 35% fall positive rate. A urinalysis has a likelihood of showing you when you have a urinary tract infection a positive result but when you don’t, it has a reasonable shot of still showing you a positive result. The elements of the urinalysis that indicate whether a patient have a urinary tract infection include white count, red count, leuk esterase, and nitrites. Remember that if nitrites is positive that means you almost definitely have a UTI, but many UTIs do not have positive nitrites. So, let’s say that we have a urinalysis and we suspect the patient has a UTI, what is the gold standard? Well, the gold standard is culture but remember the culture is not that golden. By that I mean that many patients, 1%, will have a false positive urinary tract infection culture because they have asymptomatic bacteriuria and there’s something else going on. For a suprapubic tap, we recommend that any bacteria counts as a positive urine culture.

07:44 For a catheterized specimen, we generally use more than 10,000 although the new AEP Guidelines recommends 50,000. There’s not a lot of evidence for that 10,000-50,000 range in terms of whether these are likely to be positives or negatives and it is difficult to determine because of asymptomatic bacteriuria and not having a really clear gold standard. That said, you can either use 10,000 or 50,000 as your cut off for a catheter specimen. Generally, for a clean catch, we use 100,000. These are rough estimates. Remember, there is no real gold standard here and many times we’ll just use our clinical suspicion in combination with these data. What’s key is you should not obtain a bag urine to check for a culture because of the false positive rate and remember there’s no blood test that is diagnostic of a UTI. There is no role for getting a CBC when you’re trying to rule out a urinary tract infection.