Urinary tract infection (UTI) is defined as the presence and proliferation of germs in the urinary tract, which under normal conditions should be sterile. It affects any of the structures through which urine circulates from its formation in the kidneys to its expulsion through the urethra.
To explain it more simply, “urine is made in the kidneys and flows down the ureters to the bladder, where it is stored and when we pee, it comes out through the urethra”. Urine infection can affect any of these organs. It is called cystitis or lower urinary tract infection when it is located in the lower sections (bladder and urethra) and pyelonephritis or upper urinary tract infection when it affects the kidney.
Urinary tract infection can occur in two ways:
- Ascending route: Passage of germs from the perineal region to the urinary tract, more common in girls due to the proximity of the urethra to the rectum (contamination by feces).
- Hematogenous dissemination: Bacterial infection that causes contamination of the renal parenchyma.
UTI is the most frequent potentially serious bacterial infection in children under 36 months of age. The most common germ is E. coli (70-90% of infections).
What symptoms does it cause? How can it be detected?
In newborns and infants there are no typical clinical signs that lead us by themselves to a suspected urinary tract infection; the most common is to find a baby with fever or vomiting or with loss of appetite and/or poor weight gain, i.e. totally unspecific symptoms.
In older children the symptoms are more indicative, they may come to the office for pain when urinating, need to go to the bathroom many times (it is normal that they do little amount of urine), inability to hold urine and usually without fever. All this is usually seen in children with lower urinary tract infections (cystitis).
In upper urinary tract infections, the so-called pyelonephritis, in addition to these symptoms the child usually presents fever, general malaise and there may even be pain in the lower back.
Diagnosis
The suspected diagnosis must always be confirmed with a urinalysis. And this is where the problems begin.
There are different collection systems. In older children the collection system is very simple. The ideal is the direct collection in a sterile canister in the middle of the stream (the child starts to pee and when he has already peed a little he puts the canister under the stream without touching the penis) and preferably first thing in the morning, so that it is more concentrated.
The problem usually arises with small children and infants, here we can do it in different ways, by perineal bag, urethral catheterization or suprapubic puncture.
- The perineal bag
This is the method of collection best known to parents. It initially requires cleaning the perineum with soap and water and drying it with sterile gauze. Then the bag is firmly attached to the genital area (perineal area/urinary meatus) and very important if in 30 minutes he does not pee in the bag, it must be removed and the whole operation repeated.
The main drawback is the low reliability of the sample obtained with this method, so we find a very high number of false positives, i.e., although there is no infection, the number of leukocytes may appear altered and even the urine culture may be positive, although it is not. This is usually due to a defect in the collection due to defective sterilization or because the collection of the sample is delayed for 2-3 hours. As a general rule, urine culture should not be performed with samples collected by perineal bag. It is considered positive (infection) when there are more than 100,000 colonies/µL of a single type of bacteria.
- Urethral catheterization
It is the method of choice in children under 2 years of age. It is a quick and simple method, obtaining urine in almost 100% of cases. But it must be performed exclusively by health personnel. It consists of the introduction of a small catheter through the urinary meatus, which has been previously lubricated with a topical anesthetic, which significantly reduces the possible discomfort of catheterization. With this, an almost 100% sterile urine is obtained, so that the urine culture result will never be in doubt. It is considered positive when there are more than 25,000-50,000 colonies/µL.
- Suprapubic puncture
This is a hospital technique that requires the use of a needle to obtain urine directly from the urinary bladder. It is considered positive when there are more than 1,000 colonies/µL.
After collecting the urine sample under sterile conditions it must be sent to the laboratory to check the existence of a certain number of germs in the urine. This test is called urine culture and requires a few days to obtain the result (usually between 48-72h) and with it we will know on the one hand which bacteria cause the infection and on the other hand which antibiotic/s are suitable to destroy this germ.
There are rapid tests (test strips, urinary sediment analysis) that can indicate the presence of a urinary tract infection if they are altered (leukocytes, red blood cells, nitrites, etc.). Their reliability is not very high, but they serve as an initial orientation.
Blood tests are only used in children with suspected pyelonephritis.
When do we order imaging tests?
On some occasions, especially in the case of young children, boys or with upper urinary tract infection (pyelonephritis), pediatricians recommend imaging tests to check if there is any malformation that may favor urinary tract infections (ultrasound, cystography) or if the kidney may have been affected (scintigraphy – mTc-DMSA).
The main malformation that is usually investigated after a UTI is vesicoureteral reflux, which consists of the return to the kidneys of urine that was already in the bladder, due to a malfunction of a valve that prevents it under normal conditions, and which is a condition that can favor the possibility of new urinary tract infections.
What is its treatment?
The only treatment is antibiotic therapy, which can be given orally in lower urinary tract infections or intravenously (with hospital admission) in pyelonephritis with poor general condition or in young infants.
The most commonly used antibiotics are second and third generation cephalosporins, amoxicillin-clavulanic acid, fosfomycin, etc. All of them are very potent against E. coli bacteria. It is usual not to give the antibiotic until the result of the urine culture is available, but sometimes if the suspicion of infection is very clear, pediatricians give one of these antibiotics once the urine has been collected.
Prognosis
Usually urinary tract infections do not have harmful long-term consequences, especially if they are not frequent and/or only affect the lower urinary tract (cystitis). But if the infections are very repetitive or if they have not been treated, they can cause scars and lesions in the kidneys that can damage them and affect their function (renal failure, arterial hypertension, etc.).
For this reason, at the Valencian Institute of Pediatrics, by protocol, every child who has had a urinary tract infection, at the end of the antibiotic treatment, a new urine culture is performed to find out if the infection has disappeared. And even if this culture comes out well, 1 or 2 months later, it is repeated.