As one of the most common bacterial infections in children, urinary tract infection (UTI) is a familiar foe for most general pediatricians. In a recently released article in Pediatrics, Mattoo et al provides a state-of-the-art review of current literature regarding UTIs1 which compliments the AAP 2016 clinical practice guidelines (10.1542/peds.2020-012138). Their article is a wonderful refresher on some forgotten facts about UTIs and is sprinkled with clinical pearls I’ve found to be very useful in practice.
One such pearl is a calculator developed at the University of Pittsburgh that assesses the likelihood of UTI in a febrile infant.2 Using a series of risk factors such as age, ethnicity, and temperature, the initial calculation leads to a recommendation for or against obtaining a urine sample. If urine is obtained, the results from urinalysis or urine dipstick are added to the calculator and the probability of a UTI is calculated. The calculator goes one step further and suggests or rejects the need for empiric treatment based on its overall estimate. Though I’ve only used this several times, I have found this calculator to be tremendously helpful since it aids in the reduction of unnecessary catheterization or antibiotic use.
The calculator’s initial emphasis on risk factors and clinical symptoms rather than laboratory data alone speaks to the limitations of the urine dipstick and culture in the diagnosis of UTI, which Mattoo et al discuss in detail. For instance, their review reminds us that while nitrite positive urine is highly specific for UTI, its sensitivity is rather low. Nitrites reflect the presence of gram-negative bacteria but can only be detected after several hours of urinary stasis, which makes it a less reliable indicator of UTI in an infant or young child who does not have voluntary bladder control.
Furthermore, while I’ve always thought the diagnosis of UTI required a colony count greater than 50,000 in culture, this definition has been hotly debated and some studies suggest that a much lower threshold should be used.3 It is indeed another reminder that while a urine dipstick or urine culture does have value, clinical acumen is our greatest tool for the diagnosis of UTI.
Lastly, here are a few high-yield points to take with you to your practice:
- A clean catch or catheterized urine sample should always be used for culture given a contamination rate as high as 80% with a bagged urine sample.
- A renal bladder ultrasound (RBUS) should be conducted with the first febrile UTI in children aged 2 to 24 months or after recurrent febrile UTIs in older children in order to rule out structural or anatomic anomalies.
- Voiding cystourethrogram should only be done in children with abnormalities on RBUS, prior history of renal scarring, family history of vesicoureteral reflux, an atypical pathogen, or a very complex clinical course.
- First line outpatient antibiotic therapy includes a 7 to 10 day course of a first or second generation cephalosporin, Bactrim or nitrofurantoin. Amoxicillin is not a good choice due to high resistance rates.
For a more in-depth review, be sure to check out the complete article in this month’s Pediatrics.
- Reaffirmation of AAP Clinical Practice Guideline: The Diagnosis and Management of the Initial Urinary Tract Infection in Febrile Infants and Young Children 2-24 Months of Age. (2016). Pediatrics, 138(6). doi:10.1542/peds.2016-3026
- Shaikh N, Hoberman A, Hum SW, et al. Development and Validation of a Calculator for Estimating the Probability 71 of Urinary Tract Infection in Young Febrile Children. JAMA Pediatr 2018; 172(6): 550-6.
- Roberts, K.B., & Wald, E. R. The Diagnosis of UTI: Colony Count Criteria Revisited. Pediatrics, 141 (2). doi: 10.1542/peds.2017-3239