Otto Busato, M.D. Internal Medicine and Nephrology Specialist by the Brazilian Medical Association. MA/PH.D., Rio Grande do Sul State University (UFRGS). Associate Professor at the Rio Grande do Sul State University School of Medicine (UFRGS).

Urinary tract infection (UTI) is one of the main causes for visiting a doctor, and is second only to respiratory infections.

Thus, it’s important to define and characterize urinary infection, as well as explain the expressions mostly used by doctors.

In the second article, we’ll address cystitis (lower urinary tract infection), and in the third, pyelonephritis (upper urinary tract infection).

In the fourth article, we’ll address child urinary infections, and in the fifth, urinary infections in pregnant women.

Thus, we advise to read the articles sequentially, as they approach urinary tract infections from different perspectives.

What is it?

UTI is the presence of microorganisms somewhere in the urinary tract. When it appears in the kidneys, it’s called pyelonephritis; in the urinary bladder, cystitis; in the prostate, prostatitis; and in the urethra, urethritis.

Most UTIs are caused by bacteria, but they can also be generated by virus, fungi and other microorganisms. Most urinary infections occur due to some bacteria’s invasion from the urinary tract’s intestinal bacterial flora. Escherichia coli makes up 80-95% of all urinary tract-infecting invaders.

At times, the patient has symptoms similar to those of UTI, such as pain, burning, urinary urgency, and increased urination frequency, yet culture tests don’t reveal bacteria in the urine.

These cases may be confused with UTI and are called acute urethral syndrome, which may have non-infectious causes of inflammatory origin, such as chemical, toxic, hormonal and radiation causes.

How does it occur?

Microorganisms gain access to the urinary tract in an upward direction, that is, via urethra, and may settle down in the urethra proper and prostate, advancing into the bladder, and, more hardly, into the kidneys.

Bacteria can barely penetrate the urinary tract via bloodstream. This takes place only when there’s general infection (septicemia), or in individuals without immune defenses as AIDS and transplant patients. UTI intensity depends upon patient defense, the microorganisms’ virulence, and their ability to adhere to the urinary tract wall.

As urine is sterile, there are factors that facilitate urinary tract contamination, such as:

Urinary obstruction: augmented prostate, urethral stenosis, congenital defects, etc;

Foreign bodies: probes, calculi (kidney stones), introduction of objects into the urethra (kids);

Neurologic diseases: spinal column trauma, diabetes-associated neurogenic bladder;

Genitourinary and digestive tract fistulas, colostomized and constipated individuals;

Sexually transmitted diseases and gynecologic infections.

Preventive and therapeutic information on these facilitating factors can be seen in the articles on cystitis, pyelonephritis, and UTI in pregnant women and children.

What does one experience?

Urination is voluntary and painless. The presence of:

difficulty and/or urgency for urinating
very frequent urination in small quantity
cloudy, strong smelling urine
urine with mucous filaments

make up a set of data that allow the physician to suspect a patient is suffering from UTI. Often, bladder pain and bloody drops in the end of urination add to these symptoms and signs. When the kidney is involved, the patient has chills, fever, lumbar pain in addition to the previous symptoms; also, abdominal pain, nausea and vomiting sometimes may occur.

How is it diagnosed?

The presence of UTI signs and symptoms compels the doctor to ask for a standard urine test and urine culture. For this, it’s very important that urine sample collection be performed without contamination. Contamination usually is caused by microorganisms from the urethra, perianal region, and sometimes from cough or the hands handling the sterile vials.

There are four collection methods: midstream clean-catch, bag-collection, catheterization, and suprapubic bladder aspiration. Each of these has its indications, advantages and drawbacks. The physician must decide which one is best for his/her patient.

Most sample collections are performed by collecting the midstream from the first urination in the morning, following careful periurethral cleaning. The midstream is the one collected after the first portion of urine is discarded, which could be contaminated by urethral microorganisms.

The standard urine test, in case of UTI, displays bacteria and a great amount of leukocytes (white blood cells) prevailing over erythrocytes (red blood cells) in the urinary sediment.

The urine culture test for UTI demonstrates a bacterial growth higher than 100,000 germs/mL of urine. This amount of bacteria allows UTI diagnosis in more than 95% of the cases, as long as no contamination has occurred. Some times, in certain situations a lower number of bacteria can also be indicative of UTI.

It’s noteworthy to observe that urine is sterile and should not carry bacteria.

Keep on reading about UTI in the articles on cystitis and pyelonephritis.


FISTULA: a communication between two cavities, as may occur between the bladder and the vagina (vesicovaginal fistula).

COLOSTOMIZED PATIENT: patient that needs to defecate into special pouches as a result from an abnormal anus.