A urinary tract infection (UTI) is an infection involving the kidneys, ureters, bladder, or urethra.  If left untreated, UTIs can lead to permanent kidney damage and sepsis.

Urinary tract infections don't always cause signs and symptoms, but when they do they may include:

  • A strong, persistent urge to urinate
  • A burning sensation when urinating
  • Passing frequent, small amounts of urine
  • Urine that appears cloudy
  • Urine that appears red, bright pink or cola-colored — a sign of blood in the urine
  • Strong-smelling urine
  • Pelvic pain, in women — especially in the center of the pelvis and around the area of the pubic bone

Each type of UTI may result in more-specific signs and symptoms, depending on which part of the urinary tract is infected.

Types of Urinary Tract Infection

Part of Urinary Tract Affected

Sign and Symptoms

Kidneys (acute pyelonephritis)

Upper back and side (flank) pain

High fever

Shaking and chills



Bladder (cystitis)

Pelvic pressure

Lower abdomen discomfort

Frequent, painful urination

Blood in urine

Urethra (urethritis)

Burning with urination



Each year, there are over 8 million cases of UTI in the United States. While people of any age or gender can develop a UTI, about four times as many women get them as men. Women have a shorter urethra, which makes it easier for bacteria to reach the bladder, and the opening of a woman’s urethra is closer to the anus, where bacteria live.

Escherichia coli (abbreviated as E. coli) is the bacterial culprit in 80% of all UTIs. While antibiotics work effectively against most E. coli, some strains, called extended-spectrum beta-lactamase (ESBL) E. coli, are resistant to many antibiotics.

The challenge in treating UTIs is that many of the oral antibiotics previously used have begun to develop antibiotic resistance.  From 2000 to 2010, the proportion of UTIs resistant to the fluoroquinolone antibiotic ciprofloxacin went from 3 percent to 17.1 percent. The alternative to oral antibiotics with high rates of antibiotic resistance is administration of intravenous antibiotics in the hospital or an infusion center.

In May 2016, a Philadelphia woman tested positive for a new superbug – a strain of E. coli resistant to one of the last-resort antibiotics called colistin was identified. Fortunately, her UTI was not invincible to all antibiotics. But as the bacteria that cause UTIs continue to mutate, scientists fear the time will come when one of the most common infections in the body becomes all but untreatable.