Babies with urinary tract infections rarely show the obvious signs older kids do, like crying during urination or asking to go to the bathroom constantly. Instead, a UTI in an infant often looks like a general illness: unexplained fever, fussiness, poor feeding, or strong-smelling urine. Knowing what to watch for can help you catch it early, before the infection has a chance to spread.
Common Signs in Babies Under 2
The symptoms of a UTI in a baby depend partly on age. Newborns may develop jaundice (yellowing of the skin or eyes), vomiting, failure to gain weight, or signs of a serious bloodstream infection like fever with lethargy. These overlap with many other newborn conditions, which is why UTIs in the first weeks of life are often caught through routine testing rather than a parent spotting a telltale sign.
In older infants and toddlers, the picture becomes a bit clearer. The most common signs include:
- Fever with no obvious cause. This is the single biggest red flag. If your baby has a temperature of 100.4°F (38°C) or higher and you can’t point to a cold, ear infection, or teething as the reason, a UTI is one of the first things your pediatrician will consider.
- Strong or foul-smelling urine. A noticeably unpleasant smell when you change the diaper is one of the few UTI-specific clues in babies.
- Irritability or fussiness that seems out of proportion or doesn’t respond to the usual comfort measures.
- Vomiting or refusing to eat. Babies can’t tell you their belly hurts, so gastrointestinal symptoms sometimes stand in for the abdominal or flank pain an older child would describe.
- Blood in the urine. You might notice a pinkish tinge on the diaper.
None of these signs on their own confirms a UTI, and many babies with UTIs have fever as their only symptom. That’s why testing matters so much in this age group.
When Fever Alone Triggers Testing
The American Academy of Pediatrics has specific guidance for babies aged 2 to 24 months with unexplained fever. Certain risk factors make a UTI more likely and prompt doctors to test sooner: being female, being an uncircumcised male, having a fever of 102.2°F (39°C) or higher, having no other clear source for the fever, and having a fever that lasts more than two days. In girls, being under 12 months old adds additional risk. In boys, fever lasting 24 hours or longer raises concern.
If your baby fits several of these categories, your pediatrician will likely want a urine sample even if no other symptoms are present. A fever of unknown origin in a young infant is one of the most common reasons UTIs get diagnosed in this age group.
How Doctors Test for a UTI
Getting a reliable urine sample from a baby who wears diapers is trickier than it sounds, and the method matters a lot.
The adhesive bag that sticks to the skin around the diaper area is the easiest option, but it’s also the least reliable. Studies show false-positive culture results from bag specimens range from 85% to 99%, meaning bacteria from the skin frequently contaminate the sample. A bag specimen can be useful for ruling out a UTI (if the result is negative, the baby probably doesn’t have one), but a positive result from a bag sample alone isn’t enough to confirm the diagnosis.
For children under two, the recommended approach is a catheterized sample, where a thin, sterile tube is briefly inserted into the urethra. It’s quick and uncomfortable but not harmful, and it gives a much more accurate result. Your doctor may also do a quick dipstick test on the urine while you wait. Automated dipstick testing in infants older than 28 days catches about 87.5% of UTIs, though accuracy drops in newborns under a month old (catching only about 53% of infections) and tends to produce more false positives in girls due to sample contamination.
The definitive test is a urine culture, where the sample is sent to a lab to see if bacteria grow. Results typically take one to two days. Your doctor may start antibiotics before the culture comes back if the dipstick or your baby’s symptoms are concerning enough.
Signs the Infection May Be Serious
Most infant UTIs are treatable and resolve without complications, but a small number can spread to the kidneys or bloodstream. In babies, this progression can happen faster than in older children because their immune systems are still developing.
Take your baby to the emergency room if you notice a combination of high fever with chills, rapid breathing, a weak or unusually fast pulse, extreme lethargy or difficulty waking, or if your baby stops producing wet diapers (a sign they may not be urinating). These can indicate the infection has moved beyond the bladder and needs urgent treatment.
What Treatment Looks Like
A confirmed UTI in a baby aged 2 to 24 months is treated with antibiotics for 7 to 14 days, depending on severity. Your baby will likely start to seem better within 48 to 72 hours, but finishing the full course is important to clear the infection completely and reduce the chance of it coming back.
Very young infants, especially those under two months, or babies who are vomiting too much to keep oral medication down, may need to receive their initial treatment in the hospital through an IV before transitioning to oral antibiotics at home. Your pediatrician may also recommend follow-up imaging of the urinary tract after the infection clears, particularly if it’s your baby’s first UTI, to check for any structural differences in the kidneys or bladder that could make infections more likely to recur.
Reducing the Risk of Future Infections
You can’t prevent every UTI, but a few habits lower the odds of bacteria reaching the urinary tract in the first place. Change diapers promptly after they’re soiled, and apply a moisture barrier like petroleum jelly or zinc oxide cream to protect the skin and reduce bacterial growth in the diaper area. For girls, always wipe front to back.
Once your child is out of diapers, dress them in cotton underwear and pajama bottoms rather than synthetic fabrics, which trap moisture. Showers or plain water baths are better than bubble baths or bath oils, which can irritate the urethra. Letting your baby go diaper-free for short stretches when practical also helps by airing out the skin and reducing the warm, moist environment bacteria thrive in.