Urine Culture Results in Infants: Is There a UTI?

Urine culture

Hello, doctor.
I apologize for asking you again.
My baby boy is 5 months old and has mild hydronephrosis, with a left kidney measurement of 0.6 cm and a right kidney measurement of 0.3 cm.
He had a fever of 38.4 degrees Celsius and was taken to see a pediatrician, who performed a urinalysis and bacterial culture.
Interestingly, after a few hours without medication, the fever subsided, and he has not had a fever for the past 2-3 days.
The test results are as follows:
Test Name Result Reference Values
Bilirubin Negative
Color Straw [Yellow]
Glucose Negative
Ketone Negative
Protein Negative
Specific Gravity 1.010 [1.003][1.035]
Turbidity Clear
Urobilinogen Normal [Normal (2.0)]
WBC Negative
Esterease pH 7 [5][8]
Bacterial Culture Identification
Aerobic Mixed flora of clinical insignificance
I have a few questions for you, doctor:
1.
The routine urinalysis results are normal, but the bacterial culture shows mixed flora of clinical insignificance.
Does this mean my baby has a urinary tract infection? How could there be multiple bacteria present? Does he need antibiotics?
2.
We used a urine collection bag; what could have caused the bacterial culture to show mixed flora of clinical insignificance?
3.
My baby initially had a fever of 38.4 degrees Celsius, but it subsided after 3-4 hours without medication.
What could be the reason for this fever? What could have caused the fever to resolve on its own?

Mama, 30~39 year old female. Ask Date: 2022/10/09

Dr. Xiao Kaiwen reply Pediatrics

1.
The fever resolved without the use of antibiotics, and the urine test showed no evidence of a urinary tract infection, so antibiotics are not necessary.
2.
Urine ultimately passes through the mucous membranes and skin before reaching the urine bag, so it is still possible to culture non-pathogenic bacteria that are contaminants from the mucous membranes and skin.
3.
There could be many reasons, such as a hot and humid environment causing a temporary elevation in body temperature in infants whose thermoregulation is not fully developed, or common viral infections in infants that are not severe and are cleared by the immune system, leading to the resolution of the fever.

Reply Date: 2022/10/09

More Info

Understanding urine culture results in infants, particularly in the context of potential urinary tract infections (UTIs), can be quite complex. In your case, the urine culture showed "mixed flora of clinical insignificance," which is an important finding to interpret.

1. Urine Culture Results: The term "mixed flora of clinical insignificance" typically indicates that the bacteria found in the urine sample are not associated with a urinary tract infection. In infants, especially those under one year of age, the presence of bacteria in the urine can often be due to contamination during the collection process rather than an actual infection. Since the routine urine analysis showed normal results (negative for bilirubin, glucose, ketones, protein, and white blood cells), this further supports the idea that there is no significant infection present.
2. Need for Antibiotics: Given that the culture results are not indicative of a UTI and the infant's routine urine analysis is normal, there is generally no need for antibiotic treatment. Antibiotics are typically prescribed when there is clear evidence of a UTI, such as the presence of significant bacteria in the culture along with symptoms like fever, irritability, or poor feeding. In your case, since the infant's fever resolved on its own and there are no other concerning symptoms, the likelihood of a UTI is low.

3. Collection Method and Contamination: The use of a urine collection bag (often referred to as a "urine collection pouch") can sometimes lead to contamination, which is why mixed flora can appear in the culture results. This method is convenient but not always the most reliable for obtaining a sterile sample, especially in infants. If there is a suspicion of a UTI in the future, a clean-catch urine sample or a catheterized sample may provide more accurate results.

4. Fever Resolution: The fever your infant experienced (38.4 degrees Celsius) could have been due to a variety of reasons, including a viral infection, teething, or even a mild reaction to a recent vaccination. Infants can often have fevers that resolve spontaneously without the need for medication. The body's immune response can effectively manage many mild infections, which is likely what happened in your case.

5. Next Steps: If your infant continues to show signs of illness, such as persistent fever, irritability, or changes in feeding patterns, it would be prudent to follow up with your pediatrician. They may recommend further evaluation or monitoring. Additionally, if there are concerns about the kidney dilation (hydronephrosis) noted in your infant, it may be worthwhile to consult a pediatric nephrologist for further assessment.

In summary, based on the urine culture results and the normal routine analysis, it appears that your infant does not have a urinary tract infection. The fever may have been due to a benign viral illness or another non-infectious cause. Always consult your pediatrician for personalized medical advice and to address any ongoing concerns regarding your child's health.

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