Urinary tract infections affect millions of people each year. And in the majority of cases, a quick dose of antibiotics will take care of the problem.

But this wasn’t the case for 20-year-old Brazilian beauty queen Mariana Bridi da Costa, the Miss World finalist who recently had her hands and feet amputated after contracting a severe urinary infection.

Click here for photos of Bridi da Costa.

“I have seen people get septic from a urinary tract infection that goes untreated, but never amputation,” Dr. Debra Fromer, Chief of the Center for Bladder Prostate and Pelvic Floor Health at Hackensack University Medical Center in New Jersey, told FOXNews.com

“This is incredibly rare.”

Bridi da Costa fell ill on Dec. 30 and went to a hospital in the Brazilian city of Serra. She was misdiagnosed with kidney stones and sent home.

How doctors came to that diagnosis is not clear. Fromer said if someone comes in with severe pain on her side, especially over the kidney, several procedures are performed.

“If a kidney stone is suspected, usually an ultrasound or a CT scan is performed to rule out kidney stones,” Fromer said.

Bridi da Costa's infection worsened and she returned to the hospital, but it was too late. Septicemia — the presence of bacteria in the blood — had set in her limbs, cutting off circulation.

"They gave her some medicine and sent her home,” her boyfriend Thiago Simoes said. "We took her back to hospital and they said she had a very serious infection. She got more and more sick, and had no blood circulation to her limbs. First she lost her feet, and then on Tuesday she lost both her hands.”

Urinary tract infections, or UTIs, occur in males and females of all ages, but they are much more common in women.

“The female urethra is very short,” Fromer said. “So, usually in young women … an infection may occur due to intercourse. This happens because the normal bacteria that lives in the urogenital region can easily be transferred from the back side to front side. Then what happens is you get a bladder infection.”

Symptoms include:

— A strong, persistent urge to urinate;

— A burning sensation when urinating;

— Passing frequent, small amounts of urine;

— Blood in the urine or cloudy, strong-smelling urine.

A UTI may occur anywhere along the urinary tract, which includes the kidneys, bladder, ureters — the tubes that take urine from each kidney to the bladder — and the urethra — the tube that empties urine from the bladder to the outside, according to the National Institutes of Health.

Mild UTIs may disappear on their own, but antibiotics are usually recommended to prevent the infection from spreading to the kidneys.

The infections usually disappear within 24 to 48 hours of treatment, though some take up to a week to clear up. Complications, like the life-threatening blood infection or sepsis that affected Bridi da Costa, are rare.

Other rare complications include kidney damage or scarring and kidney infection, according to the NIH’s Medline Plus Web site.

“My advice is to call a doctor, get some antibiotics and don’t let it progress,” Fromer said.